Internet Engineering Task Force (IETF) R. Moskowitz, Ed.
Request for Comments: 7401 HTT Consulting
Obsoletes: 5201 T. Heer
Category: Standards Track Hirschmann Automation and Control
ISSN: 2070-1721 P. Jokela
Ericsson Research NomadicLab
T. Henderson
University of Washington
April 2015
Host Identity Protocol Version 2 (HIPv2)
Abstract
This document specifies the details of the Host Identity Protocol
(HIP). HIP allows consenting hosts to securely establish and
maintain shared IP-layer state, allowing separation of the identifier
and locator roles of IP addresses, thereby enabling continuity of
communications across IP address changes. HIP is based on a Diffie-
Hellman key exchange, using public key identifiers from a new Host
Identity namespace for mutual peer authentication. The protocol is
designed to be resistant to denial-of-service (DoS) and man-in-the-
middle (MitM) attacks. When used together with another suitable
security protocol, such as the Encapsulating Security Payload (ESP),
it provides integrity protection and optional encryption for upper-
layer protocols, such as TCP and UDP.
This document obsoletes RFC 5201 and addresses the concerns raised by
the IESG, particularly that of crypto agility. It also incorporates
lessons learned from the implementations of RFC 5201.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc7401.
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Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction ....................................................5
1.1. A New Namespace and Identifiers ............................6
1.2. The HIP Base Exchange (BEX) ................................6
1.3. Memo Structure .............................................7
2. Terms and Definitions ...........................................7
2.1. Requirements Terminology ...................................7
2.2. Notation ...................................................8
2.3. Definitions ................................................8
3. Host Identity (HI) and Its Structure ............................9
3.1. Host Identity Tag (HIT) ...................................10
3.2. Generating a HIT from an HI ...............................11
4. Protocol Overview ..............................................12
4.1. Creating a HIP Association ................................12
4.1.1. HIP Puzzle Mechanism ...............................14
4.1.2. Puzzle Exchange ....................................15
4.1.3. Authenticated Diffie-Hellman Protocol with
DH Group Negotiation ...............................17
4.1.4. HIP Replay Protection ..............................18
4.1.5. Refusing a HIP Base Exchange .......................19
4.1.6. Aborting a HIP Base Exchange .......................20
4.1.7. HIP Downgrade Protection ...........................20
4.1.8. HIP Opportunistic Mode .............................21
4.2. Updating a HIP Association ................................24
4.3. Error Processing ..........................................24
4.4. HIP State Machine .........................................25
4.4.1. State Machine Terminology ..........................26
4.4.2. HIP States .........................................27
4.4.3. HIP State Processes ................................28
4.4.4. Simplified HIP State Diagram .......................35
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4.5. User Data Considerations ..................................37
4.5.1. TCP and UDP Pseudo Header Computation for
User Data ..........................................37
4.5.2. Sending Data on HIP Packets ........................37
4.5.3. Transport Formats ..................................37
4.5.4. Reboot, Timeout, and Restart of HIP ................37
4.6. Certificate Distribution ..................................38
5. Packet Formats .................................................38
5.1. Payload Format ............................................38
5.1.1. Checksum ...........................................40
5.1.2. HIP Controls .......................................40
5.1.3. HIP Fragmentation Support ..........................40
5.2. HIP Parameters ............................................41
5.2.1. TLV Format .........................................44
5.2.2. Defining New Parameters ............................46
5.2.3. R1_COUNTER .........................................47
5.2.4. PUZZLE .............................................48
5.2.5. SOLUTION ...........................................49
5.2.6. DH_GROUP_LIST ......................................50
5.2.7. DIFFIE_HELLMAN .....................................51
5.2.8. HIP_CIPHER .........................................52
5.2.9. HOST_ID ............................................54
5.2.10. HIT_SUITE_LIST ....................................56
5.2.11. TRANSPORT_FORMAT_LIST .............................58
5.2.12. HIP_MAC ...........................................59
5.2.13. HIP_MAC_2 .........................................59
5.2.14. HIP_SIGNATURE .....................................60
5.2.15. HIP_SIGNATURE_2 ...................................61
5.2.16. SEQ ...............................................61
5.2.17. ACK ...............................................62
5.2.18. ENCRYPTED .........................................62
5.2.19. NOTIFICATION ......................................64
5.2.20. ECHO_REQUEST_SIGNED ...............................67
5.2.21. ECHO_REQUEST_UNSIGNED .............................68
5.2.22. ECHO_RESPONSE_SIGNED ..............................69
5.2.23. ECHO_RESPONSE_UNSIGNED ............................69
5.3. HIP Packets ...............................................70
5.3.1. I1 - the HIP Initiator Packet ......................71
5.3.2. R1 - the HIP Responder Packet ......................72
5.3.3. I2 - the Second HIP Initiator Packet ...............75
5.3.4. R2 - the Second HIP Responder Packet ...............76
5.3.5. UPDATE - the HIP Update Packet .....................77
5.3.6. NOTIFY - the HIP Notify Packet .....................78
5.3.7. CLOSE - the HIP Association Closing Packet .........78
5.3.8. CLOSE_ACK - the HIP Closing Acknowledgment Packet ..79
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5.4. ICMP Messages .............................................79
5.4.1. Invalid Version ....................................79
5.4.2. Other Problems with the HIP Header and
Packet Structure ...................................80
5.4.3. Invalid Puzzle Solution ............................80
5.4.4. Non-existing HIP Association .......................80
6. Packet Processing ..............................................80
6.1. Processing Outgoing Application Data ......................81
6.2. Processing Incoming Application Data ......................82
6.3. Solving the Puzzle ........................................83
6.4. HIP_MAC and SIGNATURE Calculation and Verification ........84
6.4.1. HMAC Calculation ...................................84
6.4.2. Signature Calculation ..............................87
6.5. HIP KEYMAT Generation .....................................89
6.6. Initiation of a HIP Base Exchange .........................90
6.6.1. Sending Multiple I1 Packets in Parallel ............91
6.6.2. Processing Incoming ICMP Protocol
Unreachable Messages ...............................92
6.7. Processing of Incoming I1 Packets .........................92
6.7.1. R1 Management ......................................94
6.7.2. Handling of Malformed Messages .....................94
6.8. Processing of Incoming R1 Packets .........................94
6.8.1. Handling of Malformed Messages .....................97
6.9. Processing of Incoming I2 Packets .........................97
6.9.1. Handling of Malformed Messages ....................100
6.10. Processing of Incoming R2 Packets .......................101
6.11. Sending UPDATE Packets ..................................101
6.12. Receiving UPDATE Packets ................................102
6.12.1. Handling a SEQ Parameter in a Received
UPDATE Message ...................................103
6.12.2. Handling an ACK Parameter in a Received
UPDATE Packet ....................................104
6.13. Processing of NOTIFY Packets ............................104
6.14. Processing of CLOSE Packets .............................105
6.15. Processing of CLOSE_ACK Packets .........................105
6.16. Handling State Loss .....................................105
7. HIP Policies ..................................................106
8. Security Considerations .......................................106
9. IANA Considerations ...........................................109
10. Differences from RFC 5201 ....................................113
11. References ...................................................117
11.1. Normative References ....................................117
11.2. Informative References ..................................119
Appendix A. Using Responder Puzzles ..............................122
Appendix B. Generating a Public Key Encoding from an HI ..........123
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Appendix C. Example Checksums for HIP Packets ....................123
C.1. IPv6 HIP Example (I1 Packet) ..............................124
C.2. IPv4 HIP Packet (I1 Packet) ...............................124
C.3. TCP Segment ...............................................125
Appendix D. ECDH and ECDSA 160-Bit Groups ........................125
Appendix E. HIT Suites and HIT Generation ........................125
Acknowledgments ..................................................127
Authors' Addresses ...............................................128
1. Introduction
This document specifies the details of the Host Identity Protocol
(HIP). A high-level description of the protocol and the underlying
architectural thinking is available in the separate HIP architecture
description [HIP-ARCH]. Briefly, the HIP architecture proposes an
alternative to the dual use of IP addresses as "locators" (routing
labels) and "identifiers" (endpoint, or host, identifiers). In HIP,
public cryptographic keys, of a public/private key pair, are used as
host identifiers, to which higher-layer protocols are bound instead
of an IP address. By using public keys (and their representations)
as host identifiers, dynamic changes to IP address sets can be
directly authenticated between hosts, and if desired, strong
authentication between hosts at the TCP/IP stack level can be
obtained.
This memo specifies the base HIP protocol ("base exchange") used
between hosts to establish an IP-layer communications context, called
a HIP association, prior to communications. It also defines a packet
format and procedures for updating and terminating an active HIP
association. Other elements of the HIP architecture are specified in
other documents, such as:
o "Using the Encapsulating Security Payload (ESP) Transport Format
with the Host Identity Protocol (HIP)" [RFC7402]: how to use the
Encapsulating Security Payload (ESP) for integrity protection and
optional encryption
o "Host Mobility with the Host Identity Protocol" [HIP-HOST-MOB]:
how to support host mobility in HIP
o "Host Identity Protocol (HIP) Domain Name System (DNS) Extension"
[HIP-DNS-EXT]: how to extend DNS to contain Host Identity
information
o "Host Identity Protocol (HIP) Rendezvous Extension"
[HIP-REND-EXT]: using a rendezvous mechanism to contact mobile HIP
hosts
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Since the HIP base exchange was first developed, there have been a
few advances in cryptography and attacks against cryptographic
systems. As a result, all cryptographic protocols need to be agile.
That is, the ability to switch from one cryptographic primitive to
another should be a part of such protocols. It is important to
support a reasonable set of mainstream algorithms to cater to
different use cases and allow moving away from algorithms that are
later discovered to be vulnerable. This update to the base exchange
includes this needed cryptographic agility while addressing the
downgrade attacks that such flexibility introduces. In addition,
Elliptic Curve support via Elliptic Curve DSA (ECDSA) and Elliptic
Curve Diffie-Hellman (ECDH) has been added.
1.1. A New Namespace and Identifiers
The Host Identity Protocol introduces a new namespace, the Host
Identity namespace. Some ramifications of this new namespace are
explained in the HIP architecture description [HIP-ARCH].
There are two main representations of the Host Identity, the full
Host Identity (HI) and the Host Identity Tag (HIT). The HI is a
public key and directly represents the Identity of a host. Since
there are different public key algorithms that can be used with
different key lengths, the HI, as such, is unsuitable for use as a
packet identifier, or as an index into the various state-related
implementation structures needed to support HIP. Consequently, a
hash of the HI, the Host Identity Tag (HIT), is used as the
operational representation. The HIT is 128 bits long and is used
in the HIP headers and to index the corresponding state in the
end hosts. The HIT has an important security property in that it
is self-certifying (see Section 3).
1.2. The HIP Base Exchange (BEX)
The HIP base exchange is a two-party cryptographic protocol used to
establish communications context between hosts. The base exchange is
a SIGMA-compliant [KRA03] four-packet exchange. The first party is
called the Initiator and the second party the Responder. The
protocol exchanges Diffie-Hellman [DIF76] keys in the 2nd and 3rd
packets, and authenticates the parties in the 3rd and 4th packets.
The four-packet design helps to make HIP resistant to DoS attacks.
It allows the Responder to stay stateless until the IP address and
the cryptographic puzzle are verified. The Responder starts the
puzzle exchange in the 2nd packet, with the Initiator completing it
in the 3rd packet before the Responder stores any state from the
exchange.
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The exchange can use the Diffie-Hellman output to encrypt the Host
Identity of the Initiator in the 3rd packet (although Aura, et al.
[AUR05] note that such operation may interfere with packet-inspecting
middleboxes), or the Host Identity may instead be sent unencrypted.
The Responder's Host Identity is not protected. It should be noted,
however, that both the Initiator's and the Responder's HITs are
transported as such (in cleartext) in the packets, allowing an
eavesdropper with a priori knowledge about the parties to identify
them by their HITs. Hence, encrypting the HI of any party does not
provide privacy against such an attacker.
Data packets start to flow after the 4th packet. The 3rd and 4th HIP
packets may carry a data payload in the future. However, the details
of this may be defined later.
An existing HIP association can be updated using the update mechanism
defined in this document, and when the association is no longer
needed, it can be closed using the defined closing mechanism.
Finally, HIP is designed as an end-to-end authentication and key
establishment protocol, to be used with Encapsulating Security
Payload (ESP) [RFC7402] and other end-to-end security protocols. The
base protocol does not cover all the fine-grained policy control
found in Internet Key Exchange (IKE) [RFC7296] that allows IKE to
support complex gateway policies. Thus, HIP is not a complete
replacement for IKE.
1.3. Memo Structure
The rest of this memo is structured as follows. Section 2 defines
the central keywords, notation, and terms used throughout the rest of
the document. Section 3 defines the structure of the Host Identity
and its various representations. Section 4 gives an overview of the
HIP base exchange protocol. Sections 5 and 6 define the detailed
packet formats and rules for packet processing. Finally, Sections 7,
8, and 9 discuss policy, security, and IANA considerations,
respectively.
2. Terms and Definitions
2.1. Requirements Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
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2.2. Notation
[x] indicates that x is optional.
{x} indicates that x is encrypted.
X(y) indicates that y is a parameter of X.
<x>i indicates that x exists i times.
--> signifies "Initiator to Responder" communication (requests).
<-- signifies "Responder to Initiator" communication (replies).
| signifies concatenation of information (e.g., X | Y is the
concatenation of X with Y).
Ltrunc (H(x), #K)
denotes the lowest-order #K bits of the result of the
hash function H on the input x.
2.3. Definitions
HIP base exchange (BEX): The handshake for establishing a new HIP
association.
Host Identity (HI): The public key of the signature algorithm that
represents the identity of the host. In HIP, a host proves its
identity by creating a signature with the private key belonging to
its HI (cf. Section 3).
Host Identity Tag (HIT): A shorthand for the HI in IPv6 format. It
is generated by hashing the HI (cf. Section 3.1).
HIT Suite: A HIT Suite groups all cryptographic algorithms that are
required to generate and use an HI and its HIT. In particular,
these algorithms are 1) the public key signature algorithm, 2) the
hash function, and 3) the truncation (cf. Appendix E).
HIP association: The shared state between two peers after completion
of the BEX.
HIP packet: A control packet carrying a HIP packet header relating
to the establishment, maintenance, or termination of the HIP
association.
Initiator: The host that initiates the BEX. This role is typically
forgotten once the BEX is completed.
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Responder: The host that responds to the Initiator in the BEX. This
role is typically forgotten once the BEX is completed.
Responder's HIT hash algorithm (RHASH): The hash algorithm used for
various hash calculations in this document. The algorithm is the
same as is used to generate the Responder's HIT. The RHASH is the
hash function defined by the HIT Suite of the Responder's HIT
(cf. Section 5.2.10).
Length of the Responder's HIT hash algorithm (RHASH_len): The
natural output length of RHASH in bits.
Signed data: Data that is signed is protected by a digital signature
that was created by the sender of the data by using the private
key of its HI.
KDF: The Key Derivation Function (KDF) is used for deriving the
symmetric keys from the Diffie-Hellman key exchange.
KEYMAT: The keying material derived from the Diffie-Hellman key
exchange by using the KDF. Symmetric keys for encryption and
integrity protection of HIP packets and encrypted user data
packets are drawn from this keying material.
3. Host Identity (HI) and Its Structure
In this section, the properties of the Host Identity and Host
Identity Tag are discussed, and the exact format for them is defined.
In HIP, the public key of an asymmetric key pair is used as the Host
Identity (HI). Correspondingly, the host itself is defined as the
entity that holds the private key of the key pair. See the HIP
architecture specification [HIP-ARCH] for more details on the
difference between an identity and the corresponding identifier.
HIP implementations MUST support the Rivest Shamir Adleman [RSA]
public key algorithm and the Elliptic Curve Digital Signature
Algorithm (ECDSA) for generating the HI as defined in Section 5.2.9.
Additional algorithms MAY be supported.
A hashed encoding of the HI, the Host Identity Tag (HIT), is used in
protocols to represent the Host Identity. The HIT is 128 bits long
and has the following three key properties: i) it is the same length
as an IPv6 address and can be used in fixed address-sized fields in
APIs and protocols; ii) it is self-certifying (i.e., given a HIT, it
is computationally hard to find a Host Identity key that matches the
HIT); and iii) the probability of a HIT collision between two hosts
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is very low; hence, it is infeasible for an attacker to find a
collision with a HIT that is in use. For details on the security
properties of the HIT, see [HIP-ARCH].
The structure of the HIT is defined in [RFC7343]. The HIT is an
Overlay Routable Cryptographic Hash Identifier (ORCHID) and consists
of three parts: first, an IANA-assigned prefix to distinguish it from
other IPv6 addresses; second, a four-bit encoding of the algorithms
that were used for generating the HI and the hashed representation of
HI; third, a 96-bit hashed representation of the Host Identity. The
encoding of the ORCHID generation algorithm and the exact algorithm
for generating the hashed representation are specified in Appendix E
and [RFC7343].
Carrying HIs and HITs in the header of user data packets would
increase the overhead of packets. Thus, it is not expected that they
are carried in every packet, but other methods are used to map the
data packets to the corresponding HIs. In some cases, this makes it
possible to use HIP without any additional headers in the user data
packets. For example, if ESP is used to protect data traffic, the
Security Parameter Index (SPI) carried in the ESP header can be used
to map the encrypted data packet to the correct HIP association.
3.1. Host Identity Tag (HIT)
The Host Identity Tag is a 128-bit value -- a hashed encoding of the
Host Identifier. There are two advantages of using a hashed encoding
over the actual variable-sized Host Identity public key in protocols.
First, the fixed length of the HIT keeps packet sizes manageable and
eases protocol coding. Second, it presents a consistent format for
the protocol, independent of the underlying identity technology
in use.
RFC 7343 [RFC7343] specifies 128-bit hash-based identifiers, called
ORCHIDs. Their prefix, allocated from the IPv6 address block, is
defined in [RFC7343]. The Host Identity Tag is one type of ORCHID.
This document extends the original, experimental HIP specification
[RFC5201] with measures to support crypto agility. One of these
measures allows different hash functions for creating a HIT. HIT
Suites group the sets of algorithms that are required to generate and
use a particular HIT. The Suites are encoded in HIT Suite IDs.
These HIT Suite IDs are transmitted in the ORCHID Generation
Algorithm (OGA) field in the ORCHID. With the HIT Suite ID in the
OGA ID field, a host can tell, from another host's HIT, whether it
supports the necessary hash and signature algorithms to establish a
HIP association with that host.
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3.2. Generating a HIT from an HI
The HIT MUST be generated according to the ORCHID generation method
described in [RFC7343] using a context ID value of 0xF0EF F02F BFF4
3D0F E793 0C3C 6E61 74EA (this tag value has been generated randomly
by the editor of this specification), and an input that encodes the
Host Identity field (see Section 5.2.9) present in a HIP payload
packet. The set of hash function, signature algorithm, and the
algorithm used for generating the HIT from the HI depends on the HIT
Suite (see Section 5.2.10) and is indicated by the four bits of the
OGA ID field in the ORCHID. Currently, truncated SHA-1, truncated
SHA-384, and truncated SHA-256 [FIPS.180-4.2012] are defined as
hashes for generating a HIT.
For identities that are either RSA, Digital Signature Algorithm (DSA)
[FIPS.186-4.2013], or Elliptic Curve DSA (ECDSA) public keys, the
ORCHID input consists of the public key encoding as specified for the
Host Identity field of the HOST_ID parameter (see Section 5.2.9).
This document defines four algorithm profiles: RSA, DSA, ECDSA, and
ECDSA_LOW. The ECDSA_LOW profile is meant for devices with low
computational capabilities. Hence, one of the following applies:
The RSA public key is encoded as defined in [RFC3110], Section 2,
taking the exponent length (e_len), exponent (e), and modulus (n)
fields concatenated. The length (n_len) of the modulus (n) can be
determined from the total HI Length and the preceding HI fields
including the exponent (e). Thus, the data that serves as input
for the HIT generation has the same length as the HI. The fields
MUST be encoded in network byte order, as defined in [RFC3110].
The DSA public key is encoded as defined in [RFC2536], Section 2,
taking the fields T, Q, P, G, and Y, concatenated as input. Thus,
the data to be hashed is 1 + 20 + 3 * 64 + 3 * 8 * T octets long,
where T is the size parameter as defined in [RFC2536]. The size
parameter T, affecting the field lengths, MUST be selected as the
minimum value that is long enough to accommodate P, G, and Y. The
fields MUST be encoded in network byte order, as defined in
[RFC2536].
The ECDSA public keys are encoded as defined in Sections 4.2 and 6
of [RFC6090].
In Appendix B, the public key encoding process is illustrated using
pseudo-code.
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4. Protocol Overview
This section is a simplified overview of the HIP protocol operation,
and does not contain all the details of the packet formats or the
packet processing steps. Sections 5 and 6 describe in more detail
the packet formats and packet processing steps, respectively, and are
normative in case of any conflicts with this section.
The protocol number 139 has been assigned by IANA to the Host
Identity Protocol.
The HIP payload (Section 5.1) header could be carried in every IP
datagram. However, since HIP headers are relatively large
(40 bytes), it is desirable to 'compress' the HIP header so that the
HIP header only occurs in control packets used to establish or change
HIP association state. The actual method for header 'compression'
and for matching data packets with existing HIP associations (if any)
is defined in separate documents, describing transport formats and
methods. All HIP implementations MUST implement, at minimum, the ESP
transport format for HIP [RFC7402].
4.1. Creating a HIP Association
By definition, the system initiating a HIP base exchange is the
Initiator, and the peer is the Responder. This distinction is
typically forgotten once the base exchange completes, and either
party can become the Initiator in future communications.
The HIP base exchange serves to manage the establishment of state
between an Initiator and a Responder. The first packet, I1,
initiates the exchange, and the last three packets, R1, I2, and R2,
constitute an authenticated Diffie-Hellman [DIF76] key exchange for
session-key generation. In the first two packets, the hosts agree on
a set of cryptographic identifiers and algorithms that are then used
in and after the exchange. During the Diffie-Hellman key exchange, a
piece of keying material is generated. The HIP association keys are
drawn from this keying material by using a Key Derivation Function
(KDF). If other cryptographic keys are needed, e.g., to be used with
ESP, they are expected to be drawn from the same keying material by
using the KDF.
The Initiator first sends a trigger packet, I1, to the Responder.
The packet contains the HIT of the Initiator and possibly the HIT of
the Responder, if it is known. Moreover, the I1 packet initializes
the negotiation of the Diffie-Hellman group that is used for
generating the keying material. Therefore, the I1 packet contains a
list of Diffie-Hellman Group IDs supported by the Initiator. Note
that in some cases it may be possible to replace this trigger packet
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with some other form of a trigger, in which case the protocol starts
with the Responder sending the R1 packet. In such cases, another
mechanism to convey the Initiator's supported DH groups (e.g., by
using a default group) must be specified.
The second packet, R1, starts the actual authenticated Diffie-Hellman
exchange. It contains a puzzle -- a cryptographic challenge that the
Initiator must solve before continuing the exchange. The level of
difficulty of the puzzle can be adjusted based on the level of trust
with the Initiator, the current load, or other factors. In addition,
the R1 contains the Responder's Diffie-Hellman parameter and lists of
cryptographic algorithms supported by the Responder. Based on these
lists, the Initiator can continue, abort, or restart the base
exchange with a different selection of cryptographic algorithms.
Also, the R1 packet contains a signature that covers selected parts
of the message. Some fields are left outside the signature to
support pre-created R1s.
In the I2 packet, the Initiator MUST display the solution to the
received puzzle. Without a correct solution, the I2 message is
discarded. The I2 packet also contains a Diffie-Hellman parameter
that carries needed information for the Responder. The I2 packet is
signed by the Initiator.
The R2 packet acknowledges the receipt of the I2 packet and completes
the base exchange. The packet is signed by the Responder.
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The base exchange is illustrated below in Figure 1. The term "key"
refers to the Host Identity public key, and "sig" represents a
signature using such a key. The packets contain other parameters not
shown in this figure.
Initiator Responder
I1: DH list
-------------------------->
select precomputed R1
R1: puzzle, DH, key, sig
<-------------------------
check sig remain stateless
solve puzzle
I2: solution, DH, {key}, sig
-------------------------->
compute DH check puzzle
check sig
R2: sig
<--------------------------
check sig compute DH
Figure 1
4.1.1. HIP Puzzle Mechanism
The purpose of the HIP puzzle mechanism is to protect the Responder
from a number of denial-of-service threats. It allows the Responder
to delay state creation until receiving the I2 packet. Furthermore,
the puzzle allows the Responder to use a fairly cheap calculation to
check that the Initiator is "sincere" in the sense that it has
churned enough CPU cycles in solving the puzzle.
The puzzle allows a Responder implementation to completely delay
association-specific state creation until a valid I2 packet is
received. An I2 packet without a valid puzzle solution can be
rejected immediately once the Responder has checked the solution.
The solution can be checked by computing only one hash function, and
invalid solutions can be rejected before state is created, and before
CPU-intensive public-key signature verification and Diffie-Hellman
key generation are performed. By varying the difficulty of the
puzzle, the Responder can frustrate CPU- or memory-targeted DoS
attacks.
The Responder can remain stateless and drop most spoofed I2 packets
because puzzle calculation is based on the Initiator's Host Identity
Tag. The idea is that the Responder has a (perhaps varying) number
of pre-calculated R1 packets, and it selects one of these based on
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the information carried in the I1 packet. When the Responder then
later receives the I2 packet, it can verify that the puzzle has been
solved using the Initiator's HIT. This makes it impractical for the
attacker to first exchange one I1/R1 packet, and then generate a
large number of spoofed I2 packets that seemingly come from different
HITs. This method does not protect the Responder from an attacker
that uses fixed HITs, though. Against such an attacker, a viable
approach may be to create a piece of local state, and remember that
the puzzle check has previously failed. See Appendix A for one
possible implementation. Responder implementations SHOULD include
sufficient randomness in the puzzle values so that algorithmic
complexity attacks become impossible [CRO03].
The Responder can set the puzzle difficulty for the Initiator, based
on its level of trust of the Initiator. Because the puzzle is not
included in the signature calculation, the Responder can use
pre-calculated R1 packets and include the puzzle just before sending
the R1 to the Initiator. The Responder SHOULD use heuristics to
determine when it is under a denial-of-service attack, and set the
puzzle difficulty value #K appropriately, as explained later.
4.1.2. Puzzle Exchange
The Responder starts the puzzle exchange when it receives an I1
packet. The Responder supplies a random number #I, and requires the
Initiator to find a number #J. To select a proper #J, the Initiator
must create the concatenation of #I, the HITs of the parties, and #J,
and calculate a hash over this concatenation using the RHASH
algorithm. The lowest-order #K bits of the result MUST be zeros.
The value #K sets the difficulty of the puzzle.
To generate a proper number #J, the Initiator will have to generate a
number of #Js until one produces the hash target of zeros. The
Initiator SHOULD give up after exceeding the puzzle Lifetime in the
PUZZLE parameter (as described in Section 5.2.4). The Responder
needs to re-create the concatenation of #I, the HITs, and the
provided #J, and compute the hash once to prove that the Initiator
completed its assigned task.
To prevent precomputation attacks, the Responder MUST select the
number #I in such a way that the Initiator cannot guess it.
Furthermore, the construction MUST allow the Responder to verify that
the value #I was indeed selected by it and not by the Initiator. See
Appendix A for an example on how to implement this.
Using the Opaque data field in the PUZZLE (see Section 5.2.4) in an
ECHO_REQUEST_SIGNED (see Section 5.2.20) or in an
ECHO_REQUEST_UNSIGNED parameter (see Section 5.2.21), the Responder
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can include some data in R1 that the Initiator MUST copy unmodified
in the corresponding I2 packet. The Responder can use the opaque
data to transfer a piece of local state information to the Initiator
and back -- for example, to recognize that the I2 is a response to a
previously sent R1. The Responder can generate the opaque data in
various ways, e.g., using encryption or hashing with some secret, the
sent #I, and possibly using other related data. With the same
secret, the received #I (from the I2 packet), and the other related
data (if any), the Responder can verify that it has itself sent the
#I to the Initiator. The Responder MUST periodically change such a
secret.
It is RECOMMENDED that the Responder generates new secrets for the
puzzle and new R1s once every few minutes. Furthermore, it is
RECOMMENDED that the Responder is able to verify a valid puzzle
solution at least Lifetime seconds after the puzzle secret has been
deprecated. This time value guarantees that the puzzle is valid for
at least Lifetime and at most 2 * Lifetime seconds. This limits the
usability that an old, solved puzzle has to an attacker. Moreover,
it avoids problems with the validity of puzzles if the lifetime is
relatively short compared to the network delay and the time for
solving the puzzle.
The puzzle value #I and the solution #J are inputs for deriving the
keying material from the Diffie-Hellman key exchange (see
Section 6.5). Therefore, to ensure that the derived keying material
differs, a Responder SHOULD NOT use the same puzzle #I with the same
DH keys for the same Initiator twice. Such uniqueness can be
achieved, for example, by using a counter as an additional input for
generating #I. This counter can be increased for each processed I1
packet. The state of the counter can be transmitted in the Opaque
data field in the PUZZLE (see Section 5.2.4), in an
ECHO_REQUEST_SIGNED parameter (see Section 5.2.20), or in an
ECHO_REQUEST_UNSIGNED parameter (see Section 5.2.21) without the need
to establish state.
NOTE: The protocol developers explicitly considered whether R1 should
include a timestamp in order to protect the Initiator from replay
attacks. The decision was to NOT include a timestamp, to avoid
problems with global time synchronization.
NOTE: The protocol developers explicitly considered whether a memory-
bound function should be used for the puzzle instead of a CPU-bound
function. The decision was to not use memory-bound functions.
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4.1.3. Authenticated Diffie-Hellman Protocol with DH Group Negotiation
The packets R1, I2, and R2 implement a standard authenticated
Diffie-Hellman exchange. The Responder sends one of its public
Diffie-Hellman keys and its public authentication key, i.e., its Host
Identity, in R1. The signature in the R1 packet allows the Initiator
to verify that the R1 has been once generated by the Responder.
However, since the R1 is precomputed and therefore does not cover
association-specific information in the I1 packet, it does not
protect against replay attacks.
Before the actual authenticated Diffie-Hellman exchange, the
Initiator expresses its preference regarding its choice of the DH
groups in the I1 packet. The preference is expressed as a sorted
list of DH Group IDs. The I1 packet is not protected by a signature.
Therefore, this list is sent in an unauthenticated way to avoid
costly computations for processing the I1 packet at the Responder
side. Based on the preferences of the Initiator, the Responder sends
an R1 packet containing its most suitable public DH value. The
Responder also attaches a list of its own preferences to the R1 to
convey the basis for the DH group selection to the Initiator. This
list is carried in the signed part of the R1 packet. If the choice
of the DH group value in the R1 does not match the preferences of the
Initiator and the Responder, the Initiator can detect that the list
of DH Group IDs in the I1 was manipulated (see below for details).
If none of the DH Group IDs in the I1 packet are supported by the
Responder, the Responder selects the DH group most suitable for it,
regardless of the Initiator's preference. It then sends the R1
containing this DH group and its list of supported DH Group IDs to
the Initiator.
When the Initiator receives an R1, it receives one of the Responder's
public Diffie-Hellman values and the list of DH Group IDs supported
by the Responder. This list is covered by the signature in the R1
packet to avoid forgery. The Initiator compares the Group ID of the
public DH value in the R1 packet to the list of supported DH Group
IDs in the R1 packets and to its own preferences expressed in the
list of supported DH Group IDs. The Initiator continues the BEX only
if the Group ID of the public DH value of the Responder is the most
preferred of the IDs supported by both the Initiator and Responder.
Otherwise, the communication is subject to a downgrade attack, and
the Initiator MUST either restart the base exchange with a new I1
packet or abort the base exchange. If the Responder's choice of the
DH group is not supported by the Initiator, the Initiator MAY abort
the handshake or send a new I1 packet with a different list of
supported DH groups. However, the Initiator MUST verify the
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signature of the R1 packet before restarting or aborting the
handshake. It MUST silently ignore the R1 packet if the signature is
not valid.
If the preferences regarding the DH Group ID match, the Initiator
computes the Diffie-Hellman session key (Kij). The Initiator creates
a HIP association using keying material from the session key (see
Section 6.5) and may use the HIP association to encrypt its public
authentication key, i.e., the Host Identity. The resulting I2 packet
contains the Initiator's Diffie-Hellman key and its (optionally
encrypted) public authentication key. The signature of the I2
message covers all parameters of the signed parameter ranges (see
Section 5.2) in the packet without exceptions, as in the R1.
The Responder extracts the Initiator's Diffie-Hellman public key from
the I2 packet, computes the Diffie-Hellman session key, creates a
corresponding HIP association, and decrypts the Initiator's public
authentication key. It can then verify the signature using the
authentication key.
The final message, R2, completes the BEX and protects the Initiator
against replay attacks, because the Responder uses the shared key
from the Diffie-Hellman exchange to create a Hashed Message
Authentication Code (HMAC) and also uses the private key of its Host
Identity to sign the packet contents.
4.1.4. HIP Replay Protection
HIP includes the following mechanisms to protect against malicious
packet replays. Responders are protected against replays of I1
packets by virtue of the stateless response to I1 packets with
pre-signed R1 messages. Initiators are protected against R1 replays
by a monotonically increasing "R1 generation counter" included in
the R1. Responders are protected against replays of forged I2
packets by the puzzle mechanism (see Section 4.1.1 above), and
optional use of opaque data. Hosts are protected against replays of
R2 packets and UPDATEs by use of a less expensive HMAC verification
preceding the HIP signature verification.
The R1 generation counter is a monotonically increasing 64-bit
counter that may be initialized to any value. The scope of the
counter MAY be system-wide, but there SHOULD be a separate counter
for each Host Identity, if there is more than one local Host
Identity. The value of this counter SHOULD be preserved across
system reboots and invocations of the HIP base exchange. This
counter indicates the current generation of puzzles. Implementations
MUST accept puzzles from the current generation and MAY accept
puzzles from earlier generations. A system's local counter MUST be
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incremented at least as often as every time old R1s cease to be
valid. The local counter SHOULD never be decremented; otherwise, the
host exposes its peers to the replay of previously generated, higher-
numbered R1s.
A host may receive more than one R1, either due to sending multiple
I1 packets (see Section 6.6.1) or due to a replay of an old R1. When
sending multiple I1 packets to the same host, an Initiator SHOULD
wait for a small amount of time (a reasonable time may be
2 * expected RTT) after the first R1 reception to allow possibly
multiple R1s to arrive, and it SHOULD respond to an R1 among the set
with the largest R1 generation counter. If an Initiator is
processing an R1 or has already sent an I2 packet (still waiting for
the R2 packet) and it receives another R1 with a larger R1 generation
counter, it MAY elect to restart R1 processing with the fresher R1,
as if it were the first R1 to arrive.
The R1 generation counter may roll over or may become reset. It is
important for an Initiator to be robust to the loss of state about
the R1 generation counter of a peer or to a reset of the peer's
counter. It is recommended that, when choosing between multiple R1s,
the Initiator prefer to use the R1 that corresponds to the current R1
generation counter, but that if it is unable to make progress with
that R1, the Initiator may try the other R1s, beginning with the R1
packet with the highest counter.
4.1.5. Refusing a HIP Base Exchange
A HIP-aware host may choose not to accept a HIP base exchange. If
the host's policy is to only be an Initiator and policy allows the
establishment of a HIP association with the original Initiator, it
should begin its own HIP base exchange. A host MAY choose to have
such a policy since only the privacy of the Initiator's HI is
protected in the exchange. It should be noted that such behavior can
introduce the risk of a race condition if each host's policy is to
only be an Initiator, at which point the HIP base exchange will fail.
If the host's policy does not permit it to enter into a HIP exchange
with the Initiator, it should send an ICMP 'Destination Unreachable,
Administratively Prohibited' message. A more complex HIP packet is
not used here as it actually opens up more potential DoS attacks than
a simple ICMP message. A HIP NOTIFY message is not used because no
HIP association exists between the two hosts at that time.
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4.1.6. Aborting a HIP Base Exchange
Two HIP hosts may encounter situations in which they cannot complete
a HIP base exchange because of insufficient support for cryptographic
algorithms, in particular the HIT Suites and DH groups. After
receiving the R1 packet, the Initiator can determine whether the
Responder supports the required cryptographic operations to
successfully establish a HIP association. The Initiator can abort
the BEX silently after receiving an R1 packet that indicates an
unsupported set of algorithms. The specific conditions are described
below.
The R1 packet contains a signed list of HIT Suite IDs as supported by
the Responder. Therefore, the Initiator can determine whether its
source HIT is supported by the Responder. If the HIT Suite ID of the
Initiator's HIT is not contained in the list of HIT Suites in the R1,
the Initiator MAY abort the handshake silently or MAY restart the
handshake with a new I1 packet that contains a source HIT supported
by the Responder.
During the handshake, the Initiator and the Responder agree on a
single DH group. The Responder selects the DH group and its DH
public value in the R1 based on the list of DH Group IDs in the I1
packet. If the Responder supports none of the DH groups requested by
the Initiator, the Responder selects an arbitrary DH and replies with
an R1 containing its list of supported DH Group IDs. In such a case,
the Initiator receives an R1 packet containing the DH public value
for an unrequested DH group and also the Responder's DH group list in
the signed part of the R1 packet. At this point, the Initiator MAY
abort the handshake or MAY restart the handshake by sending a new I1
packet containing a selection of DH Group IDs that is supported by
the Responder.
4.1.7. HIP Downgrade Protection
In a downgrade attack, an attacker attempts to unnoticeably
manipulate the packets of an Initiator and/or a Responder to
influence the result of the cryptographic negotiations in the BEX in
its favor. As a result, the victims select weaker cryptographic
algorithms than they would otherwise have selected without the
attacker's interference. Downgrade attacks can only be successful if
they remain undetected by the victims and the victims falsely assume
a secure communication channel.
In HIP, almost all packet parameters related to cryptographic
negotiations are covered by signatures. These parameters cannot be
directly manipulated in a downgrade attack without invalidating the
signature. However, signed packets can be subject to replay attacks.
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In such a replay attack, the attacker could use an old BEX packet
with an outdated and weak selection of cryptographic algorithms and
replay it instead of a more recent packet with a collection of
stronger cryptographic algorithms. Signed packets that could be
subject to this replay attack are the R1 and I2 packet. However,
replayed R1 and I2 packets cannot be used to successfully establish a
HIP BEX because these packets also contain the public DH values of
the Initiator and the Responder. Old DH values from replayed packets
lead to invalid keying material and mismatching shared secrets
because the attacker is unable to derive valid keying material from
the DH public keys in the R1 and cannot generate a valid HMAC and
signature for a replayed I2.
In contrast to the first version of HIP [RFC5201], version 2 of HIP
as defined in this document begins the negotiation of the DH groups
already in the first BEX packet, the I1. The I1 packet is, by
intention, not protected by a signature, to avoid CPU-intensive
cryptographic operations processing floods of I1 packets targeted at
the Responder. Hence, the list of DH Group IDs in the I1 packet is
vulnerable to forgery and manipulation. To thwart an unnoticed
manipulation of the I1 packet, the Responder chooses the DH group
deterministically and includes its own list of DH Group IDs in the
signed part of the R1 packet. The Initiator can detect an attempted
downgrade attack by comparing the list of DH Group IDs in the R1
packet to its own preferences in the I1 packet. If the choice of the
DH group in the R1 packet does not equal the best match of the two
lists (the highest-priority DH ID of the Responder that is present in
the Initiator's DH list), the Initiator can conclude that its list in
the I1 packet was altered by an attacker. In this case, the
Initiator can restart or abort the BEX. As mentioned before, the
detection of the downgrade attack is sufficient to prevent it.
4.1.8. HIP Opportunistic Mode
It is possible to initiate a HIP BEX even if the Responder's HI (and
HIT) is unknown. In this case, the initial I1 packet contains all
zeros as the destination HIT. This kind of connection setup is
called opportunistic mode.
The Responder may have multiple HITs due to multiple supported HIT
Suites. Since the Responder's HIT Suite in the opportunistic mode is
not determined by the destination HIT of the I1 packet, the Responder
can freely select a HIT of any HIT Suite. The complete set of HIT
Suites supported by the Initiator is not known to the Responder.
Therefore, the Responder SHOULD select its HIT from the same HIT
Suite as the Initiator's HIT (indicated by the HIT Suite information
in the OGA ID field of the Initiator's HIT) because this HIT Suite is
obviously supported by the Initiator. If the Responder selects a
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different HIT that is not supported by the Initiator, the Initiator
MAY restart the BEX with an I1 packet with a source HIT that is
contained in the list of the Responder's HIT Suites in the R1 packet.
Note that the Initiator cannot verify the signature of the R1 packet
if the Responder's HIT Suite is not supported. Therefore, the
Initiator MUST treat R1 packets with unsupported Responder HITs as
potentially forged and MUST NOT use any parameters from the
unverified R1 besides the HIT_SUITE_LIST. Moreover, an Initiator
that uses an unverified HIT_SUITE_LIST from an R1 packet to determine
a possible source HIT MUST verify that the HIT_SUITE_LIST in the
first unverified R1 packet matches the HIT_SUITE_LIST in the second
R1 packet for which the Initiator supports the signature algorithm.
The Initiator MUST restart the BEX with a new I1 packet for which the
algorithm was mentioned in the verifiable R1 if the two lists do not
match. This procedure is necessary to mitigate downgrade attacks.
There are both security and API issues involved with the
opportunistic mode. These issues are described in the remainder of
this section.
Given that the Responder's HI is not known by the Initiator, there
must be suitable API calls that allow the Initiator to request,
directly or indirectly, that the underlying system initiates the HIP
base exchange solely based on locators. The Responder's HI will be
tentatively available in the R1 packet, and in an authenticated form
once the R2 packet has been received and verified. Hence, the
Responder's HIT could be communicated to the application via new API
mechanisms. However, with a backwards-compatible API the application
sees only the locators used for the initial contact. Depending on
the desired semantics of the API, this can raise the following
issues:
o The actual locators may later change if an UPDATE message is used,
even if from the API perspective the association still appears to
be between two specific locators. However, the locator update is
still secure, and the association is still between the same nodes.
o Different associations between the same two locators may result in
connections to different nodes, if the implementation no longer
remembers which identifier the peer had in an earlier association.
This is possible when the peer's locator has changed for
legitimate reasons or when an attacker pretends to be a node that
has the peer's locator. Therefore, when using opportunistic mode,
HIP implementations MUST NOT place any expectation that the peer's
HI returned in the R1 message matches any HI previously seen from
that address.
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If the HIP implementation and application do not have the same
understanding of what constitutes an association, this may even
happen within the same association. For instance, an
implementation may not know when HIP state can be purged for
UDP-based applications.
In addition, the following security considerations apply. The
generation counter mechanism will be less efficient in protecting
against replays of the R1 packet, given that the Responder can choose
a replay that uses an arbitrary HI, not just the one given in the I1
packet.
More importantly, the opportunistic exchange is vulnerable to
man-in-the-middle attacks, because the Initiator does not have any
public key information about the peer. To assess the impacts of this
vulnerability, we compare it to vulnerabilities in current,
non-HIP-capable communications.
An attacker on the path between the two peers can insert itself as a
man-in-the-middle by providing its own identifier to the Initiator
and then initiating another HIP association towards the Responder.
For this to be possible, the Initiator must employ opportunistic
mode, and the Responder must be configured to accept a connection
from any HIP-enabled node.
An attacker outside the path will be unable to do so, given that it
cannot respond to the messages in the base exchange.
These security properties are characteristic also of communications
in the current Internet. A client contacting a server without
employing end-to-end security may find itself talking to the server
via a man-in-the-middle, assuming again that the server is willing to
talk to anyone.
If end-to-end security is in place, then the worst that can happen in
both the opportunistic HIP and non-HIP (normal IP) cases is denial-
of-service; an entity on the path can disrupt communications, but
will be unable to successfully insert itself as a man-in-the-middle.
However, once the opportunistic exchange has successfully completed,
HIP provides confidentiality and integrity protection for the
communications, and can securely change the locators of the
endpoints.
As a result, opportunistic mode in HIP offers a "better than nothing"
security model. Initially, a base exchange authenticated in the
opportunistic mode involves a leap of faith subject to man-in-the-
middle attacks, but subsequent datagrams related to the same HIP
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association cannot be compromised by a new man-in-the-middle attack.
Further, if the man-in-the-middle moves away from the path of the
active association, the attack would be exposed after the fact.
Thus, it can be stated that opportunistic mode in HIP is at least as
secure as unprotected IP-based communications.
4.2. Updating a HIP Association
A HIP association between two hosts may need to be updated over time.
Examples include the need to rekey expiring security associations,
add new security associations, or change IP addresses associated with
hosts. The UPDATE packet is used for those and other similar
purposes. This document only specifies the UPDATE packet format and
basic processing rules, with mandatory parameters. The actual usage
is defined in separate specifications.
HIP provides a general-purpose UPDATE packet, which can carry
multiple HIP parameters, for updating the HIP state between two
peers. The UPDATE mechanism has the following properties:
UPDATE messages carry a monotonically increasing sequence number
and are explicitly acknowledged by the peer. Lost UPDATEs or
acknowledgments may be recovered via retransmission. Multiple
UPDATE messages may be outstanding under certain circumstances.
UPDATE is protected by both HIP_MAC and HIP_SIGNATURE parameters,
since processing UPDATE signatures alone is a potential DoS attack
against intermediate systems.
UPDATE packets are explicitly acknowledged by the use of an
acknowledgment parameter that echoes an individual sequence number
received from the peer. A single UPDATE packet may contain both a
sequence number and one or more acknowledgment numbers (i.e.,
piggybacked acknowledgment(s) for the peer's UPDATE).
The UPDATE packet is defined in Section 5.3.5.
4.3. Error Processing
HIP error processing behavior depends on whether or not there exists
an active HIP association. In general, if a HIP association exists
between the sender and receiver of a packet causing an error
condition, the receiver SHOULD respond with a NOTIFY packet. On the
other hand, if there are no existing HIP associations between the
sender and receiver, or the receiver cannot reasonably determine the
identity of the sender, the receiver MAY respond with a suitable ICMP
message; see Section 5.4 for more details.
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The HIP protocol and state machine are designed to recover from one
of the parties crashing and losing its state. The following
scenarios describe the main use cases covered by the design.
No prior state between the two systems.
The system with data to send is the Initiator. The process
follows the standard four-packet base exchange, establishing
the HIP association.
The system with data to send has no state with the receiver, but
the receiver has a residual HIP association.
The system with data to send is the Initiator. The Initiator
acts as in no prior state, sending an I1 packet and receiving
an R1 packet. When the Responder receives a valid I2 packet,
the old association is 'discovered' and deleted, and the new
association is established.
The system with data to send has a HIP association, but the
receiver does not.
The system sends data on the outbound user data security
association. The receiver 'detects' the situation when it
receives a user data packet that it cannot match to any HIP
association. The receiving host MUST discard this packet.
The receiving host SHOULD send an ICMP packet, with the type
Parameter Problem, to inform the sender that the HIP
association does not exist (see Section 5.4), and it MAY
initiate a new HIP BEX. However, responding with these
optional mechanisms is implementation or policy dependent. If
the sending application doesn't expect a response, the system
could possibly send a large number of packets in this state, so
for this reason, the sending of one or more ICMP packets is
RECOMMENDED. However, any such responses MUST be rate-limited
to prevent abuse (see Section 5.4).
4.4. HIP State Machine
HIP itself has little state. In the HIP base exchange, there is an
Initiator and a Responder. Once the security associations (SAs) are
established, this distinction is lost. If the HIP state needs to be
re-established, the controlling parameters are which peer still has
state and which has a datagram to send to its peer. The following
state machine attempts to capture these processes.
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The state machine is symmetric and is presented in a single system
view, representing either an Initiator or a Responder. The state
machine is not a full representation of the processing logic.
Additional processing rules are presented in the packet definitions.
Hence, both are needed to completely implement HIP.
This document extends the state machine as defined in [RFC5201] and
introduces a restart option to allow for the negotiation of
cryptographic algorithms. The extension to the previous state
machine in [RFC5201] is a transition from state I1-SENT back again to
I1-SENT; namely, the restart option. An Initiator is required to
restart the HIP base exchange if the Responder does not support the
HIT Suite of the Initiator. In this case, the Initiator restarts the
HIP base exchange by sending a new I1 packet with a source HIT
supported by the Responder.
Implementors must understand that the state machine, as described
here, is informational. Specific implementations are free to
implement the actual processing logic differently. Section 6
describes the packet processing rules in more detail. This state
machine focuses on the HIP I1, R1, I2, and R2 packets only. New
states and state transitions may be introduced by mechanisms in other
specifications (such as mobility and multihoming).
4.4.1. State Machine Terminology
Unused Association Lifetime (UAL): Implementation-specific time for
which, if no packet is sent or received for this time interval, a
host MAY begin to tear down an active HIP association.
Maximum Segment Lifetime (MSL): Maximum time that a HIP packet is
expected to spend in the network. A default value of 2 minutes
has been borrowed from [RFC0793] because it is a prevailing
assumption for packet lifetimes.
Exchange Complete (EC): Time that the host spends at the R2-SENT
state before it moves to the ESTABLISHED state. The time is n *
I2 retransmission timeout, where n is about I2_RETRIES_MAX.
Receive ANYOTHER: Any received packet for which no state transitions
or processing rules are defined for a given state.
Moskowitz, et al. Standards Track [Page 26]
RFC 7401 HIPv2 April 2015
4.4.2. HIP States
+---------------------+---------------------------------------------+
| State | Explanation |
+---------------------+---------------------------------------------+
| UNASSOCIATED | State machine start |
| | |
| I1-SENT | Initiating base exchange |
| | |
| I2-SENT | Waiting to complete base exchange |
| | |
| R2-SENT | Waiting to complete base exchange |
| | |
| ESTABLISHED | HIP association established |
| | |
| CLOSING | HIP association closing, no data can be |
| | sent |
| | |
| CLOSED | HIP association closed, no data can be sent |
| | |
| E-FAILED | HIP base exchange failed |
+---------------------+---------------------------------------------+
Table 1: HIP States
Moskowitz, et al. Standards Track [Page 27]
RFC 7401 HIPv2 April 2015
4.4.3. HIP State Processes
System behavior in state UNASSOCIATED, Table 2.
+----------------------------+--------------------------------------+
| Trigger | Action |
+----------------------------+--------------------------------------+
| User data to send, | Send I1 and go to I1-SENT |
| requiring a new HIP | |
| association | |
| | |
| Receive I1 | Send R1 and stay at UNASSOCIATED |
| | |
| Receive I2, process | If successful, send R2 and go to |
| | R2-SENT |
| | |
| | If fail, stay at UNASSOCIATED |
| | |
| Receive user data for an | Optionally send ICMP as defined in |
| unknown HIP association | Section 5.4 and stay at UNASSOCIATED |
| | |
| Receive CLOSE | Optionally send ICMP Parameter |
| | Problem and stay at UNASSOCIATED |
| | |
| Receive ANYOTHER | Drop and stay at UNASSOCIATED |
+----------------------------+--------------------------------------+
Table 2: UNASSOCIATED - Start State
Moskowitz, et al. Standards Track [Page 28]
RFC 7401 HIPv2 April 2015
System behavior in state I1-SENT, Table 3.
+---------------------+---------------------------------------------+
| Trigger | Action |
+---------------------+---------------------------------------------+
| Receive I1 from | If the local HIT is smaller than the peer |
| Responder | HIT, drop I1 and stay at I1-SENT (see |
| | Section 6.5 for HIT comparison) |
| | |
| | If the local HIT is greater than the peer |
| | HIT, send R1 and stay at I1-SENT |
| | |
| Receive I2, process | If successful, send R2 and go to R2-SENT |
| | |
| | If fail, stay at I1-SENT |
| | |
| Receive R1, process | If the HIT Suite of the local HIT is not |
| | supported by the peer, select supported |
| | local HIT, send I1, and stay at I1-SENT |
| | |
| | If successful, send I2 and go to I2-SENT |
| | |
| | If fail, stay at I1-SENT |
| | |
| Receive ANYOTHER | Drop and stay at I1-SENT |
| | |
| Timeout | Increment trial counter |
| | |
| | If counter is less than I1_RETRIES_MAX, |
| | send I1 and stay at I1-SENT |
| | |
| | If counter is greater than I1_RETRIES_MAX, |
| | go to E-FAILED |
+---------------------+---------------------------------------------+
Table 3: I1-SENT - Initiating the HIP Base Exchange
Moskowitz, et al. Standards Track [Page 29]
RFC 7401 HIPv2 April 2015
System behavior in state I2-SENT, Table 4.
+---------------------+---------------------------------------------+
| Trigger | Action |
+---------------------+---------------------------------------------+
| Receive I1 | Send R1 and stay at I2-SENT |
| | |
| Receive R1, process | If successful, send I2 and stay at I2-SENT |
| | |
| | If fail, stay at I2-SENT |
| | |
| Receive I2, process | If successful and local HIT is smaller than |
| | the peer HIT, drop I2 and stay at I2-SENT |
| | |
| | If successful and local HIT is greater than |
| | the peer HIT, send R2 and go to R2-SENT |
| | |
| | If fail, stay at I2-SENT |
| | |
| Receive R2, process | If successful, go to ESTABLISHED |
| | |
| | If fail, stay at I2-SENT |
| | |
| Receive CLOSE, | If successful, send CLOSE_ACK and go to |
| process | CLOSED |
| | |
| | If fail, stay at I2-SENT |
| | |
| Receive ANYOTHER | Drop and stay at I2-SENT |
| | |
| Timeout | Increment trial counter |
| | |
| | If counter is less than I2_RETRIES_MAX, |
| | send I2 and stay at I2-SENT |
| | |
| | If counter is greater than I2_RETRIES_MAX, |
| | go to E-FAILED |
+---------------------+---------------------------------------------+
Table 4: I2-SENT - Waiting to Finish the HIP Base Exchange
Moskowitz, et al. Standards Track [Page 30]
RFC 7401 HIPv2 April 2015
System behavior in state R2-SENT, Table 5.
+------------------------+------------------------------------------+
| Trigger | Action |
+------------------------+------------------------------------------+
| Receive I1 | Send R1 and stay at R2-SENT |
| | |
| Receive I2, process | If successful, send R2 and stay at |
| | R2-SENT |
| | |
| | If fail, stay at R2-SENT |
| | |
| Receive R1 | Drop and stay at R2-SENT |
| | |
| Receive R2 | Drop and stay at R2-SENT |
| | |
| Receive data or UPDATE | Move to ESTABLISHED |
| | |
| Exchange Complete | Move to ESTABLISHED |
| Timeout | |
| | |
| Receive CLOSE, process | If successful, send CLOSE_ACK and go to |
| | CLOSED |
| | |
| | If fail, stay at ESTABLISHED |
| | |
| Receive CLOSE_ACK | Drop and stay at R2-SENT |
| | |
| Receive NOTIFY | Process and stay at R2-SENT |
+------------------------+------------------------------------------+
Table 5: R2-SENT - Waiting to Finish HIP
Moskowitz, et al. Standards Track [Page 31]
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System behavior in state ESTABLISHED, Table 6.
+---------------------+---------------------------------------------+
| Trigger | Action |
+---------------------+---------------------------------------------+
| Receive I1 | Send R1 and stay at ESTABLISHED |
| | |
| Receive I2 | Process with puzzle and possible Opaque |
| | data verification |
| | |
| | If successful, send R2, drop old HIP |
| | association, establish a new HIP |
| | association, and go to R2-SENT |
| | |
| | If fail, stay at ESTABLISHED |
| | |
| Receive R1 | Drop and stay at ESTABLISHED |
| | |
| Receive R2 | Drop and stay at ESTABLISHED |
| | |
| Receive user data | Process and stay at ESTABLISHED |
| for HIP association | |
| | |
| No packet | Send CLOSE and go to CLOSING |
| sent/received | |
| during UAL minutes | |
| | |
| Receive UPDATE | Process and stay at ESTABLISHED |
| | |
| Receive CLOSE, | If successful, send CLOSE_ACK and go to |
| process | CLOSED |
| | |
| | If fail, stay at ESTABLISHED |
| | |
| Receive CLOSE_ACK | Drop and stay at ESTABLISHED |
| | |
| Receive NOTIFY | Process and stay at ESTABLISHED |
+---------------------+---------------------------------------------+
Table 6: ESTABLISHED - HIP Association Established
Moskowitz, et al. Standards Track [Page 32]
RFC 7401 HIPv2 April 2015
System behavior in state CLOSING, Table 7.
+----------------------------+--------------------------------------+
| Trigger | Action |
+----------------------------+--------------------------------------+
| User data to send, | Send I1 and go to I1-SENT |
| requires the creation of | |
| another incarnation of the | |
| HIP association | |
| | |
| Receive I1 | Send R1 and stay at CLOSING |
| | |
| Receive I2, process | If successful, send R2 and go to |
| | R2-SENT |
| | |
| | If fail, stay at CLOSING |
| | |
| Receive R1, process | If successful, send I2 and go to |
| | I2-SENT |
| | |
| | If fail, stay at CLOSING |
| | |
| Receive CLOSE, process | If successful, send CLOSE_ACK, |
| | discard state, and go to CLOSED |
| | |
| | If fail, stay at CLOSING |
| | |
| Receive CLOSE_ACK, process | If successful, discard state and go |
| | to UNASSOCIATED |
| | |
| | If fail, stay at CLOSING |
| | |
| Receive ANYOTHER | Drop and stay at CLOSING |
| | |
| Timeout | Increment timeout sum and reset |
| | timer. If timeout sum is less than |
| | UAL+MSL minutes, retransmit CLOSE |
| | and stay at CLOSING. |
| | |
| | If timeout sum is greater than |
| | UAL+MSL minutes, go to UNASSOCIATED |
+----------------------------+--------------------------------------+
Table 7: CLOSING - HIP Association Has Not Been Used for UAL Minutes
Moskowitz, et al. Standards Track [Page 33]
RFC 7401 HIPv2 April 2015
System behavior in state CLOSED, Table 8.
+----------------------------------------+--------------------------+
| Trigger | Action |
+----------------------------------------+--------------------------+
| Datagram to send, requires the | Send I1 and stay at |
| creation of another incarnation of the | CLOSED |
| HIP association | |
| | |
| Receive I1 | Send R1 and stay at |
| | CLOSED |
| | |
| Receive I2, process | If successful, send R2 |
| | and go to R2-SENT |
| | |
| | If fail, stay at CLOSED |
| | |
| Receive R1, process | If successful, send I2 |
| | and go to I2-SENT |
| | |
| | If fail, stay at CLOSED |
| | |
| Receive CLOSE, process | If successful, send |
| | CLOSE_ACK and stay at |
| | CLOSED |
| | |
| | If fail, stay at CLOSED |
| | |
| Receive CLOSE_ACK, process | If successful, discard |
| | state and go to |
| | UNASSOCIATED |
| | |
| | If fail, stay at CLOSED |
| | |
| Receive ANYOTHER | Drop and stay at CLOSED |
| | |
| Timeout (UAL+2MSL) | Discard state and go to |
| | UNASSOCIATED |
+----------------------------------------+--------------------------+
Table 8: CLOSED - CLOSE_ACK Sent, Resending CLOSE_ACK if Necessary
Moskowitz, et al. Standards Track [Page 34]
RFC 7401 HIPv2 April 2015
System behavior in state E-FAILED, Table 9.
+-------------------------+-----------------------------------------+
| Trigger | Action |
+-------------------------+-----------------------------------------+
| Wait for | Go to UNASSOCIATED. Renegotiation is |
| implementation-specific | possible after moving to UNASSOCIATED |
| time | state. |
+-------------------------+-----------------------------------------+
Table 9: E-FAILED - HIP Failed to Establish Association with Peer
4.4.4. Simplified HIP State Diagram
The following diagram (Figure 2) shows the major state transitions.
Transitions based on received packets implicitly assume that the
packets are successfully authenticated or processed.
Moskowitz, et al. Standards Track [Page 35]
RFC 7401 HIPv2 April 2015
+--+ +----------------------------+
recv I1, send R1 | | | |
| v v |
+--------------+ recv I2, send R2 |
+----------------| UNASSOCIATED |----------------+ |
datagram | +--+ +--------------+ | |
to send, | | | Alg. not supported, | |
send I1 | | | send I1 | |
. v | v | |
. +---------+ recv I2, send R2 | |
+---->| I1-SENT |--------------------------------------+ | |
| +---------+ +----------------------+ | | |
| | recv R2, | recv I2, send R2 | | | |
| v send I2 | v v v |
| +---------+ | +---------+ |
| +--->| I2-SENT |----------+ +--------------| R2-SENT |<---+ |
| | +---------+ | +---------+ | |
| | | |recv R2 | data or| | |
| |recv R1, | | | EC timeout| | |
| |send I2 +--|-----------------+ | receive I2,| |
| | | | +-------------+ | send R2| |
| | | +------>| ESTABLISHED |<----------+ | |
| | | +-------------+ | |
| | | | | | receive I2, send R2 | |
| | +------------+ | +-------------------------------+ |
| | | +-----------+ | |
| | | no packet sent/received| +---+ | |
| | | for UAL min, send CLOSE| | |timeout | |
| | | v v |(UAL+MSL) | |
| | | +---------+ |retransmit | |
+--|----------|------------------------| CLOSING |-+CLOSE | |
| | +---------+ | |
| | | | | | | |
+----------|-------------------------+ | | +----------------+ |
| | +-----------+ +------------------|--+
| | |recv CLOSE, recv CLOSE_ACK | |
| +-------------+ |send CLOSE_ACK or timeout | |
| recv CLOSE, | | (UAL+MSL) | |
| send CLOSE_ACK v v | |
| +--------+ receive I2, send R2 | |
+---------------------| CLOSED |------------------------------+ |
+--------+ |
^ | | |
recv CLOSE, send CLOSE_ACK| | | timeout (UAL+2MSL) |
+-+ +------------------------------------+
Figure 2
Moskowitz, et al. Standards Track [Page 36]
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4.5. User Data Considerations
4.5.1. TCP and UDP Pseudo Header Computation for User Data
When computing TCP and UDP checksums on user data packets that flow
through sockets bound to HITs, the IPv6 pseudo header format
[RFC2460] MUST be used, even if the actual addresses in the header of
the packet are IPv4 addresses. Additionally, the HITs MUST be used
in place of the IPv6 addresses in the IPv6 pseudo header. Note that
the pseudo header for actual HIP payloads is computed differently;
see Section 5.1.1.
4.5.2. Sending Data on HIP Packets
Other documents may define how to include user data in various HIP
packets. However, currently the HIP header is a terminal header, and
not followed by any other headers.
4.5.3. Transport Formats
The actual data transmission format, used for user data after the HIP
base exchange, is not defined in this document. Such transport
formats and methods are described in separate specifications. All
HIP implementations MUST implement, at minimum, the ESP transport
format for HIP [RFC7402]. The transport format to be chosen is
negotiated in the base exchange. The Responder expresses its
preference regarding the transport format in the
TRANSPORT_FORMAT_LIST in the R1 packet, and the Initiator selects one
transport format and adds the respective HIP parameter to the I2
packet.
4.5.4. Reboot, Timeout, and Restart of HIP
Simulating a loss of state is a potential DoS attack. The following
process has been crafted to manage state recovery without presenting
a DoS opportunity.
If a host reboots or the HIP association times out, it has lost its
HIP state. If the host that lost state has a datagram to send to the
peer, it simply restarts the HIP base exchange. After the base
exchange has completed, the Initiator can create a new payload
association and start sending data. The peer does not reset its
state until it receives a valid I2 packet.
If a system receives a user data packet that cannot be matched to any
existing HIP association, it is possible that it has lost the state
and its peer has not. It MAY send an ICMP packet with the Parameter
Problem type, and with the Pointer pointing to the referred
Moskowitz, et al. Standards Track [Page 37]
RFC 7401 HIPv2 April 2015
HIP-related association information. Reacting to such traffic
depends on the implementation and the environment where the
implementation is used.
If the host that apparently has lost its state decides to restart the
HIP base exchange, it sends an I1 packet to the peer. After the base
exchange has been completed successfully, the Initiator can create a
new HIP association, and the peer drops its old payload associations
and creates a new one.
4.6. Certificate Distribution
This document does not define how to use certificates or how to
transfer them between hosts. These functions are expected to be
defined in a future specification, as was done for HIP version 1 (see
[RFC6253]). A parameter type value, meant to be used for carrying
certificates, is reserved, though: CERT, Type 768; see Section 5.2.
5. Packet Formats
5.1. Payload Format
All HIP packets start with a fixed header.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Header | Header Length |0| Packet Type |Version| RES.|1|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Checksum | Controls |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sender's Host Identity Tag (HIT) |
| |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Receiver's Host Identity Tag (HIT) |
| |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
/ HIP Parameters /
/ /
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Moskowitz, et al. Standards Track [Page 38]
RFC 7401 HIPv2 April 2015
The HIP header is logically an IPv6 extension header. However, this
document does not describe processing for Next Header values other
than decimal 59, IPPROTO_NONE, the IPv6 'no next header' value.
Future documents MAY define behavior for other values. However,
current implementations MUST ignore trailing data if an unimplemented
Next Header value is received.
The Header Length field contains the combined length of the HIP
Header and HIP parameters in 8-byte units, excluding the first
8 bytes. Since all HIP headers MUST contain the sender's and
receiver's HIT fields, the minimum value for this field is 4, and
conversely, the maximum length of the HIP Parameters field is
(255 * 8) - 32 = 2008 bytes (see Section 5.1.3 regarding HIP
fragmentation). Note: this sets an additional limit for sizes of
parameters included in the Parameters field, independent of the
individual parameter maximum lengths.
The Packet Type indicates the HIP packet type. The individual packet
types are defined in the relevant sections. If a HIP host receives a
HIP packet that contains an unrecognized packet type, it MUST drop
the packet.
The HIP Version field is four bits. The version defined in this
document is 2. The version number is expected to be incremented only
if there are incompatible changes to the protocol. Most extensions
can be handled by defining new packet types, new parameter types, or
new Controls (see Section 5.1.2).
The following three bits are reserved for future use. They MUST be
zero when sent, and they MUST be ignored when handling a received
packet.
The two fixed bits in the header are reserved for SHIM6 compatibility
[RFC5533], Section 5.3. For implementations adhering (only) to this
specification, they MUST be set as shown when sending and MUST be
ignored when receiving. This is to ensure optimal forward
compatibility. Note that for implementations that implement other
compatible specifications in addition to this specification, the
corresponding rules may well be different. For example, an
implementation that implements both this specification and the SHIM6
protocol may need to check these bits in order to determine how to
handle the packet.
The HIT fields are always 128 bits (16 bytes) long.
Moskowitz, et al. Standards Track [Page 39]
RFC 7401 HIPv2 April 2015
Since the checksum covers the source and destination addresses in the
IP header, it MUST be recomputed on HIP-aware NAT devices.
If IPv6 is used to carry the HIP packet, the pseudo header [RFC2460]
contains the source and destination IPv6 addresses, HIP packet length
in the pseudo header Length field, a zero field, and the HIP protocol
number (see Section 5.1) in the Next Header field. The Length field
is in bytes and can be calculated from the HIP Header Length field:
(HIP Header Length + 1) * 8.
In case of using IPv4, the IPv4 UDP pseudo header format [RFC0768] is
used. In the pseudo header, the source and destination addresses are
those used in the IP header, the zero field is obviously zero, the
protocol is the HIP protocol number (see Section 4), and the length
is calculated as in the IPv6 case.
5.1.2. HIP Controls
The HIP Controls field conveys information about the structure of the
packet and capabilities of the host.
The following fields have been defined:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | | | | | | | | | | | | | |A|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
A - Anonymous: If this is set, the sender's HI in this packet is
anonymous, i.e., one not listed in a directory. Anonymous HIs
SHOULD NOT be stored. This control is set in packets using
anonymous sender HIs. The peer receiving an anonymous HI in an R1
or I2 may choose to refuse it.
The rest of the fields are reserved for future use, and MUST be set
to zero in sent packets and MUST be ignored in received packets.
5.1.3. HIP Fragmentation Support
A HIP implementation MUST support IP fragmentation/reassembly.
Fragment reassembly MUST be implemented in both IPv4 and IPv6, but
fragment generation is REQUIRED to be implemented in IPv4 (IPv4
stacks and networks will usually do this by default) and RECOMMENDED
to be implemented in IPv6. In IPv6 networks, the minimum MTU is
larger, 1280 bytes, than in IPv4 networks. The larger MTU size is
usually sufficient for most HIP packets, and therefore fragment
Moskowitz, et al. Standards Track [Page 40]
RFC 7401 HIPv2 April 2015
generation may not be needed. If it is expected that a host will
send HIP packets that are larger than the minimum IPv6 MTU, the
implementation MUST implement fragment generation even for IPv6.
In IPv4 networks, HIP packets may encounter low MTUs along their
routed path. Since basic HIP, as defined in this document, does not
provide a mechanism to use multiple IP datagrams for a single HIP
packet, support for path MTU discovery does not bring any value to
HIP in IPv4 networks. HIP-aware NAT devices SHOULD perform IPv4
reassembly/fragmentation for HIP packets.
All HIP implementations have to be careful while employing a
reassembly algorithm so that the algorithm is sufficiently resistant
to DoS attacks.
Certificate chains can cause the packet to be fragmented, and
fragmentation can open implementations to denial-of-service attacks
[KAU03]. "Hash and URL" schemes as defined in [RFC6253] for HIP
version 1 may be used to avoid fragmentation and mitigate resulting
DoS attacks.
5.2. HIP Parameters
The HIP parameters carry information that is necessary for
establishing and maintaining a HIP association. For example, the
peer's public keys as well as the signaling for negotiating ciphers
and payload handling are encapsulated in HIP parameters. Additional
information, meaningful for end hosts or middleboxes, may also be
included in HIP parameters. The specification of the HIP parameters
and their mapping to HIP packets and packet types is flexible to
allow HIP extensions to define new parameters and new protocol
behavior.
In HIP packets, HIP parameters are ordered according to their numeric
type number and encoded in TLV format.
Moskowitz, et al. Standards Track [Page 41]
RFC 7401 HIPv2 April 2015
The following parameter types are currently defined.
+------------------------+-------+-----------+----------------------+
| TLV | Type | Length | Data |
+------------------------+-------+-----------+----------------------+
| R1_COUNTER | 129 | 12 | Puzzle generation |
| | | | counter |
| | | | |
| PUZZLE | 257 | 12 | #K and Random #I |
| | | | |
| SOLUTION | 321 | 20 | #K, Random #I and |
| | | | puzzle solution #J |
| | | | |
| SEQ | 385 | 4 | UPDATE packet ID |
| | | | number |
| | | | |
| ACK | 449 | variable | UPDATE packet ID |
| | | | number |
| | | | |
| DH_GROUP_LIST | 511 | variable | Ordered list of DH |
| | | | Group IDs supported |
| | | | by a host |
| | | | |
| DIFFIE_HELLMAN | 513 | variable | public key |
| | | | |
| HIP_CIPHER | 579 | variable | List of HIP |
| | | | encryption |
| | | | algorithms |
| | | | |
| ENCRYPTED | 641 | variable | Encrypted part of a |
| | | | HIP packet |
| | | | |
| HOST_ID | 705 | variable | Host Identity with |
| | | | Fully Qualified |
| | | | Domain Name (FQDN) |
| | | | or Network Access |
| | | | Identifier (NAI) |
| | | | |
| HIT_SUITE_LIST | 715 | variable | Ordered list of the |
| | | | HIT Suites supported |
| | | | by the Responder |
| | | | |
| CERT | 768 | variable | HI Certificate; used |
| | | | to transfer |
| | | | certificates. |
| | | | Specified in a |
| | | | separate document. |
| | | | |
Moskowitz, et al. Standards Track [Page 42]
RFC 7401 HIPv2 April 2015
| NOTIFICATION | 832 | variable | Informational data |
| | | | |
| ECHO_REQUEST_SIGNED | 897 | variable | Opaque data to be |
| | | | echoed back; signed |
| | | | |
| ECHO_RESPONSE_SIGNED | 961 | variable | Opaque data echoed |
| | | | back by request; |
| | | | signed |
| | | | |
| TRANSPORT_FORMAT_LIST | 2049 | Ordered | variable |
| | | list of | |
| | | preferred | |
| | | HIP | |
| | | transport | |
| | | type | |
| | | numbers | |
| | | | |
| HIP_MAC | 61505 | variable | HMAC-based message |
| | | | authentication code, |
| | | | with key material |
| | | | from KEYMAT |
| | | | |
| HIP_MAC_2 | 61569 | variable | HMAC-based message |
| | | | authentication code, |
| | | | with key material |
| | | | from KEYMAT. Unlike |
| | | | HIP_MAC, the HOST_ID |
| | | | parameter is |
| | | | included in |
| | | | HIP_MAC_2 |
| | | | calculation. |
| | | | |
| HIP_SIGNATURE_2 | 61633 | variable | Signature used in R1 |
| | | | packet |
| | | | |
| HIP_SIGNATURE | 61697 | variable | Signature of the |
| | | | packet |
| | | | |
| ECHO_REQUEST_UNSIGNED | 63661 | variable | Opaque data to be |
| | | | echoed back; after |
| | | | signature |
| | | | |
| ECHO_RESPONSE_UNSIGNED | 63425 | variable | Opaque data echoed |
| | | | back by request; |
| | | | after signature |
+------------------------+-------+-----------+----------------------+
Moskowitz, et al. Standards Track [Page 43]
RFC 7401 HIPv2 April 2015
As the ordering (from lowest to highest) of HIP parameters is
strictly enforced (see Section 5.2.1), the parameter type values for
existing parameters have been spaced to allow for future protocol
extensions.
The following parameter type number ranges are defined.
+---------------+---------------------------------------------------+
| Type Range | Purpose |
+---------------+---------------------------------------------------+
| 0 - 1023 | Handshake |
| | |
| 1024 - 2047 | Reserved |
| | |
| 2048 - 4095 | Parameters related to HIP transport formats |
| | |
| 4096 - 8191 | Signed parameters allocated through specification |
| | documents |
| | |
| 8192 - 32767 | Reserved |
| | |
| 32768 - 49151 | Reserved for Private Use. Signed parameters. |
| | |
| 49152 - 61439 | Reserved |
| | |
| 61440 - 62463 | Signatures and (signed) MACs |
| | |
| 62464 - 63487 | Parameters that are neither signed nor MACed |
| | |
| 63488 - 64511 | Rendezvous and relaying |
| | |
| 64512 - 65023 | Parameters that are neither signed nor MACed |
| | |
| 65024 - 65535 | Reserved |
+---------------+---------------------------------------------------+
The process for defining new parameters is described in Section 5.2.2
of this document.
The range between 32768 (2^15) and 49151 (2^15 + 2^14) is Reserved
for Private Use. Types from this range SHOULD be selected in a
random fashion to reduce the probability of collisions.
5.2.1. TLV Format
The TLV-encoded parameters are described in the following
subsections. The Type field value also describes the order of these
fields in the packet. The parameters MUST be included in the packet
Moskowitz, et al. Standards Track [Page 44]
RFC 7401 HIPv2 April 2015
so that their types form an increasing order. If multiple parameters
with the same type number are in one packet, the parameters with the
same type MUST be consecutive in the packet. If the order does not
follow this rule, the packet is considered to be malformed and it
MUST be discarded.
Parameters using type values from 2048 up to 4095 are related to
transport formats. Currently, one transport format is defined: the
ESP transport format [RFC7402].
All of the encoded TLV parameters have a length (that includes the
Type and Length fields), which is a multiple of 8 bytes. When
needed, padding MUST be added to the end of the parameter so that the
total length is a multiple of 8 bytes. This rule ensures proper
alignment of data. Any added padding bytes MUST be zeroed by the
sender, and their values SHOULD NOT be checked by the receiver.
The Length field indicates the length of the Contents field (in
bytes). Consequently, the total length of the TLV parameter
(including Type, Length, Contents, and Padding) is related to the
Length field according to the following formula:
Total Length = 11 + Length - (Length + 3) % 8;
where % is the modulo operator.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type |C| Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
/ Contents /
/ +-+-+-+-+-+-+-+-+
| | Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type Type code for the parameter. 16 bits long, C-bit
being part of the Type code.
C Critical. One if this parameter is critical and
MUST be recognized by the recipient, zero otherwise.
The C-bit is considered to be a part of the Type
field. Consequently, critical parameters are always
odd, and non-critical ones have an even value.
Length Length of the Contents, in bytes, excluding Type,
Length, and Padding
Contents Parameter specific, defined by Type
Padding Padding, 0-7 bytes, added if needed
Moskowitz, et al. Standards Track [Page 45]
RFC 7401 HIPv2 April 2015
Critical parameters (indicated by the odd type number value) MUST be
recognized by the recipient. If a recipient encounters a critical
parameter that it does not recognize, it MUST NOT process the packet
any further. It MAY send an ICMP or NOTIFY, as defined in
Section 4.3.
Non-critical parameters MAY be safely ignored. If a recipient
encounters a non-critical parameter that it does not recognize, it
SHOULD proceed as if the parameter was not present in the received
packet.
5.2.2. Defining New Parameters
Future specifications may define new parameters as needed. When
defining new parameters, care must be taken to ensure that the
parameter type values are appropriate and leave suitable space for
other future extensions. One must remember that the parameters MUST
always be arranged in numerically increasing order by Type code,
thereby limiting the order of parameters (see Section 5.2.1).
The following rules MUST be followed when defining new parameters.
1. The low-order bit C of the Type code is used to distinguish
between critical and non-critical parameters. Hence, even
parameter type numbers indicate non-critical parameters while odd
parameter type numbers indicate critical parameters.
2. A new parameter MAY be critical only if an old implementation
that ignored it would cause security problems. In general, new
parameters SHOULD be defined as non-critical, and expect a reply
from the recipient.
3. If a system implements a new critical parameter, it MUST provide
the ability to set the associated feature off, such that the
critical parameter is not sent at all. The configuration option
MUST be well documented. Implementations operating in a mode
adhering to this specification MUST disable the sending of new
critical parameters by default. In other words, the management
interface MUST allow vanilla standards-only mode as a default
configuration setting, and MAY allow new critical payloads to be
configured on (and off).
4. See Section 9 for allocation rules regarding Type codes.
Moskowitz, et al. Standards Track [Page 46]
RFC 7401 HIPv2 April 2015
5.2.3. R1_COUNTER
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved, 4 bytes |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| R1 generation counter, 8 bytes |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type 129
Length 12
R1 generation
counter The current generation of valid puzzles
The R1_COUNTER parameter contains a 64-bit unsigned integer in
network byte order, indicating the current generation of valid
puzzles. The sender SHOULD increment this counter periodically. It
is RECOMMENDED that the counter value is incremented at least as
often as old PUZZLE values are deprecated so that SOLUTIONs to them
are no longer accepted.
Support for the R1_COUNTER parameter is mandatory, although its
inclusion in the R1 packet is optional. It SHOULD be included in the
R1 (in which case it is covered by the signature), and if present in
the R1, it MUST be echoed (including the Reserved field verbatim) by
the Initiator in the I2 packet.
Moskowitz, et al. Standards Track [Page 47]
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| #K, 1 byte | Lifetime | Opaque, 2 bytes |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Random #I, RHASH_len / 8 bytes |
/ /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type 257
Length 4 + RHASH_len / 8
#K #K is the number of verified bits
Lifetime puzzle lifetime 2^(value - 32) seconds
Opaque data set by the Responder, indexing the puzzle
Random #I random number of size RHASH_len bits
Random #I is represented as an n-bit integer (where n is RHASH_len),
and #K and Lifetime as 8-bit integers, all in network byte order.
The PUZZLE parameter contains the puzzle difficulty #K and an n-bit
random integer #I. The Puzzle Lifetime indicates the time during
which the puzzle solution is valid, and sets a time limit that should
not be exceeded by the Initiator while it attempts to solve the
puzzle. The lifetime is indicated as a power of 2 using the formula
2^(Lifetime - 32) seconds. A puzzle MAY be augmented with an
ECHO_REQUEST_SIGNED or an ECHO_REQUEST_UNSIGNED parameter included in
the R1; the contents of the echo request are then echoed back in the
ECHO_RESPONSE_SIGNED or in the ECHO_RESPONSE_UNSIGNED parameter,
allowing the Responder to use the included information as a part of
its puzzle processing.
The Opaque and Random #I fields are not covered by the
HIP_SIGNATURE_2 parameter.
Moskowitz, et al. Standards Track [Page 48]
RFC 7401 HIPv2 April 2015
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| #K, 1 byte | Reserved | Opaque, 2 bytes |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Random #I, n bytes |
/ /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Puzzle solution #J, RHASH_len / 8 bytes |
/ /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type 321
Length 4 + RHASH_len / 4
#K #K is the number of verified bits
Reserved zero when sent, ignored when received
Opaque copied unmodified from the received PUZZLE
parameter
Random #I random number of size RHASH_len bits
Puzzle solution #J random number of size RHASH_len bits
Random #I and Random #J are represented as n-bit unsigned integers
(where n is RHASH_len), and #K as an 8-bit unsigned integer, all in
network byte order.
The SOLUTION parameter contains a solution to a puzzle. It also
echoes back the random difficulty #K, the Opaque field, and the
puzzle integer #I.
Moskowitz, et al. Standards Track [Page 49]
RFC 7401 HIPv2 April 2015
5.2.6. DH_GROUP_LIST
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| DH GROUP ID #1| DH GROUP ID #2| DH GROUP ID #3| DH GROUP ID #4|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| DH GROUP ID #n| Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type 511
Length number of DH Group IDs
DH GROUP ID identifies a DH GROUP ID supported by the host.
The list of IDs is ordered by preference of the
host. The possible DH Group IDs are defined
in the DIFFIE_HELLMAN parameter. Each DH
Group ID is one octet long.
The DH_GROUP_LIST parameter contains the list of supported DH Group
IDs of a host. The Initiator sends the DH_GROUP_LIST in the I1
packet, and the Responder sends its own list in the signed part of
the R1 packet. The DH Group IDs in the DH_GROUP_LIST are listed in
the order of their preference of the host sending the list. DH Group
IDs that are listed first are preferred over the DH Group IDs listed
later. The information in the DH_GROUP_LIST allows the Responder to
select the DH group preferred by itself and supported by the
Initiator. Based on the DH_GROUP_LIST in the R1 packet, the
Initiator can determine if the Responder has selected the best
possible choice based on the Initiator's and Responder's preferences.
If the Responder's choice differs from the best choice, the Initiator
can conclude that there was an attempted downgrade attack (see
Section 4.1.7).
When selecting the DH group for the DIFFIE_HELLMAN parameter in the
R1 packet, the Responder MUST select the first DH Group ID in its
DH_GROUP_LIST in the R1 packet that is compatible with one of the
Suite IDs in the Initiator's DH_GROUP_LIST in the I1 packet. The
Responder MUST NOT select any other DH Group ID that is contained in
both lists, because then a downgrade attack cannot be detected.
In general, hosts SHOULD prefer stronger groups over weaker ones if
the computation overhead is not prohibitively high for the intended
application.
Moskowitz, et al. Standards Track [Page 50]
RFC 7401 HIPv2 April 2015
5.2.7. DIFFIE_HELLMAN
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Group ID | Public Value Length | Public Value /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ | Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type 513
Length length in octets, excluding Type, Length, and
Padding
Group ID identifies values for p and g as well as the KDF
Public Value length of the following Public Value in octets
Length
Public Value the sender's public Diffie-Hellman key
A single DIFFIE_HELLMAN parameter may be included in selected HIP
packets based on the DH Group ID selected (Section 5.2.6). The
following Group IDs have been defined; values are assigned by this
document:
Group KDF Value
Reserved 0
DEPRECATED 1
DEPRECATED 2
1536-bit MODP group [RFC3526] HKDF [RFC5869] 3
3072-bit MODP group [RFC3526] HKDF [RFC5869] 4
DEPRECATED 5
DEPRECATED 6
NIST P-256 [RFC5903] HKDF [RFC5869] 7
NIST P-384 [RFC5903] HKDF [RFC5869] 8
NIST P-521 [RFC5903] HKDF [RFC5869] 9
SECP160R1 [SECG] HKDF [RFC5869] 10
2048-bit MODP group [RFC3526] HKDF [RFC5869] 11
The MODP Diffie-Hellman groups are defined in [RFC3526]. ECDH
groups 7-9 are defined in [RFC5903] and [RFC6090]. ECDH group 10
is covered in Appendix D. Any ECDH used with HIP MUST have a
co-factor of 1.
Moskowitz, et al. Standards Track [Page 51]
RFC 7401 HIPv2 April 2015
The Group ID also defines the key derivation function that is to be
used for deriving the symmetric keys for the HMAC and symmetric
encryption from the keying material from the Diffie-Hellman key
exchange (see Section 6.5).
A HIP implementation MUST implement Group ID 3. The 160-bit
SECP160R1 group can be used when lower security is enough (e.g., web
surfing) and when the equipment is not powerful enough (e.g., some
PDAs). Implementations SHOULD implement Group IDs 4 and 8.
To avoid unnecessary failures during the base exchange, the rest of
the groups SHOULD be implemented in hosts where resources are
adequate.
5.2.8. HIP_CIPHER
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Cipher ID #1 | Cipher ID #2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Cipher ID #n | Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type 579
Length length in octets, excluding Type, Length, and
Padding
Cipher ID identifies the cipher algorithm to be used for
encrypting the contents of the ENCRYPTED parameter
Moskowitz, et al. Standards Track [Page 52]
RFC 7401 HIPv2 April 2015
The following Cipher IDs are defined:
Suite ID Value
RESERVED 0
NULL-ENCRYPT 1 ([RFC2410])
AES-128-CBC 2 ([RFC3602])
RESERVED 3 (unused value)
AES-256-CBC 4 ([RFC3602])
The sender of a HIP_CIPHER parameter MUST make sure that there are no
more than six (6) Cipher IDs in one HIP_CIPHER parameter.
Conversely, a recipient MUST be prepared to handle received transport
parameters that contain more than six Cipher IDs by accepting the
first six Cipher IDs and dropping the rest. The limited number of
Cipher IDs sets the maximum size of the HIP_CIPHER parameter. As the
default configuration, the HIP_CIPHER parameter MUST contain at least
one of the mandatory Cipher IDs. There MAY be a configuration option
that allows the administrator to override this default.
The Responder lists supported and desired Cipher IDs in order of
preference in the R1, up to the maximum of six Cipher IDs. The
Initiator MUST choose only one of the corresponding Cipher IDs. This
Cipher ID will be used for generating the ENCRYPTED parameter.
Mandatory implementation: AES-128-CBC. Implementors SHOULD support
NULL-ENCRYPT for testing/debugging purposes but MUST NOT offer or
accept this value unless explicitly configured for testing/debugging
of HIP.
Moskowitz, et al. Standards Track [Page 53]
RFC 7401 HIPv2 April 2015
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| HI Length |DI-Type| DI Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Algorithm | Host Identity /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ | Domain Identifier /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ | Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type 705
Length length in octets, excluding Type, Length, and
Padding
HI Length length of the Host Identity in octets
DI-Type type of the following Domain Identifier field
DI Length length of the Domain Identifier field in octets
Algorithm index to the employed algorithm
Host Identity actual Host Identity
Domain Identifier the identifier of the sender
The following DI-Types have been defined:
Type Value
none included 0
FQDN 1
NAI 2
FQDN Fully Qualified Domain Name, in binary format
NAI Network Access Identifier
The format for the FQDN is defined in RFC 1035 [RFC1035],
Section 3.1. The format for the NAI is defined in [RFC4282].
A host MAY optionally associate the Host Identity with a single
Domain Identifier in the HOST_ID parameter. If there is no Domain
Identifier, i.e., the DI-Type field is zero, the DI Length field is
set to zero as well.
Moskowitz, et al. Standards Track [Page 54]
RFC 7401 HIPv2 April 2015
The following HI Algorithms have been defined:
Algorithm profiles Values
RESERVED 0
DSA 3 [FIPS.186-4.2013] (RECOMMENDED)
RSA 5 [RFC3447] (REQUIRED)
ECDSA 7 [RFC4754] (REQUIRED)
ECDSA_LOW 9 [SECG] (RECOMMENDED)
For DSA, RSA, and ECDSA key types, profiles containing at least
112 bits of security strength (as defined by [NIST.800-131A.2011])
should be used. For RSA signature padding, the Probabilistic
Signature Scheme (PSS) method of padding [RFC3447] MUST be used.
The Host Identity is derived from the DNSKEY format for RSA and DSA.
For these, the Public Key field of the RDATA part from RFC 4034
[RFC4034] is used. For Elliptic Curve Cryptography (ECC), we
distinguish two different profiles: ECDSA and ECDSA_LOW. ECC
contains curves approved by NIST and defined in RFC 4754 [RFC4754].
ECDSA_LOW is defined for devices with low computational capabilities
and uses shorter curves from the Standards for Efficient Cryptography
Group [SECG]. Any ECDSA used with HIP MUST have a co-factor of 1.
For ECDSA and ECDSA_LOW, Host Identities are represented by the
following fields:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ECC Curve | /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ Public Key |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
ECC Curve Curve label
Public Key Represented in octet-string format [RFC6090]
For hosts that implement ECDSA as the algorithm, the following ECC
curves are required:
Algorithm Curve Values
ECDSA RESERVED 0
ECDSA NIST P-256 1 [RFC4754]
ECDSA NIST P-384 2 [RFC4754]
Moskowitz, et al. Standards Track [Page 55]
RFC 7401 HIPv2 April 2015
For hosts that implement the ECDSA_LOW algorithm profile, the
following curve is required:
Algorithm Curve Values
ECDSA_LOW RESERVED 0
ECDSA_LOW SECP160R1 1 [SECG]
5.2.10. HIT_SUITE_LIST
The HIT_SUITE_LIST parameter contains a list of the supported HIT
Suite IDs of the Responder. The Responder sends the HIT_SUITE_LIST
in the signed part of the R1 packet. Based on the HIT_SUITE_LIST,
the Initiator can determine which source HIT Suite IDs are supported
by the Responder.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ID #1 | ID #2 | ID #3 | ID #4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ID #n | Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type 715
Length number of HIT Suite IDs
ID identifies a HIT Suite ID supported by the host.
The list of IDs is ordered by preference of the
host. Each HIT Suite ID is one octet long. The
four higher-order bits of the ID field correspond
to the HIT Suite ID in the ORCHID OGA ID field. The
four lower-order bits are reserved and set to 0
by the sender. The reception of an ID with the
four lower-order bits not set to 0 SHOULD be
considered as an error that MAY result in a
NOTIFICATION of type UNSUPPORTED_HIT_SUITE.
The HIT Suite ID indexes a HIT Suite. HIT Suites are composed of
signature algorithms as defined in Section 5.2.9, and hash functions.
The ID field in the HIT_SUITE_LIST is defined as an eight-bit field,
as opposed to the four-bit HIT Suite ID and OGA ID field in the
ORCHID. This difference is a measure to accommodate larger HIT Suite
IDs if the 16 available values prove insufficient. In that case, one
of the 16 values, zero, will be used to indicate that four additional
bits of the ORCHID will be used to encode the HIT Suite ID. Hence,
Moskowitz, et al. Standards Track [Page 56]
RFC 7401 HIPv2 April 2015
the current four-bit HIT Suite IDs only use the four higher-order
bits in the ID field. Future documents may define the use of the
four lower-order bits in the ID field.
The following HIT Suite IDs are defined, and the relationship between
the four-bit ID value used in the OGA ID field and the eight-bit
encoding within the HIT_SUITE_LIST ID field is clarified:
HIT Suite Four-bit ID Eight-bit encoding
RESERVED 0 0x00
RSA,DSA/SHA-256 1 0x10 (REQUIRED)
ECDSA/SHA-384 2 0x20 (RECOMMENDED)
ECDSA_LOW/SHA-1 3 0x30 (RECOMMENDED)
The following table provides more detail on the above HIT Suite
combinations. The input for each generation algorithm is the
encoding of the HI as defined in Section 3.2. The output is 96 bits
long and is directly used in the ORCHID.
+-------+----------+--------------+------------+--------------------+
| Index | Hash | HMAC | Signature | Description |
| | function | | algorithm | |
| | | | family | |
+-------+----------+--------------+------------+--------------------+
| 0 | | | | Reserved |
| | | | | |
| 1 | SHA-256 | HMAC-SHA-256 | RSA, DSA | RSA or DSA HI |
| | | | | hashed with |
| | | | | SHA-256, truncated |
| | | | | to 96 bits |
| | | | | |
| 2 | SHA-384 | HMAC-SHA-384 | ECDSA | ECDSA HI hashed |
| | | | | with SHA-384, |
| | | | | truncated to 96 |
| | | | | bits |
| | | | | |
| 3 | SHA-1 | HMAC-SHA-1 | ECDSA_LOW | ECDSA_LOW HI |
| | | | | hashed with SHA-1, |
| | | | | truncated to 96 |
| | | | | bits |
+-------+----------+--------------+------------+--------------------+
Table 10: HIT Suites
Moskowitz, et al. Standards Track [Page 57]
RFC 7401 HIPv2 April 2015
The hash of the Responder as defined in the HIT Suite determines the
HMAC to be used for the RHASH function. The HMACs currently defined
here are HMAC-SHA-256 [RFC4868], HMAC-SHA-384 [RFC4868], and
HMAC-SHA-1 [RFC2404].
5.2.11. TRANSPORT_FORMAT_LIST
The TRANSPORT_FORMAT_LIST parameter contains a list of the supported
HIP transport formats (TFs) of the Responder. The Responder sends
the TRANSPORT_FORMAT_LIST in the signed part of the R1 packet. Based
on the TRANSPORT_FORMAT_LIST, the Initiator chooses one suitable
transport format and includes the respective HIP transport format
parameter in its response packet.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TF type #1 | TF type #2 /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ TF type #n | Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type 2049
Length 2x number of TF types
TF Type identifies a transport format (TF) type supported
by the host. The TF type numbers correspond to
the HIP parameter type numbers of the respective
transport format parameters. The list of TF types
is ordered by preference of the sender.
The TF type numbers index the respective HIP parameters for the
transport formats in the type number range between 2050 and 4095.
The parameters and their use are defined in separate documents.
Currently, the only transport format defined is IPsec ESP [RFC7402].
For each listed TF type, the sender of the TRANSPORT_FORMAT_LIST
parameter MUST include the respective transport format parameter in
the HIP packet. The receiver MUST ignore the TF type in the
TRANSPORT_FORMAT_LIST if no matching transport format parameter is
present in the packet.
Moskowitz, et al. Standards Track [Page 58]
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| HMAC |
/ /
/ +-------------------------------+
| | Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type 61505
Length length in octets, excluding Type, Length, and
Padding
HMAC HMAC computed over the HIP packet, excluding the
HIP_MAC parameter and any following parameters,
such as HIP_SIGNATURE, HIP_SIGNATURE_2,
ECHO_REQUEST_UNSIGNED, or ECHO_RESPONSE_UNSIGNED.
The Checksum field MUST be set to zero, and the
HIP header length in the HIP common header MUST be
calculated not to cover any excluded parameters
when the HMAC is calculated. The size of the
HMAC is the natural size of the hash computation
output depending on the used hash function.
The HMAC uses RHASH as the hash algorithm. The calculation and
verification process is presented in Section 6.4.1.
HIP_MAC_2 is a MAC of the packet and the HI of the sender in the form
of a HOST_ID parameter when that parameter is not actually included
in the packet. The parameter structure is the same as the structure
shown in Section 5.2.12. The fields are as follows:
Type 61569
Length length in octets, excluding Type, Length, and
Padding
HMAC HMAC computed over the HIP packet, excluding the
HIP_MAC_2 parameter and any following parameters
such as HIP_SIGNATURE, HIP_SIGNATURE_2,
ECHO_REQUEST_UNSIGNED, or ECHO_RESPONSE_UNSIGNED,
and including an additional sender's HOST_ID
parameter during the HMAC calculation. The
Checksum field MUST be set to zero, and the HIP
Moskowitz, et al. Standards Track [Page 59]
RFC 7401 HIPv2 April 2015
header length in the HIP common header MUST be
calculated not to cover any excluded parameters
when the HMAC is calculated. The size of the
HMAC is the natural size of the hash computation
output depending on the used hash function.
The HMAC uses RHASH as the hash algorithm. The calculation and
verification process is presented in Section 6.4.1.
5.2.14. HIP_SIGNATURE
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SIG alg | Signature /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ | Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type 61697
Length length in octets, excluding Type, Length, and
Padding
SIG alg signature algorithm
Signature the signature is calculated over the HIP packet,
excluding the HIP_SIGNATURE parameter and any
parameters that follow the HIP_SIGNATURE
parameter. When the signature is calculated, the
Checksum field MUST be set to zero, and the HIP
header length in the HIP common header MUST be
calculated only up to the beginning of the
HIP_SIGNATURE parameter.
The signature algorithms are defined in Section 5.2.9. The signature
in the Signature field is encoded using the method depending on the
signature algorithm (e.g., according to [RFC3110] in the case of RSA/
SHA-1, [RFC5702] in the case of RSA/SHA-256, [RFC2536] in the case of
DSA, or [RFC6090] in the case of ECDSA).
HIP_SIGNATURE calculation and verification follow the process defined
in Section 6.4.2.
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5.2.15. HIP_SIGNATURE_2
HIP_SIGNATURE_2 excludes the variable parameters in the R1 packet to
allow R1 pre-creation. The parameter structure is the same as the
structure shown in Section 5.2.14. The fields are as follows:
Type 61633
Length length in octets, excluding Type, Length, and
Padding
SIG alg signature algorithm
Signature Within the R1 packet that contains the
HIP_SIGNATURE_2 parameter, the Initiator's HIT, the
Checksum field, and the Opaque and Random #I fields
in the PUZZLE parameter MUST be set to zero while
computing the HIP_SIGNATURE_2 signature. Further,
the HIP packet length in the HIP header MUST be
adjusted as if the HIP_SIGNATURE_2 was not in the
packet during the signature calculation, i.e., the
HIP packet length points to the beginning of
the HIP_SIGNATURE_2 parameter during signing and
verification.
Zeroing the Initiator's HIT makes it possible to create R1 packets
beforehand, to minimize the effects of possible DoS attacks. Zeroing
the Random #I and Opaque fields within the PUZZLE parameter allows
these fields to be populated dynamically on precomputed R1s.
Signature calculation and verification follow the process defined in
Section 6.4.2.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Update ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type 385
Length 4
Update ID 32-bit sequence number
The Update ID is an unsigned number in network byte order,
initialized by a host to zero upon moving to ESTABLISHED state. The
Update ID has scope within a single HIP association, and not across
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multiple associations or multiple hosts. The Update ID is
incremented by one before each new UPDATE that is sent by the host;
the first UPDATE packet originated by a host has an Update ID of 0.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| peer Update ID 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ peer Update ID n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type 449
Length length in octets, excluding Type and Length
peer Update ID 32-bit sequence number corresponding to the
Update ID being ACKed
The ACK parameter includes one or more Update IDs that have been
received from the peer. The number of peer Update IDs can be
inferred from the length by dividing it by 4.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IV /
/ /
/ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ /
/ Encrypted data /
/ /
/ +-------------------------------+
/ | Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type 641
Length length in octets, excluding Type, Length, and
Padding
Reserved zero when sent, ignored when received
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IV Initialization vector, if needed, otherwise
nonexistent. The length of the IV is inferred from
the HIP_CIPHER.
Encrypted The data is encrypted using the encryption algorithm
data defined in the HIP_CIPHER parameter.
The ENCRYPTED parameter encapsulates other parameters, the encrypted
data, which holds one or more HIP parameters in block encrypted form.
Consequently, the first fields in the encapsulated parameter(s) are
Type and Length of the first such parameter, allowing the contents to
be easily parsed after decryption.
The field labeled "Encrypted data" consists of the output of one or
more HIP parameters concatenated together that have been passed
through an encryption algorithm. Each of these inner parameters is
padded according to the rules of Section 5.2.1 for padding individual
parameters. As a result, the concatenated parameters will be a block
of data that is 8-byte aligned.
Some encryption algorithms require that the data to be encrypted must
be a multiple of the cipher algorithm block size. In this case, the
above block of data MUST include additional padding, as specified by
the encryption algorithm. The size of the extra padding is selected
so that the length of the unencrypted data block is a multiple of the
cipher block size. The encryption algorithm may specify padding
bytes other than zero; for example, AES [FIPS.197.2001] uses the
PKCS5 padding scheme (see Section 6.1.1 of [RFC2898]) where the
remaining n bytes to fill the block each have the value of n. This
yields an "unencrypted data" block that is transformed to an
"encrypted data" block by the cipher suite. This extra padding added
to the set of parameters to satisfy the cipher block alignment rules
is not counted in HIP TLV Length fields, and this extra padding
should be removed by the cipher suite upon decryption.
Note that the length of the cipher suite output may be smaller or
larger than the length of the set of parameters to be encrypted,
since the encryption process may compress the data or add additional
padding to the data.
Once this encryption process is completed, the Encrypted data field
is ready for inclusion in the parameter. If necessary, additional
Padding for 8-byte alignment is then added according to the rules of
Section 5.2.1.
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5.2.19. NOTIFICATION
The NOTIFICATION parameter is used to transmit informational data,
such as error conditions and state transitions, to a HIP peer. A
NOTIFICATION parameter may appear in NOTIFY packets. The use of the
NOTIFICATION parameter in other packet types is for further study.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Notify Message Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| /
/ Notification Data /
/ +---------------+
/ | Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type 832
Length length in octets, excluding Type, Length, and
Padding
Reserved zero when sent, ignored when received
Notify Message specifies the type of notification
Type
Notification informational or error data transmitted in
Data addition to the Notify Message Type. Values
for this field are type specific (see below).
Notification information can be error messages specifying why a HIP
Security Association could not be established. It can also be status
data that a HIP implementation wishes to communicate with a peer
process. The table below lists the notification messages and their
Notify Message Types. HIP packets MAY contain multiple NOTIFICATION
parameters if several problems exist or several independent pieces of
information must be transmitted.
To avoid certain types of attacks, a Responder SHOULD avoid sending a
NOTIFICATION to any host with which it has not successfully verified
a puzzle solution.
Notify Message Types in the range 0-16383 are intended for reporting
errors, and those in the range 16384-65535 are for other status
information. An implementation that receives a NOTIFY packet with a
Notify Message Type that indicates an error in response to a request
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packet (e.g., I1, I2, UPDATE) SHOULD assume that the corresponding
request has failed entirely. Unrecognized error types MUST be
ignored, except that they SHOULD be logged.
As currently defined, Notify Message Type values 1-10 are used for
informing about errors in packet structures, and values 11-20 for
informing about problems in parameters.
Notification Data in NOTIFICATION parameters where the Notify Message
Type is in the status range MUST be ignored if not recognized.
Notify Message Types - Errors Value
----------------------------- -----
UNSUPPORTED_CRITICAL_PARAMETER_TYPE 1
Sent if the parameter type has the "critical" bit set and the
parameter type is not recognized. Notification Data contains the
two-octet parameter type.
INVALID_SYNTAX 7
Indicates that the HIP message received was invalid because some
type, length, or value was out of range or because the request
was otherwise malformed. To avoid a denial-of-service
attack using forged messages, this status may only be returned
for packets whose HIP_MAC (if present) and SIGNATURE have been
verified. This status MUST be sent in response to any error not
covered by one of the other status types and SHOULD NOT contain
details, to avoid leaking information to someone probing a node.
To aid debugging, more detailed error information SHOULD be
written to a console or log.
NO_DH_PROPOSAL_CHOSEN 14
None of the proposed Group IDs were acceptable.
INVALID_DH_CHOSEN 15
The DH Group ID field does not correspond to one offered
by the Responder.
NO_HIP_PROPOSAL_CHOSEN 16
None of the proposed HIT Suites or HIP Encryption Algorithms were
acceptable.
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INVALID_HIP_CIPHER_CHOSEN 17
The HIP_CIPHER Crypto ID does not correspond to one offered by
the Responder.
UNSUPPORTED_HIT_SUITE 20
Sent in response to an I1 or R1 packet for which the HIT Suite
is not supported.
AUTHENTICATION_FAILED 24
Sent in response to a HIP signature failure, except when
the signature verification fails in a NOTIFY message.
CHECKSUM_FAILED 26
Sent in response to a HIP checksum failure.
HIP_MAC_FAILED 28
Sent in response to a HIP HMAC failure.
ENCRYPTION_FAILED 32
The Responder could not successfully decrypt the
ENCRYPTED parameter.
INVALID_HIT 40
Sent in response to a failure to validate the peer's
HIT from the corresponding HI.
BLOCKED_BY_POLICY 42
The Responder is unwilling to set up an association
for some policy reason (e.g., the received HIT is NULL
and the policy does not allow opportunistic mode).
RESPONDER_BUSY_PLEASE_RETRY 44
The Responder is unwilling to set up an association, as it is
suffering under some kind of overload and has chosen to shed load
by rejecting the Initiator's request. The Initiator may retry;
however, the Initiator MUST find another (different) puzzle
solution for any such retries. Note that the Initiator may need
to obtain a new puzzle with a new I1/R1 exchange.
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Notify Message Types - Status Value
----------------------------- -----
I2_ACKNOWLEDGEMENT 16384
The Responder has an I2 packet from the Initiator but had to
queue the I2 packet for processing. The puzzle was correctly
solved, and the Responder is willing to set up an association but
currently has a number of I2 packets in the processing queue.
The R2 packet is sent after the I2 packet was processed.
5.2.20. ECHO_REQUEST_SIGNED
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opaque data (variable length) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type 897
Length length of the opaque data in octets
Opaque data opaque data, supposed to be meaningful only to
the node that sends ECHO_REQUEST_SIGNED and
receives a corresponding ECHO_RESPONSE_SIGNED or
ECHO_RESPONSE_UNSIGNED
The ECHO_REQUEST_SIGNED parameter contains an opaque blob of data
that the sender wants to get echoed back in the corresponding reply
packet.
The ECHO_REQUEST_SIGNED and corresponding echo response parameters
MAY be used for any purpose where a node wants to carry some state in
a request packet and get it back in a response packet. The
ECHO_REQUEST_SIGNED is covered by the HIP_MAC and SIGNATURE. A HIP
packet can contain only one ECHO_REQUEST_SIGNED parameter and MAY
contain multiple ECHO_REQUEST_UNSIGNED parameters. The
ECHO_REQUEST_SIGNED parameter MUST be responded to with an
ECHO_RESPONSE_SIGNED.
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5.2.21. ECHO_REQUEST_UNSIGNED
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opaque data (variable length) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type 63661
Length length of the opaque data in octets
Opaque data opaque data, supposed to be meaningful only to
the node that sends ECHO_REQUEST_UNSIGNED and
receives a corresponding ECHO_RESPONSE_UNSIGNED
The ECHO_REQUEST_UNSIGNED parameter contains an opaque blob of data
that the sender wants to get echoed back in the corresponding reply
packet.
The ECHO_REQUEST_UNSIGNED and corresponding echo response parameters
MAY be used for any purpose where a node wants to carry some state in
a request packet and get it back in a response packet. The
ECHO_REQUEST_UNSIGNED is not covered by the HIP_MAC and SIGNATURE. A
HIP packet can contain one or more ECHO_REQUEST_UNSIGNED parameters.
It is possible that middleboxes add ECHO_REQUEST_UNSIGNED parameters
in HIP packets passing by. The creator of the ECHO_REQUEST_UNSIGNED
(end host or middlebox) has to create the Opaque field so that it can
later identify and remove the corresponding ECHO_RESPONSE_UNSIGNED
parameter.
The ECHO_REQUEST_UNSIGNED parameter MUST be responded to with an
ECHO_RESPONSE_UNSIGNED parameter.
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5.2.22. ECHO_RESPONSE_SIGNED
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opaque data (variable length) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type 961
Length length of the opaque data in octets
Opaque data opaque data, copied unmodified from the
ECHO_REQUEST_SIGNED or ECHO_REQUEST_UNSIGNED
parameter that triggered this response
The ECHO_RESPONSE_SIGNED parameter contains an opaque blob of data
that the sender of the ECHO_REQUEST_SIGNED wants to get echoed back.
The opaque data is copied unmodified from the ECHO_REQUEST_SIGNED
parameter.
The ECHO_REQUEST_SIGNED and ECHO_RESPONSE_SIGNED parameters MAY be
used for any purpose where a node wants to carry some state in a
request packet and get it back in a response packet. The
ECHO_RESPONSE_SIGNED is covered by the HIP_MAC and SIGNATURE.
5.2.23. ECHO_RESPONSE_UNSIGNED
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opaque data (variable length) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type 63425
Length length of the opaque data in octets
Opaque data opaque data, copied unmodified from the
ECHO_REQUEST_SIGNED or ECHO_REQUEST_UNSIGNED
parameter that triggered this response
The ECHO_RESPONSE_UNSIGNED parameter contains an opaque blob of data
that the sender of the ECHO_REQUEST_SIGNED or ECHO_REQUEST_UNSIGNED
wants to get echoed back. The opaque data is copied unmodified from
the corresponding echo request parameter.
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The echo request and ECHO_RESPONSE_UNSIGNED parameters MAY be used
for any purpose where a node wants to carry some state in a request
packet and get it back in a response packet. The
ECHO_RESPONSE_UNSIGNED is not covered by the HIP_MAC and SIGNATURE.
5.3. HIP Packets
There are eight basic HIP packets (see Table 11). Four are for the
HIP base exchange, one is for updating, one is for sending
notifications, and two are for closing a HIP association. Support
for the NOTIFY packet type is optional, but support for all other HIP
packet types listed below is mandatory.
+------------------+------------------------------------------------+
| Packet type | Packet name |
+------------------+------------------------------------------------+
| 1 | I1 - the HIP Initiator Packet |
| | |
| 2 | R1 - the HIP Responder Packet |
| | |
| 3 | I2 - the Second HIP Initiator Packet |
| | |
| 4 | R2 - the Second HIP Responder Packet |
| | |
| 16 | UPDATE - the HIP Update Packet |
| | |
| 17 | NOTIFY - the HIP Notify Packet |
| | |
| 18 | CLOSE - the HIP Association Closing Packet |
| | |
| 19 | CLOSE_ACK - the HIP Closing Acknowledgment |
| | Packet |
+------------------+------------------------------------------------+
Table 11: HIP Packets and Packet Type Values
Packets consist of the fixed header as described in Section 5.1,
followed by the parameters. The parameter part, in turn, consists of
zero or more TLV-coded parameters.
In addition to the base packets, other packet types may be defined
later in separate specifications. For example, support for mobility
and multihoming is not included in this specification.
See "Notation" (Section 2.2) for the notation used in the operations.
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In the future, an optional upper-layer payload MAY follow the HIP
header. The Next Header field in the header indicates if there is
additional data following the HIP header. The HIP packet, however,
MUST NOT be fragmented into multiple extension headers by setting the
Next Header field in a HIP header to the HIP protocol number. This
limits the size of the possible additional data in the packet.
5.3.1. I1 - the HIP Initiator Packet
The HIP header values for the I1 packet:
Header:
Packet Type = 1
SRC HIT = Initiator's HIT
DST HIT = Responder's HIT, or NULL
IP ( HIP ( DH_GROUP_LIST ) )
The I1 packet contains the fixed HIP header and the Initiator's
DH_GROUP_LIST.
Valid control bits: None
The Initiator receives the Responder's HIT from either a DNS lookup
of the Responder's FQDN (see [HIP-DNS-EXT]), some other repository,
or a local table. If the Initiator does not know the Responder's
HIT, it may attempt to use opportunistic mode by using NULL (all
zeros) as the Responder's HIT. See also "HIP Opportunistic Mode"
(Section 4.1.8).
Since the I1 packet is so easy to spoof even if it were signed, no
attempt is made to add to its generation or processing cost.
The Initiator includes a DH_GROUP_LIST parameter in the I1 packet to
inform the Responder of its preferred DH Group IDs. Note that the
DH_GROUP_LIST in the I1 packet is not protected by a signature.
Implementations MUST be able to handle a storm of received I1
packets, discarding those with common content that arrive within a
small time delta.
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5.3.2. R1 - the HIP Responder Packet
The HIP header values for the R1 packet:
Header:
Packet Type = 2
SRC HIT = Responder's HIT
DST HIT = Initiator's HIT
IP ( HIP ( [ R1_COUNTER, ]
PUZZLE,
DIFFIE_HELLMAN,
HIP_CIPHER,
HOST_ID,
HIT_SUITE_LIST,
DH_GROUP_LIST,
[ ECHO_REQUEST_SIGNED, ]
TRANSPORT_FORMAT_LIST,
HIP_SIGNATURE_2 )
<, ECHO_REQUEST_UNSIGNED >i)
Valid control bits: A
If the Responder's HI is an anonymous one, the A control MUST be set.
The Initiator's HIT MUST match the one received in the I1 packet if
the R1 is a response to an I1. If the Responder has multiple HIs,
the Responder's HIT used MUST match the Initiator's request. If the
Initiator used opportunistic mode, the Responder may select freely
among its HIs. See also "HIP Opportunistic Mode" (Section 4.1.8).
The R1 packet generation counter is used to determine the currently
valid generation of puzzles. The value is increased periodically,
and it is RECOMMENDED that it is increased at least as often as
solutions to old puzzles are no longer accepted.
The puzzle contains a Random #I and the difficulty #K. The
difficulty #K indicates the number of lower-order bits, in the puzzle
hash result, that must be zeros; see Section 4.1.2. The Random #I is
not covered by the signature and must be zeroed during the signature
calculation, allowing the sender to select and set the #I into a
precomputed R1 packet just prior to sending it to the peer.
The Responder selects the DIFFIE_HELLMAN Group ID and Public Value
based on the Initiator's preference expressed in the DH_GROUP_LIST
parameter in the I1 packet. The Responder sends back its own
preference based on which it chose the DH public value as
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DH_GROUP_LIST. This allows the Initiator to determine whether its
own DH_GROUP_LIST in the sent I1 packet was manipulated by an
attacker.
The Diffie-Hellman public value is ephemeral, and values SHOULD NOT
be reused across different HIP associations. Once the Responder has
received a valid response to an R1 packet, that Diffie-Hellman value
SHOULD be deprecated. It is possible that the Responder has sent the
same Diffie-Hellman value to different hosts simultaneously in
corresponding R1 packets, and those responses should also be
accepted. However, as a defense against I1 packet storms, an
implementation MAY propose, and reuse unless avoidable, the same
Diffie-Hellman value for a period of time -- for example, 15 minutes.
By using a small number of different puzzles for a given
Diffie-Hellman value, the R1 packets can be precomputed and delivered
as quickly as I1 packets arrive. A scavenger process should clean up
unused Diffie-Hellman values and puzzles.
Reusing Diffie-Hellman public values opens up the potential security
risk of more than one Initiator ending up with the same keying
material (due to faulty random number generators). Also, more than
one Initiator using the same Responder public key half may lead to
potentially easier cryptographic attacks and to imperfect forward
security.
However, these risks involved in reusing the same public value are
statistical; that is, the authors are not aware of any mechanism that
would allow manipulation of the protocol so that the risk of the
reuse of any given Responder Diffie-Hellman public key would differ
from the base probability. Consequently, it is RECOMMENDED that
Responders avoid reusing the same DH key with multiple Initiators,
but because the risk is considered statistical and not known to be
manipulable, the implementations MAY reuse a key in order to ease
resource-constrained implementations and to increase the probability
of successful communication with legitimate clients even under an I1
packet storm. In particular, when it is too expensive to generate
enough precomputed R1 packets to supply each potential Initiator with
a different DH key, the Responder MAY send the same DH key to several
Initiators, thereby creating the possibility of multiple legitimate
Initiators ending up using the same Responder-side public key.
However, as soon as the Responder knows that it will use a particular
DH key, it SHOULD stop offering it. This design is aimed to allow
resource-constrained Responders to offer services under I1 packet
storms and to simultaneously make the probability of DH key reuse
both statistical and as low as possible.
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If the Responder uses the same DH key pair for multiple handshakes,
it must take care to avoid small subgroup attacks [RFC2785]. To
avoid these attacks, when receiving the I2 message, the Responder
SHOULD validate the Initiator's DH public key as described in
[RFC2785], Section 3.1. If the validation fails, the Responder MUST
NOT generate a DH shared key and MUST silently abort the HIP BEX.
The HIP_CIPHER parameter contains the encryption algorithms supported
by the Responder to encrypt the contents of the ENCRYPTED parameter,
in the order of preference. All implementations MUST support AES
[RFC3602].
The HIT_SUITE_LIST parameter is an ordered list of the Responder's
preferred and supported HIT Suites. The list allows the Initiator to
determine whether its own source HIT matches any suite supported by
the Responder.
The ECHO_REQUEST_SIGNED and ECHO_REQUEST_UNSIGNED parameters contain
data that the sender wants to receive unmodified in the corresponding
response packet in the ECHO_RESPONSE_SIGNED or ECHO_RESPONSE_UNSIGNED
parameter. The R1 packet may contain zero or more
ECHO_REQUEST_UNSIGNED parameters as described in Section 5.2.21.
The TRANSPORT_FORMAT_LIST parameter is an ordered list of the
Responder's preferred and supported transport format types. The list
allows the Initiator and the Responder to agree on a common type for
payload protection. This parameter is described in Section 5.2.11.
The signature is calculated over the whole HIP packet as described in
Section 5.2.15. This allows the Responder to use precomputed R1s.
The Initiator SHOULD validate this signature. It MUST check that the
Responder's HI matches with the one expected, if any.
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5.3.3. I2 - the Second HIP Initiator Packet
The HIP header values for the I2 packet:
Header:
Packet Type = 3
SRC HIT = Initiator's HIT
DST HIT = Responder's HIT
IP ( HIP ( [R1_COUNTER,]
SOLUTION,
DIFFIE_HELLMAN,
HIP_CIPHER,
ENCRYPTED { HOST_ID } or HOST_ID,
[ ECHO_RESPONSE_SIGNED, ]
TRANSPORT_FORMAT_LIST,
HIP_MAC,
HIP_SIGNATURE
<, ECHO_RESPONSE_UNSIGNED>i ) )
Valid control bits: A
The HITs used MUST match the ones used in the R1.
If the Initiator's HI is an anonymous one, the A control bit MUST
be set.
If present in the I1 packet, the Initiator MUST include an unmodified
copy of the R1_COUNTER parameter received in the corresponding R1
packet into the I2 packet.
The Solution contains the Random #I from R1 and the computed #J. The
low-order #K bits of the RHASH( #I | ... | #J ) MUST be zero.
The Diffie-Hellman value is ephemeral. If precomputed, a scavenger
process should clean up unused Diffie-Hellman values. The Responder
MAY reuse Diffie-Hellman values under some conditions as specified in
Section 5.3.2.
The HIP_CIPHER contains the single encryption suite selected by the
Initiator, that it uses to encrypt the ENCRYPTED parameters. The
chosen cipher MUST correspond to one of the ciphers offered by the
Responder in the R1. All implementations MUST support AES [RFC3602].
The Initiator's HI MAY be encrypted using the HIP_CIPHER encryption
algorithm. The keying material is derived from the Diffie-Hellman
exchange as defined in Section 6.5.
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The ECHO_RESPONSE_SIGNED and ECHO_RESPONSE_UNSIGNED contain the
unmodified opaque data copied from the corresponding echo request
parameter(s).
The TRANSPORT_FORMAT_LIST contains the single transport format type
selected by the Initiator. The chosen type MUST correspond to one of
the types offered by the Responder in the R1. Currently, the only
transport format defined is the ESP transport format ([RFC7402]).
The HMAC value in the HIP_MAC parameter is calculated over the whole
HIP packet, excluding any parameters after the HIP_MAC, as described
in Section 6.4.1. The Responder MUST validate the HIP_MAC.
The signature is calculated over the whole HIP packet, excluding any
parameters after the HIP_SIGNATURE, as described in Section 5.2.14.
The Responder MUST validate this signature. The Responder uses the
HI in the packet or an HI acquired by some other means for verifying
the signature.
5.3.4. R2 - the Second HIP Responder Packet
The HIP header values for the R2 packet:
Header:
Packet Type = 4
SRC HIT = Responder's HIT
DST HIT = Initiator's HIT
IP ( HIP ( HIP_MAC_2, HIP_SIGNATURE ) )
Valid control bits: None
The HIP_MAC_2 is calculated over the whole HIP packet, with the
Responder's HOST_ID parameter concatenated with the HIP packet. The
HOST_ID parameter is removed after the HMAC calculation. The
procedure is described in Section 6.4.1.
The signature is calculated over the whole HIP packet.
The Initiator MUST validate both the HIP_MAC and the signature.
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5.3.5. UPDATE - the HIP Update Packet
The HIP header values for the UPDATE packet:
Header:
Packet Type = 16
SRC HIT = Sender's HIT
DST HIT = Recipient's HIT
IP ( HIP ( [SEQ, ACK, ] HIP_MAC, HIP_SIGNATURE ) )
Valid control bits: None
The UPDATE packet contains mandatory HIP_MAC and HIP_SIGNATURE
parameters, and other optional parameters.
The UPDATE packet contains zero or one SEQ parameter. The presence
of a SEQ parameter indicates that the receiver MUST acknowledge the
UPDATE. An UPDATE that does not contain a SEQ but only an ACK
parameter is simply an acknowledgment of a previous UPDATE and itself
MUST NOT be acknowledged by a separate ACK parameter. Such UPDATE
packets containing only an ACK parameter do not require processing in
relative order to other UPDATE packets. An UPDATE packet without
either a SEQ or an ACK parameter is invalid; such unacknowledged
updates MUST instead use a NOTIFY packet.
An UPDATE packet contains zero or one ACK parameter. The ACK
parameter echoes the SEQ sequence number of the UPDATE packet being
ACKed. A host MAY choose to acknowledge more than one UPDATE packet
at a time; e.g., the ACK parameter may contain the last two SEQ
values received, for resilience against packet loss. ACK values are
not cumulative; each received unique SEQ value requires at least one
corresponding ACK value in reply. Received ACK parameters that are
redundant are ignored. Hosts MUST implement the processing of ACK
parameters with multiple SEQ sequence numbers even if they do not
implement sending ACK parameters with multiple SEQ sequence numbers.
The UPDATE packet may contain both a SEQ and an ACK parameter. In
this case, the ACK parameter is being piggybacked on an outgoing
UPDATE. In general, UPDATEs carrying SEQ SHOULD be ACKed upon
completion of the processing of the UPDATE. A host MAY choose to
hold the UPDATE carrying an ACK parameter for a short period of time
to allow for the possibility of piggybacking the ACK parameter, in a
manner similar to TCP delayed acknowledgments.
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A sender MAY choose to forego reliable transmission of a particular
UPDATE (e.g., it becomes overcome by events). The semantics are such
that the receiver MUST acknowledge the UPDATE, but the sender MAY
choose to not care about receiving the ACK parameter.
UPDATEs MAY be retransmitted without incrementing SEQ. If the same
subset of parameters is included in multiple UPDATEs with different
SEQs, the host MUST ensure that the receiver's processing of the
parameters multiple times will not result in a protocol error.
5.3.6. NOTIFY - the HIP Notify Packet
The NOTIFY packet MAY be used to provide information to a peer.
Typically, NOTIFY is used to indicate some type of protocol error or
negotiation failure. NOTIFY packets are unacknowledged. The
receiver can handle the packet only as informational, and SHOULD NOT
change its HIP state (see Section 4.4.2) based purely on a received
NOTIFY packet.
The HIP header values for the NOTIFY packet:
Header:
Packet Type = 17
SRC HIT = Sender's HIT
DST HIT = Recipient's HIT, or zero if unknown
IP ( HIP (<NOTIFICATION>i, [HOST_ID, ] HIP_SIGNATURE) )
Valid control bits: None
The NOTIFY packet is used to carry one or more NOTIFICATION
parameters.
5.3.7. CLOSE - the HIP Association Closing Packet
The HIP header values for the CLOSE packet:
Header:
Packet Type = 18
SRC HIT = Sender's HIT
DST HIT = Recipient's HIT
IP ( HIP ( ECHO_REQUEST_SIGNED, HIP_MAC, HIP_SIGNATURE ) )
Valid control bits: None
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The sender MUST include an ECHO_REQUEST_SIGNED used to validate
CLOSE_ACK received in response, and both a HIP_MAC and a signature
(calculated over the whole HIP packet).
The receiver peer MUST reply with a CLOSE_ACK containing an
ECHO_RESPONSE_SIGNED corresponding to the received
ECHO_REQUEST_SIGNED.
5.3.8. CLOSE_ACK - the HIP Closing Acknowledgment Packet
The HIP header values for the CLOSE_ACK packet:
Header:
Packet Type = 19
SRC HIT = Sender's HIT
DST HIT = Recipient's HIT
IP ( HIP ( ECHO_RESPONSE_SIGNED, HIP_MAC, HIP_SIGNATURE ) )
Valid control bits: None
The sender MUST include both an HMAC and signature (calculated over
the whole HIP packet).
The receiver peer MUST validate the ECHO_RESPONSE_SIGNED and validate
both the HIP_MAC and the signature if the receiver has state for a
HIP association.
5.4. ICMP Messages
When a HIP implementation detects a problem with an incoming packet,
and it either cannot determine the identity of the sender of the
packet or does not have any existing HIP association with the sender
of the packet, it MAY respond with an ICMP packet. Any such replies
MUST be rate-limited as described in [RFC4443]. In most cases, the
ICMP packet has the Parameter Problem type (12 for ICMPv4, 4 for
ICMPv6), with the Pointer pointing to the field that caused the ICMP
message to be generated.
5.4.1. Invalid Version
If a HIP implementation receives a HIP packet that has an
unrecognized HIP version number, it SHOULD respond, rate-limited,
with an ICMP packet with type Parameter Problem, with the Pointer
pointing to the Version/RES. byte in the HIP header.
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