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rfc:rfc7166

Internet Engineering Task Force (IETF) M. Bhatia Request for Comments: 7166 Alcatel-Lucent Obsoletes: 6506 V. Manral Category: Standards Track Ionos Corp. ISSN: 2070-1721 A. Lindem

                                                              Ericsson
                                                            March 2014
            Supporting Authentication Trailer for OSPFv3

Abstract

 Currently, OSPF for IPv6 (OSPFv3) uses IPsec as the only mechanism
 for authenticating protocol packets.  This behavior is different from
 authentication mechanisms present in other routing protocols (OSPFv2,
 Intermediate System to Intermediate System (IS-IS), RIP, and Routing
 Information Protocol Next Generation (RIPng)).  In some environments,
 it has been found that IPsec is difficult to configure and maintain
 and thus cannot be used.  This document defines an alternative
 mechanism to authenticate OSPFv3 protocol packets so that OSPFv3 does
 not depend only upon IPsec for authentication.
 The OSPFv3 Authentication Trailer was originally defined in RFC 6506.
 This document obsoletes RFC 6506 by providing a revised definition,
 including clarifications and refinements of the procedures.

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/rfc7166.

Bhatia, et al. Standards Track [Page 1] RFC 7166 Authentication Trailer for OSPFv3 March 2014

Copyright Notice

 Copyright (c) 2014 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 ....................................................3
    1.1. Requirements ...............................................4
    1.2. Summary of Changes from RFC 6506 ...........................4
 2. Proposed Solution ...............................................5
    2.1. AT-Bit in Options Field ....................................5
    2.2. Basic Operation ............................................6
    2.3. IPv6 Source Address Protection .............................6
 3. OSPFv3 Security Association .....................................7
 4. Authentication Procedure ........................................9
    4.1. Authentication Trailer .....................................9
         4.1.1. Sequence Number Wrap ...............................11
    4.2. OSPFv3 Header Checksum and LLS Data Block Checksum ........11
    4.3. Cryptographic Authentication Procedure ....................12
    4.4. Cross-Protocol Attack Mitigation ..........................12
    4.5. Cryptographic Aspects .....................................12
    4.6. Message Verification ......................................15
 5. Migration and Backward Compatibility ...........................16
 6. Security Considerations ........................................17
 7. IANA Considerations ............................................18
 8. References .....................................................19
    8.1. Normative References ......................................19
    8.2. Informative References ....................................19
 Appendix A. Acknowledgments .......................................22

Bhatia, et al. Standards Track [Page 2] RFC 7166 Authentication Trailer for OSPFv3 March 2014

1. Introduction

 Unlike Open Shortest Path First version 2 (OSPFv2) [RFC2328], OSPF
 for IPv6 (OSPFv3) [RFC5340] does not include the AuType and
 Authentication fields in its headers for authenticating protocol
 packets.  Instead, OSPFv3 relies on the IPsec protocols
 Authentication Header (AH) [RFC4302] and Encapsulating Security
 Payload (ESP) [RFC4303] to provide integrity, authentication, and/or
 confidentiality.
 [RFC4552] describes how IPv6 AH and ESP extension headers can be used
 to provide authentication and/or confidentiality to OSPFv3.
 However, there are some environments, e.g., Mobile Ad Hoc Networks
 (MANETs), where IPsec is difficult to configure and maintain; this
 mechanism cannot be used in such environments.
 [RFC4552] discusses, at length, the reasoning behind using manually
 configured keys, rather than some automated key management protocol
 such as Internet Key Exchange version 2 (IKEv2) [RFC5996].  The
 primary problem is the lack of a suitable key management mechanism,
 as OSPFv3 adjacencies are formed on a one-to-many basis and most key
 management mechanisms are designed for a one-to-one communication
 model.  This forces the system administrator to use manually
 configured Security Associations (SAs) and cryptographic keys to
 provide the authentication and, if desired, confidentiality services.
 Regarding replay protection, [RFC4552] states that:
    Since it is not possible using the current standards to provide
    complete replay protection while using manual keying, the proposed
    solution will not provide protection against replay attacks.
 Since there is no replay protection provided, there are a number of
 vulnerabilities in OSPFv3 that have been discussed in [RFC6039].
 While techniques exist to identify ESP-NULL packets [RFC5879], these
 techniques are generally not implemented in the data planes of OSPFv3
 routers.  This makes it very difficult for implementations to examine
 OSPFv3 packets and prioritize certain OSPFv3 packet types, e.g.,
 Hello packets, over the other types.
 This document defines a mechanism that works similarly to OSPFv2
 [RFC5709] to provide authentication to OSPFv3 packets and solves the
 problems related to replay protection and deterministically
 disambiguating different OSPFv3 packets as described above.

Bhatia, et al. Standards Track [Page 3] RFC 7166 Authentication Trailer for OSPFv3 March 2014

 This document adds support for the Secure Hash Algorithms (SHAs)
 defined in the US NIST Secure Hash Standard (SHS), which is specified
 by NIST FIPS 180-4.  [FIPS-180-4] includes SHA-1, SHA-224, SHA-256,
 SHA-384, and SHA-512.  The Hashed Message Authentication Code (HMAC)
 authentication mode defined in NIST FIPS 198-1 [FIPS-198-1] is used.

1.1. Requirements

 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].

1.2. Summary of Changes from RFC 6506

 This document includes the following changes from RFC 6506 [RFC6506]:
 1. Sections 2.2 and 4.2 explicitly state that the Link-Local
    Signaling (LLS) block checksum calculation is omitted when an
    OSPFv3 Authentication Trailer is used for OSPFv3 authentication.
    The LLS data block is included in the authentication digest
    calculation, and computation of a checksum is unnecessary.
    Clarification of this issue was documented in an erratum.
 2. Section 3 previously recommended usage of an expired key for
    transmitted OSPFv3 packets when no valid keys existed.  This
    statement has been removed.
 3. Section 4.5 includes a correction to the key preparation to use
    the Protocol-Specific Authentication Key (Ks) rather than the
    Authentication Key (K) as the initial key (Ko).  This problem was
    also documented in an erratum.
 4. Section 4.5 also includes a discussion of the choice of key length
    to be the hash length (L) rather than the block size (B).  The
    discussion of this choice was included to clarify an issue raised
    in a rejected erratum.
 5. Sections 4.1 and 4.6 indicate that sequence number checking is
    dependent on OSPFv3 packet type in order to account for packet
    prioritization as specified in [RFC4222].  This was an omission
    from RFC 6506 [RFC6506].
 6. Section 4.6 explicitly states that OSPFv3 packets with a
    nonexistent or expired Security Association (SA) will be dropped.
 7. Section 5 includes guidance on the precise actions required for an
    OSPFv3 router providing a backward-compatible transition mode.

Bhatia, et al. Standards Track [Page 4] RFC 7166 Authentication Trailer for OSPFv3 March 2014

2. Proposed Solution

 To perform non-IPsec Cryptographic Authentication, OSPFv3 routers
 append a special data block, henceforth referred to as the
 Authentication Trailer, to the end of the OSPFv3 packets.  The length
 of the Authentication Trailer is not included in the length of the
 OSPFv3 packet but is included in the IPv6 payload length, as shown in
 Figure 1.
  +---------------------+ --              --  +----------------------+
  | IPv6 Payload Length | ^               ^   | IPv6 Payload Length  |
  | PL = OL + LL        | |               |   | PL = OL + LL + AL    |
  |                     | v               v   |                      |
  +---------------------+ --              --  +----------------------+
  | OSPFv3 Header       | ^               ^   | OSPFv3 Header        |
  | Length = OL         | |               |   | Length = OL          |
  |                     | |    OSPFv3     |   |                      |
  |.....................| |    Packet     |   |......................|
  |                     | |    Length     |   |                      |
  | OSPFv3 Packet       | |               |   | OSPFv3 Packet        |
  |                     | v               v   |                      |
  +---------------------+ --              --  +----------------------+
  |                     | ^               ^   |                      |
  | Optional LLS        | |    LLS Data   |   | Optional LLS         |
  | LL = LLS Data       | |    Block      |   | LL = LLS Data        |
  |      Block Length   | v    Length     v   |      Block Length    |
  +---------------------+ --              --  +----------------------+
                                          ^   |                      |
                     AL = PL - (OL + LL)  |   | Authentication       |
                                          |   | AL = Fixed Trailer + |
                                          v   |      Digest Length   |
                                          --  +----------------------+
              Figure 1: Authentication Trailer in OSPFv3
 The presence of the Link-Local Signaling (LLS) [RFC5613] block is
 determined by the L-bit setting in the OSPFv3 Options field in OSPFv3
 Hello and Database Description packets.  If present, the LLS data
 block is included along with the OSPFv3 packet in the Cryptographic
 Authentication computation.

2.1. AT-Bit in Options Field

 RFC 6506 introduced the AT-bit ("AT" stands for "Authentication
 Trailer") into the OSPFv3 Options field.  OSPFv3 routers MUST set the
 AT-bit in OSPFv3 Hello and Database Description packets to indicate
 that all the packets on this link will include an Authentication
 Trailer.  For OSPFv3 Hello and Database Description packets, the

Bhatia, et al. Standards Track [Page 5] RFC 7166 Authentication Trailer for OSPFv3 March 2014

 AT-bit indicates that the AT is present.  For other OSPFv3 packet
 types, the OSPFv3 AT-bit setting from the OSPFv3 Hello/Database
 Description setting is preserved in the OSPFv3 neighbor data
 structure.  OSPFv3 packet types that don't include an OSPFv3 Options
 field will use the setting from the neighbor data structure to
 determine whether or not the AT is expected.
          0                   1                      2
          0 1 2 3 4 5 6 7 8 9 0 1 2 3  4 5  6 7 8  9 0 1  2 3
         +-+-+-+-+-+-+-+-+-+-+-+-+-+--+-+--+-+-+--+-+-+--+-+--+
         | | | | | | | | | | | | | |AT|L|AF|*|*|DC|R|N|MC|E|V6|
         +-+-+-+-+-+-+-+-+-+-+-+-+-+--+-+--+-+-+--+-+-+--+-+--+
                    Figure 2: OSPFv3 Options Field
 The AT-bit, as shown in the figure above, MUST be set in all OSPFv3
 Hello and Database Description packets that contain an Authentication
 Trailer.

2.2. Basic Operation

 The procedure followed for computing the Authentication Trailer is
 much the same as those described in [RFC5709] and [RFC2328].  One
 difference is that the LLS data block, if present, is included in the
 Cryptographic Authentication computation.
 The way the authentication data is carried in the Authentication
 Trailer is very similar to how it is done in the case of [RFC2328].
 The only difference between the OSPFv2 Authentication Trailer and the
 OSPFv3 Authentication Trailer is that information in addition to the
 message digest is included.  The additional information in the OSPFv3
 Authentication Trailer is included in the message digest computation
 and is therefore protected by OSPFv3 Cryptographic Authentication as
 described herein.
 Consistent with OSPFv2 Cryptographic Authentication [RFC2328] and
 Link-Local Signaling Cryptographic Authentication [RFC5613], checksum
 calculation and verification are omitted for both the OSPFv3 header
 checksum and the LLS data block when the OSPFv3 authentication
 mechanism described in this specification is used.

2.3. IPv6 Source Address Protection

 While OSPFv3 always uses the Router ID to identify OSPFv3 neighbors,
 the IPv6 source address is learned from OSPFv3 Hello packets and
 copied into the neighbor data structure [RFC5340].  Hence, OSPFv3 is
 susceptible to Man-in-the-Middle attacks where the IPv6 source
 address is modified.  To thwart such attacks, the IPv6 source address

Bhatia, et al. Standards Track [Page 6] RFC 7166 Authentication Trailer for OSPFv3 March 2014

 will be included in the message digest calculation and protected by
 OSPFv3 authentication.  Refer to Section 4.5 for details.  This is
 different than the procedure specified in [RFC5709] but consistent
 with [MANUAL-KEY].

3. OSPFv3 Security Association

 An OSPFv3 Security Association (SA) contains a set of parameters
 shared between any two legitimate OSPFv3 speakers.
 Parameters associated with an OSPFv3 SA are as follows:
 o  Security Association Identifier (SA ID)
    This is a 16-bit unsigned integer used to uniquely identify an
    OSPFv3 SA, as manually configured by the network operator.
    The receiver determines the active SA by looking at the SA ID
    field in the incoming protocol packet.
    The sender, based on the active configuration, selects an SA to
    use and puts the correct Key ID value associated with the SA in
    the OSPFv3 protocol packet.  If multiple valid and active OSPFv3
    SAs exist for a given interface, the sender may use any of those
    SAs to protect the packet.
    Using SA IDs makes changing keys while maintaining protocol
    operation convenient.  Each SA ID specifies two independent parts:
    the authentication algorithm and the Authentication Key, as
    explained below.
    Normally, an implementation would allow the network operator to
    configure a set of keys in a key chain, with each key in the chain
    having a fixed lifetime.  The actual operation of these mechanisms
    is outside the scope of this document.
    Note that each SA ID can indicate a key with a different
    authentication algorithm.  This allows the introduction of new
    authentication mechanisms without disrupting existing OSPFv3
    adjacencies.
 o  Authentication Algorithm
    This signifies the authentication algorithm to be used with this
    OSPFv3 SA.  This information is never sent in clear text over the
    wire.  Because this information is not sent on the wire, the
    implementer chooses an implementation-specific representation for
    this information.

Bhatia, et al. Standards Track [Page 7] RFC 7166 Authentication Trailer for OSPFv3 March 2014

    Currently, the following algorithms are supported:
  • HMAC-SHA-1,
  • HMAC-SHA-256,
  • HMAC-SHA-384, and
  • HMAC-SHA-512.
 o  Authentication Key
    This value denotes the Cryptographic Authentication Key associated
    with this OSPFv3 SA.  The length of this key is variable and
    depends upon the authentication algorithm specified by the
    OSPFv3 SA.
 o  KeyStartAccept
    This value indicates the time that this OSPFv3 router will accept
    packets that have been created with this OSPFv3 SA.
 o  KeyStartGenerate
    This value indicates the time that this OSPFv3 router will begin
    using this OSPFv3 SA for OSPFv3 packet generation.
 o  KeyStopGenerate
    This value indicates the time that this OSPFv3 router will stop
    using this OSPFv3 SA for OSPFv3 packet generation.
 o  KeyStopAccept
    This value indicates the time that this OSPFv3 router will stop
    accepting packets generated with this OSPFv3 SA.
    In order to achieve smooth key transition, KeyStartAccept SHOULD
    be less than KeyStartGenerate, and KeyStopGenerate SHOULD be less
    than KeyStopAccept.  If KeyStartGenerate or KeyStartAccept is left
    unspecified, the time will default to 0, and the key will be used
    immediately.  If KeyStopGenerate or KeyStopAccept is left
    unspecified, the time will default to infinity, and the key's
    lifetime will be infinite.  When a new key replaces an old key,
    the KeyStartGenerate time for the new key MUST be less than or
    equal to the KeyStopGenerate time of the old key.

Bhatia, et al. Standards Track [Page 8] RFC 7166 Authentication Trailer for OSPFv3 March 2014

    Key storage SHOULD persist across a system restart, warm or cold,
    to avoid operational issues.  In the event that the last key
    associated with an interface expires, the network operator SHOULD
    be notified, and the OSPFv3 packet MUST NOT be transmitted
    unauthenticated.

4. Authentication Procedure

4.1. Authentication Trailer

 The Authentication Trailer that is appended to the OSPFv3 protocol
 packet is described below:
   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
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |      Authentication Type      |        Auth Data Len          |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |           Reserved            |   Security Association ID     |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |           Cryptographic Sequence Number (High-Order 32 Bits)  |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |           Cryptographic Sequence Number (Low-Order 32 Bits)   |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                                                               |
  |                Authentication Data (Variable)                 |
  ~                                                               ~
  |                                                               |
  |                                                               |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                Figure 3: Authentication Trailer Format
 The various fields in the Authentication Trailer are as follows:
 o  Authentication Type
    This 16-bit field identifies the type of authentication.  The
    following values are defined in this specification:
       0 - Reserved.
       1 - HMAC Cryptographic Authentication as described herein.
 o  Auth Data Len
    This is the length in octets of the Authentication Trailer (AT),
    including both the 16-octet fixed header and the variable-length
    message digest.

Bhatia, et al. Standards Track [Page 9] RFC 7166 Authentication Trailer for OSPFv3 March 2014

 o  Reserved
    This field is reserved.  It SHOULD be set to 0 when sending
    protocol packets and MUST be ignored when receiving protocol
    packets.
 o  Security Association Identifier (SA ID)
    This 16-bit field maps to the authentication algorithm and the
    secret key used to create the message digest appended to the
    OSPFv3 protocol packet.
    Though the SA ID implies the algorithm, the HMAC output size
    should not be used by implementers as an implicit hint, because
    additional algorithms may be defined in the future that have the
    same output size.
 o  Cryptographic Sequence Number
    This is a 64-bit strictly increasing sequence number that is used
    to guard against replay attacks.  The 64-bit sequence number MUST
    be incremented for every OSPFv3 packet sent by the OSPFv3 router.
    Upon reception, the sequence number MUST be greater than the
    sequence number in the last accepted OSPFv3 packet of the same
    OSPFv3 packet type from the sending OSPFv3 neighbor.  Otherwise,
    the OSPFv3 packet is considered a replayed packet and dropped.
    OSPFv3 packets of different types may arrive out of order if they
    are prioritized as recommended in [RFC4222].
    OSPFv3 routers implementing this specification MUST use available
    mechanisms to preserve the sequence number's strictly increasing
    property for the deployed life of the OSPFv3 router (including
    cold restarts).  One mechanism for accomplishing this would be to
    use the high-order 32 bits of the sequence number as a wrap/boot
    count that is incremented anytime the OSPFv3 router loses its
    sequence number state.  Sequence number wrap is described in
    Section 4.1.1.
 o  Authentication Data
    This field contains variable data that is carrying the digest for
    the protocol packet and optional LLS data block.

Bhatia, et al. Standards Track [Page 10] RFC 7166 Authentication Trailer for OSPFv3 March 2014

4.1.1. Sequence Number Wrap

 When incrementing the sequence number for each transmitted OSPFv3
 packet, the sequence number should be treated as an unsigned 64-bit
 value.  If the lower-order 32-bit value wraps, the higher-order
 32-bit value should be incremented and saved in non-volatile storage.
 If by some chance the OSPFv3 router is deployed long enough that
 there is a possibility that the 64-bit sequence number may wrap, all
 keys, independent of their key distribution mechanism, MUST be reset
 to avoid the possibility of replay attacks.  Once the keys have been
 changed, the higher-order sequence number can be reset to 0 and saved
 to non-volatile storage.

4.2. OSPFv3 Header Checksum and LLS Data Block Checksum

 Both the checksum calculation and verification are omitted for the
 OSPFv3 header checksum and the LLS data block checksum [RFC5613] when
 the OSPFv3 authentication mechanism described in this specification
 is used.  This implies the following:
 o  For OSPFv3 packets to be transmitted, the OSPFv3 header checksum
    computation is omitted, and the OSPFv3 header checksum SHOULD be
    set to 0 prior to computation of the OSPFv3 Authentication Trailer
    message digest.
 o  For OSPFv3 packets including an LLS data block to be transmitted,
    the OSPFv3 LLS data block checksum computation is omitted, and the
    OSPFv3 LLS data block checksum SHOULD be set to 0 prior to
    computation of the OSPFv3 Authentication Trailer message digest.
 o  For received OSPFv3 packets including an OSPFv3 Authentication
    Trailer, OSPFv3 header checksum verification MUST be omitted.
    However, if the OSPFv3 packet does include a non-zero OSPFv3
    header checksum, it will not be modified by the receiver and will
    simply be included in the OSPFv3 Authentication Trailer message
    digest verification.
 o  For received OSPFv3 packets including an LLS data block and OSPFv3
    Authentication Trailer, LLS data block checksum verification MUST
    be omitted.  However, if the OSPFv3 packet does include an LLS
    data block with a non-zero checksum, it will not be modified by
    the receiver and will simply be included in the OSPFv3
    Authentication Trailer message digest verification.

Bhatia, et al. Standards Track [Page 11] RFC 7166 Authentication Trailer for OSPFv3 March 2014

4.3. Cryptographic Authentication Procedure

 As noted earlier, the SA ID maps to the authentication algorithm and
 the secret key used to generate and verify the message digest.  This
 specification discusses the computation of OSPFv3 Cryptographic
 Authentication data when any of the NIST SHS family of algorithms is
 used in the Hashed Message Authentication Code (HMAC) mode.
 The currently valid algorithms (including mode) for OSPFv3
 Cryptographic Authentication include:
 o  HMAC-SHA-1,
 o  HMAC-SHA-256,
 o  HMAC-SHA-384, and
 o  HMAC-SHA-512.
 Of the above, implementations of this specification MUST include
 support for at least HMAC-SHA-256 and SHOULD include support for
 HMAC-SHA-1 and MAY also include support for HMAC-SHA-384 and
 HMAC-SHA-512.
 Implementations of this specification MUST use HMAC-SHA-256 as the
 default authentication algorithm.

4.4. Cross-Protocol Attack Mitigation

 In order to prevent cross-protocol replay attacks for protocols
 sharing common keys, the two-octet OSPFv3 Cryptographic Protocol ID
 is appended to the Authentication Key prior to use.  Other protocols
 using Cryptographic Authentication as specified herein MUST similarly
 append their respective Cryptographic Protocol IDs to their keys in
 this step.  Refer to the IANA Considerations (Section 7).

4.5. Cryptographic Aspects

 In the algorithm description below, the following nomenclature, which
 is consistent with [FIPS-198-1], is used:
 H is the specific hashing algorithm (e.g., SHA-256).
 K is the Authentication Key from the OSPFv3 Security Association.
 Ks is a Protocol-Specific Authentication Key obtained by appending
 Authentication Key (K) with the two-octet OSPFv3 Cryptographic
 Protocol ID.

Bhatia, et al. Standards Track [Page 12] RFC 7166 Authentication Trailer for OSPFv3 March 2014

 Ko is the cryptographic key used with the hash algorithm.
 B is the block size of H, measured in octets rather than bits.  Note
 that B is the internal block size, not the hash size.
    For SHA-1 and SHA-256: B == 64
    For SHA-384 and SHA-512: B == 128
 L is the length of the hash, measured in octets rather than bits.
 XOR is the exclusive-or operation.
 Opad is the hexadecimal value 0x5c repeated B times.
 Ipad is the hexadecimal value 0x36 repeated B times.
 Apad is a value that is the same length as the hash output or message
 digest.  The first 16 octets contain the IPv6 source address followed
 by the hexadecimal value 0x878FE1F3 repeated (L-16)/4 times.  This
 implies that hash output is always a length of at least 16 octets.
 1. Preparation of the Key
    The OSPFv3 Cryptographic Protocol ID is appended to the
    Authentication Key (K), yielding a Protocol-Specific
    Authentication Key (Ks).  In this application, Ko is always
    L octets long.  While [RFC2104] supports a key that is up to
    B octets long, this application uses L as the Ks length consistent
    with [RFC4822], [RFC5310], and [RFC5709].  According to
    [FIPS-198-1], Section 3, keys greater than L octets do not
    significantly increase the function strength.  Ks is computed as
    follows:
       If Ks is L octets long, then Ko is equal to Ks.  If Ks is more
       than L octets long, then Ko is set to H(Ks).  If Ks is less
       than L octets long, then Ko is set to the value of Ks, with
       zeros appended to the end of Ks such that Ko is L octets long.
 2. First-Hash
    First, the OSPFv3 packet's Authentication Data field in the
    Authentication Trailer is filled with the value Apad.  This is
    very similar to the appendage described in [RFC2328],
    Appendix D.4.3, Items (6)(a) and (6)(d)).

Bhatia, et al. Standards Track [Page 13] RFC 7166 Authentication Trailer for OSPFv3 March 2014

    Then, a First-Hash, also known as the inner hash, is computed as
    follows:
       First-Hash = H(Ko XOR Ipad || (OSPFv3 Packet))
       When XORing Ko and Ipad, Ko will be padded with zeros to the
       length of Ipad.
       Implementation Note: The First-Hash above includes the
       Authentication Trailer as well as the OSPFv3 packet as per
       [RFC2328], Appendix D.4.3, and the LLS data block, if present
       [RFC5613].
    The definition of Apad (above) ensures that it is always the same
    length as the hash output.  This is consistent with RFC 2328.
    Note that the "(OSPFv3 Packet)" referenced in the First-Hash
    function above includes both the optional LLS data block and the
    OSPFv3 Authentication Trailer.
    The digest length for SHA-1 is 20 octets; for SHA-256, 32 octets;
    for SHA-384, 48 octets; and for SHA-512, 64 octets.
 3. Second-Hash
    Then a Second-Hash, also known as the outer hash, is computed as
    follows:
       Second-Hash = H(Ko XOR Opad || First-Hash)
       When XORing Ko and Opad, Ko will be padded with zeros to the
       length of Opad.
 4. Result
    The resulting Second-Hash becomes the authentication data that is
    sent in the Authentication Trailer of the OSPFv3 packet.  The
    length of the authentication data is always identical to the
    message digest size of the specific hash function H that is
    being used.
    This also means that the use of hash functions with larger output
    sizes will also increase the size of the OSPFv3 packet as
    transmitted on the wire.

Bhatia, et al. Standards Track [Page 14] RFC 7166 Authentication Trailer for OSPFv3 March 2014

       Implementation Note: [RFC2328], Appendix D specifies that the
       Authentication Trailer is not counted in the OSPF packet's own
       Length field but is included in the packet's IP Length field.
       Similar to this, the Authentication Trailer is not included in
       the OSPFv3 header length but is included in the IPv6 header
       payload length.

4.6. Message Verification

 A router would determine that OSPFv3 is using an Authentication
 Trailer (AT) by examining the AT-bit in the Options field in the
 OSPFv3 header for Hello and Database Description packets.  The
 specification in the Hello and Database Description options indicates
 that other OSPFv3 packets will include the Authentication Trailer.
 The AT is accessed using the OSPFv3 packet header length to access
 the data after the OSPFv3 packet and, if an LLS data block [RFC5613]
 is present, using the LLS data block length to access the data after
 the LLS data block.  The L-bit in the OSPFv3 options in Hello and
 Database Description packets is examined to determine if an LLS data
 block is present.  If an LLS data block is present (as specified by
 the L-bit), it is included along with the OSPFv3 Hello or Database
 Description packet in the Cryptographic Authentication computation.
 Due to the placement of the AT following the LLS data block and the
 fact that the LLS data block is included in the Cryptographic
 Authentication computation, OSPFv3 routers supporting this
 specification MUST minimally support examining the L-bit in the
 OSPFv3 options and using the length in the LLS data block to access
 the AT.  It is RECOMMENDED that OSPFv3 routers supporting this
 specification fully support OSPFv3 Link-Local Signaling [RFC5613].
 If usage of the AT, as specified herein, is configured for an OSPFv3
 link, OSPFv3 Hello and Database Description packets with the AT-bit
 clear in the options will be dropped.  All OSPFv3 packet types will
 be dropped if the AT is configured for the link and the IPv6 header
 length is less than the amount necessary to include an Authentication
 Trailer.
 The receiving interface's OSPFv3 SA is located using the SA ID in the
 received AT.  If the SA is not found, or if the SA is not valid for
 reception (i.e., current time < KeyStartAccept or
 current time >= KeyStopAccept), the OSPFv3 packet is dropped.
 If the cryptographic sequence number in the AT is less than or equal
 to the last sequence number in the last OSPFv3 packet of the same
 OSPFv3 type successfully received from the neighbor, the OSPFv3

Bhatia, et al. Standards Track [Page 15] RFC 7166 Authentication Trailer for OSPFv3 March 2014

 packet MUST be dropped, and an error event SHOULD be logged.  OSPFv3
 packets of different types may arrive out of order if they are
 prioritized as recommended in [RFC4222].
 Authentication-algorithm-dependent processing needs to be performed,
 using the algorithm specified by the appropriate OSPFv3 SA for the
 received packet.
 Before an implementation performs any processing, it needs to save
 the values of the Authentication Data field from the Authentication
 Trailer appended to the OSPFv3 packet.
 It should then set the Authentication Data field with Apad before the
 authentication data is computed (as described in Section 4.5).  The
 calculated data is compared with the received authentication data in
 the Authentication Trailer.  If the two do not match, the packet MUST
 be discarded, and an error event SHOULD be logged.
 After the OSPFv3 packet has been successfully authenticated,
 implementations MUST store the 64-bit cryptographic sequence number
 for each OSPFv3 packet type received from the neighbor.  The saved
 cryptographic sequence numbers will be used for replay checking for
 subsequent packets received from the neighbor.

5. Migration and Backward Compatibility

 All OSPFv3 routers participating on a link SHOULD be migrated to
 OSPFv3 authentication at the same time.  As with OSPFv2
 authentication, a mismatch in the SA ID, Authentication Type, or
 message digest will result in failure to form an adjacency.  For
 multi-access links, communities of OSPFv3 routers could be migrated
 using different Interface Instance IDs.  However, at least one router
 would need to form adjacencies between both the OSPFv3 routers
 including and not including the Authentication Trailer.  This would
 result in sub-optimal routing as well as added complexity and is only
 recommended in cases where authentication is desired on the link and
 migrating all the routers on the link at the same time isn't
 feasible.
 In support of uninterrupted deployment, an OSPFv3 router implementing
 this specification MAY implement a transition mode where it includes
 the Authentication Trailer in transmitted packets but does not verify
 this information in received packets.  This is provided as a

Bhatia, et al. Standards Track [Page 16] RFC 7166 Authentication Trailer for OSPFv3 March 2014

 transition aid for networks in the process of migrating to the
 authentication mechanism described in this specification.  More
 specifically:
 1. OSPFv3 routers in transition mode will include the OSPFv3
    Authentication Trailer in transmitted packets and set the AT-bit
    in the Options field of transmitted Hello and Database Description
    packets.  OSPFv3 routers receiving these packets and not having
    authentication configured will ignore the Authentication Trailer
    and AT-bit.
 2. OSPFv3 routers in transition mode will also calculate and set the
    OSPFv3 header checksum and the LLS data block checksum in
    transmitted packets so that they will not be dropped by OSPFv3
    routers without authentication configured.
 3. OSPFv3 routers in transition mode will authenticate received
    packets that either have the AT-bit set in the Options field for
    Hello or Database Description packets or are from a neighbor that
    previously set the AT-bit in the Options field of successfully
    authenticated Hello and Database Description packets.
 4. OSPFv3 routers in transition mode will also accept packets without
    the Options field AT-bit set in Hello and Database Description
    packets.  These packets will be assumed to be from OSPFv3 routers
    without authentication configured, and they will not be
    authenticated.  Additionally, the OSPFv3 header checksum and LLS
    data block checksum will be validated.

6. Security Considerations

 This document proposes extensions to OSPFv3 that would make it more
 secure than OSPFv3 as defined in [RFC5340].  It does not provide
 confidentiality, as a routing protocol contains information that does
 not need to be kept secret.  It does, however, provide means to
 authenticate the sender of packets that are of interest.  It
 addresses all the security issues that have been identified in
 [RFC6039] and [RFC6506].
 It should be noted that the authentication method described in this
 document is not being used to authenticate the specific originator of
 a packet but rather is being used to confirm that the packet has
 indeed been issued by a router that has access to the
 Authentication Key.
 Deployments SHOULD use sufficiently long and random values for the
 Authentication Key so that guessing and other cryptographic attacks
 on the key are not feasible in their environments.  Furthermore, it

Bhatia, et al. Standards Track [Page 17] RFC 7166 Authentication Trailer for OSPFv3 March 2014

 is RECOMMENDED that Authentication Keys incorporate at least 128
 pseudorandom bits to minimize the risk of such attacks.  In support
 of these recommendations, management systems SHOULD support
 hexadecimal input of Authentication Keys.
 Deployments that support a transitionary state but interoperate with
 routers that do not support this authentication method may be exposed
 to unauthenticated data during the transition period.
 The mechanism described herein is not perfect and does not need to be
 perfect.  Instead, this mechanism represents a significant increase
 in the effort required for an adversary to successfully attack the
 OSPFv3 protocol, while not causing undue implementation, deployment,
 or operational complexity.
 Refer to [RFC4552] for additional considerations on manual keying.

7. IANA Considerations

 This document obsoletes RFC 6506; thus, IANA has updated the
 references in existing registries that pointed to RFC 6506 to point
 to this document.  This is the only IANA action requested by this
 document.
 IANA previously allocated the AT-bit (0x000400) in the "OSPFv3
 Options (24 bits)" registry as described in Section 2.1.
 IANA previously created the "Open Shortest Path First v3 (OSPFv3)
 Authentication Trailer Options" registry.  This registry includes the
 "OSPFv3 Authentication Types" registry, which defines valid values
 for the Authentication Type field in the OSPFv3 Authentication
 Trailer.  The registration procedure is Standards Action [RFC5226].
         +-------------+-----------------------------------+
         |Value        | Designation                       |
         +-------------+-----------------------------------+
         | 0           | Reserved                          |
         |             |                                   |
         | 1           | HMAC Cryptographic Authentication |
         |             |                                   |
         | 2-65535     | Unassigned                        |
         +-------------+-----------------------------------+
                      OSPFv3 Authentication Types
 Finally, IANA previously created the "Keying and Authentication for
 Routing Protocols (KARP) Parameters" registry.  This registry
 includes the "Cryptographic Protocol ID" registry, which provides

Bhatia, et al. Standards Track [Page 18] RFC 7166 Authentication Trailer for OSPFv3 March 2014

 unique protocol-specific values for cryptographic applications,
 including but not limited to prevention of cross-protocol replay
 attacks.  Values can be assigned for both native IPv4/IPv6 protocols
 and UDP/TCP protocols.  The registration procedure is Standards
 Action.
                +-------------+----------------------+
                | Value/Range | Designation          |
                +-------------+----------------------+
                | 0           | Reserved             |
                |             |                      |
                | 1           | OSPFv3               |
                |             |                      |
                | 2-65535     | Unassigned           |
                +-------------+----------------------+
                       Cryptographic Protocol ID

8. References

8.1. Normative References

 [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", BCP 14, RFC 2119, March 1997.
 [RFC2328]  Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998.
 [RFC5340]  Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
            for IPv6", RFC 5340, July 2008.
 [RFC5709]  Bhatia, M., Manral, V., Fanto, M., White, R., Barnes, M.,
            Li, T., and R. Atkinson, "OSPFv2 HMAC-SHA Cryptographic
            Authentication", RFC 5709, October 2009.

8.2. Informative References

 [FIPS-180-4]
            US National Institute of Standards and Technology, "Secure
            Hash Standard (SHS)", FIPS PUB 180-4, March 2012.
 [FIPS-198-1]
            US National Institute of Standards and Technology, "The
            Keyed-Hash Message Authentication Code (HMAC)", FIPS
            PUB 198-1, July 2008.

Bhatia, et al. Standards Track [Page 19] RFC 7166 Authentication Trailer for OSPFv3 March 2014

 [MANUAL-KEY]
            Bhatia, M., Hartman, S., and D. Zhang, "Security Extension
            for OSPFv2 when using Manual Key Management", Work in
            Progress, February 2011.
 [RFC2104]  Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-
            Hashing for Message Authentication", RFC 2104,
            February 1997.
 [RFC4222]  Choudhury, G., Ed., "Prioritized Treatment of Specific
            OSPF Version 2 Packets and Congestion Avoidance", BCP 112,
            RFC 4222, October 2005.
 [RFC4302]  Kent, S., "IP Authentication Header", RFC 4302,
            December 2005.
 [RFC4303]  Kent, S., "IP Encapsulating Security Payload (ESP)",
            RFC 4303, December 2005.
 [RFC4552]  Gupta, M. and N. Melam, "Authentication/Confidentiality
            for OSPFv3", RFC 4552, June 2006.
 [RFC4822]  Atkinson, R. and M. Fanto, "RIPv2 Cryptographic
            Authentication", RFC 4822, February 2007.
 [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
            IANA Considerations Section in RFCs", BCP 26, RFC 5226,
            May 2008.
 [RFC5310]  Bhatia, M., Manral, V., Li, T., Atkinson, R., White, R.,
            and M. Fanto, "IS-IS Generic Cryptographic
            Authentication", RFC 5310, February 2009.
 [RFC5613]  Zinin, A., Roy, A., Nguyen, L., Friedman, B., and D.
            Yeung, "OSPF Link-Local Signaling", RFC 5613, August 2009.
 [RFC5879]  Kivinen, T. and D. McDonald, "Heuristics for Detecting
            ESP-NULL Packets", RFC 5879, May 2010.
 [RFC5996]  Kaufman, C., Hoffman, P., Nir, Y., and P. Eronen,
            "Internet Key Exchange Protocol Version 2 (IKEv2)",
            RFC 5996, September 2010.

Bhatia, et al. Standards Track [Page 20] RFC 7166 Authentication Trailer for OSPFv3 March 2014

 [RFC6039]  Manral, V., Bhatia, M., Jaeggli, J., and R. White, "Issues
            with Existing Cryptographic Protection Methods for Routing
            Protocols", RFC 6039, October 2010.
 [RFC6506]  Bhatia, M., Manral, V., and A. Lindem, "Supporting
            Authentication Trailer for OSPFv3", RFC 6506,
            February 2012.

Bhatia, et al. Standards Track [Page 21] RFC 7166 Authentication Trailer for OSPFv3 March 2014

Appendix A. Acknowledgments

 First and foremost, thanks to the US National Institute of Standards
 and Technology for their work on the SHA [FIPS-180-4] and HMAC
 [FIPS-198-1].
 Thanks also need to go to the authors of the HMAC-SHA authentication
 RFCs, including [RFC4822], [RFC5310], and [RFC5709].  The basic
 HMAC-SHA procedures were originally described by Ran Atkinson in
 [RFC4822].
 Also, thanks to Ran Atkinson for help in the analysis of RFC 6506
 errata.
 Thanks to Srinivasan K L and Marek Karasek for their identification
 and submission of RFC 6506 errata.
 Thanks to Sam Hartman for discussions on replay mitigation and the
 use of a 64-bit strictly increasing sequence number.  Also, thanks to
 Sam for comments during IETF last call with respect to the OSPFv3 SA
 and the sharing of keys between protocols.
 Thanks to Michael Barnes for numerous comments and strong input on
 the coverage of LLS by the Authentication Trailer (AT).
 Thanks to Marek Karasek for providing the specifics with respect to
 backward-compatible transition mode.
 Thanks to Michael Dubrovskiy and Anton Smirnov for comments on
 document revisions.
 Thanks to Rajesh Shetty for numerous comments, including the
 suggestion to include an Authentication Type field in the
 Authentication Trailer for extendibility.
 Thanks to Uma Chunduri for suggesting that we may want to protect the
 IPv6 source address even though OSPFv3 uses the Router ID for
 neighbor identification.
 Thanks to Srinivasan K L, Shraddha H, Alan Davey, Russ White, Stan
 Ratliff, and Glen Kent for their support and review comments.
 Thanks to Alia Atlas for comments made under the purview of the
 Routing Directorate review.
 Thanks to Stephen Farrell for comments during the IESG review.
 Stephen was also involved in the discussion of cross-protocol
 attacks.

Bhatia, et al. Standards Track [Page 22] RFC 7166 Authentication Trailer for OSPFv3 March 2014

 Thanks to Brian Carpenter for comments made during the Gen-ART
 review.
 Thanks to Victor Kuarsingh for the OPS-DIR review.
 Thanks to Brian Weis for the SEC-DIR review.

Authors' Addresses

 Manav Bhatia
 Alcatel-Lucent
 Bangalore
 India
 EMail: manav.bhatia@alcatel-lucent.com
 Vishwas Manral
 Ionos Corp.
 4100 Moorpark Ave.
 San Jose, CA  95117
 USA
 EMail: vishwas@ionosnetworks.com
 Acee Lindem
 Ericsson
 301 Midenhall Way
 Cary, NC  27513
 USA
 EMail: acee.lindem@ericsson.com

Bhatia, et al. Standards Track [Page 23]

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