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Versions: 00 01 02 03 04 05 06 07 rfc5310                               
Internet Draft IS-IS HMAC SHA Cryptographic Authentication February 2007

   Network Working Group                                   Manav Bhatia
   Internet Draft                                   Lucent Technologies
   Expires: August 2007                                  Vishwas Manral
                                                            IP Infusion
                                                             Russ White
                                                          Cisco Systems

                IS-IS HMAC SHA Cryptographic Authentication


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   This document proposes an extension to IS-IS to allow the use of any
   cryptographic authentication algorithm in addition to the already
   documented authentication schemes, described in the base
   specification and RFC 3567.

   Although this document has been written specifically for using MAC
   construct along with the SHA family of cryptographic hash functions,
   the method described in this document is generic and can be used to
   extend IS-IS to support any cryptographic hash function in the

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Conventions used in this document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [KEYWORDS]

1. Introduction

   IS-IS [ISO] [RFC1195] specification allows for authentication of its
   PDUs via the authentication TLV 10 that is carried as the part of the
   PDU. The base spec has provision for only clear text passwords and
   RFC 3567 [RFC3567] augments this to provide the capability to use
   HMAC MD5 authentication for its PDUs.

   The first octet of value field of TLV 10 specifies the type of
   authentication to be carried out. Type 0 is reserved, Type 1
   indicates a cleartext password, Type 54 indicates HMAC MD5 and Type
   255 is used for routing domain private authentication methods. The
   remainder of the value field contains the actual authentication data
   determined by the value of the authentication type.

   This document proposes a new authentication type to be carried in TLV
   10, called the cryptographic authentication (CRYPTO_AUTH). This can
   be used to specify any authentication algorithm for authenticating
   and verifying IS-IS PDUs.

   This document also explains how HMAC-SHA authentication can be used
   in IS-IS.

   By definition, HMAC [RFC2104] requires a cryptographic hash function.
   We propose to use any one of SHA-1, SHA-224, SHA-256, SHA-384 and
   SHA-512 [NIST] for this purpose to authenticate the IS-IS PDUs.

   We propose to do away with the per interface keys and instead have
   key IDs that map to unique IS-IS Security Associations.

2. IS-IS Security Association

   An IS-IS Security Association (SA) contains a set of shared
   parameters between any two legitimate IS-IS speakers.

   Parameters associated with an IS-IS SA:

   O Key ID – This is a one octet unsigned integer used to uniquely
   identify an IS-IS SA, as manually configured by the network operator.
   The receiver determines the active SA by looking at this field in the
   incoming PDU. The sender puts this Key ID based on the active

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   Using key IDs makes changing keys while maintaining protocol
   operation convenient. Each key ID specifies two independent parts,
   the authentication protocol 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 fixed lifetime. The actual operation of these mechanisms is
   outside the scope of this document.

   Note that each key ID can indicate a key with a different
   authentication protocol. This allows multiple authentication
   mechanisms to be used at various times without disrupting IS-IS
   peering, including the introduction of new authentication mechanisms.

   o Authentication Algorithm – This signifies the authentication
   algorithm to be used with the IS-IS SA. Valid values are HMAC-SHA-1,
   HMAC-SHA-224, HMAC-SHA-256, HMAC-SHA-384 and HMAC-SHA-512.

   o Authentication Key – This value denotes the key associated with the
   IS-IS SA. The length of this key is variable and depends upon the
   authentication algorithm specified by the IS-IS SA.

3. Authentication Procedures

3.1 Authentication TLV

   A new authentication code, [TB assigned by IANA], indicates the
   CRYPTO_AUTH mechanism described in this document is in use, is
   inserted in the first octet of the existing IS-IS Authentication TLV
                   0                   1
                   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
                   |     Type 10   |     Length    |
                   |   Auth Type   |     Key ID    |
                   |                               |
                   +                               +
                   | Authentication Data (Variable)|
                   +                               +
                   |                               |
                                Figure 1

3.2 Procedures at the Sending Side

   An appropriate IS-IS SA is selected for use with an outgoing IS-IS
   PDU. This is done based on the active key at that instant. If IS-IS
   is unable to find an active key, then the PDU is discarded.

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   If IS-IS is able to find the active key, then the key gives the
   authentication algorithm (HMAC-SHA-1, HMAC-SHA-224, HMAC-SHA-256,
   HMAC-SHA-384 or HMAC-SHA-512) that needs to be applied on the PDU.

   An implementation MUST fill the authentication type and the length
   before the authentication data is computed. The length of the TLV is
   set as per the authentication algorithm that is being used.

   It’s set to 22 for HMAC-SHA-1, 30 for HMAC-SHA-224, 34 for HMAC-SHA-
   256, 50 for HMAC-SHA-384 and 66 for HMAC-SHA-512. Note that one octet
   has been added to account for the Key ID and one octet for the
   authentication type. The authentication value field is set to Zero.

   The key ID is filled.

   The checksum and remaining life time fields are set to Zero for the
   LSPs before authentication is calculated.

   The result of the authentication algorithm is placed in the
   Authentication data, following the key ID.

   The authentication data for the IS-IS IIH PDUs MUST be computed after
   the IIH has been padded to the MTU size, if padding is not explicitly

3.3 Procedure at the Receiving Side

   The appropriate IS-IS SA is identified by looking at the Key ID from
   the Authentication TLV 10 from the incoming IS-IS PDU.

   Authentication algorithm dependent processing, needs to be performed,
   using the algorithm specified by the appropriate IS-IS SA for the
   received packet.

   Before an implementation performs any processing it needs to save the
   values of the Authentication value field, the checksum and the
   remaining life time.

   These fields are set to Zero and the authentication data is computed.
   The calculated data is compared with the received authentication data
   in the PDU and the PDU is discarded if the two do not match. In such
   a case, an error event SHOULD be logged.

   An implementation MAY have a transition mode where it includes
   CRYPTO_AUTH information in the PDUs but does not verify this
   information. This is provided as a transition aid for networks in the
   process of migrating to the new CRYPTO_AUTH based authentication

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   Similarly, implementations not supporting the CRYPTO_AUTH field MAY
   accept PDUs that contain this particular field in TLV 10.

4. Algorithm Dependent Processing

   HMAC is a mechanism for message authentication using cryptographic
   hash functions and has been explained in depth in [RFC2104]. The
   reader is suggested to go through it to clearly understand how it
   works. HMAC can be used, without modifying any hash function, for
   calculating and verifying the message authentication values. It thus
   verifies both the data integrity and the authenticity of a message.

   The HMAC algorithm takes key K and text T as the input. The block
   size B is 64 for SHA-1, SHA-224 and SHA-256 and its 128 for SHA-384
   and SHA-512

   The Key K is the password that has been chosen and text T is the IS-
   IS PDU that needs to be authenticated.

   Because of the way the hash functions are used in HMAC construction,
   the collision attacks currently known against MD5 [MD5-attack] and
   SHA-1 [SHA-1-attack] do not apply.

5. Security Considerations

   The document proposes extensions to IS-IS which would make it more
   secure than what it is today. 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
   the PDUs which is of interest to us.

   The mechanism detailed in this document does not protect IS-IS
   against replay attacks. An adversary could in theory replay old IIHs
   and bring down the adjacency [CRYPTO] or replay old CSNPs and PSNPs
   that would cause a flood of LSPs in the network. Using some sort of
   crypto sequence numbers in IS-IS IIHs and CSNP/PSNPs is an option to
   solve this problem. Discussing this is beyond the scope of this
   document and it’s a matter which needs to be followed in the WG.

   This document states that the remaining lifetime of the LSP MUST be
   set to zero before computing the authentication, thus this field is
   not authenticated. This field is excluded so that the LSPs may be
   aged by the ISes in between without requiring to recompute the
   authentication data. This can be exploited by an attacker.

   To ensure greater security, the keys used must be changed
   periodically and implementations MUST be able to store and use more
   than one key at the same time.

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   It should be noted that the cryptographic strength of the HMAC
   depends upon the cryptographic strength of the underlying hash
   function and on the size and quality of the key.

   There are certain hash functions that require all the fields of the
   message text T to be filled with non zero values. Any extension using
   such hash functions to calculate the HMAC MUST fill the life time,
   checksum and the authentication value field of the TLV with some pre-
   defined non zero random number.

6. Acknowledgements

   We would like to thank Ran Atkinson and Tony Li for their comments
   and their earlier work on IS-IS authentication from which this draft
   has been derived.

   Thanks to Hugo Krawczyk, Arjen K. Lenstra (Bell Labs), Eric Grosse
   (Bell Labs) and Matthew J. Fanto (NIST) for educating us on some of
   the finer points related to Crypto Mathematics.

7. IANA Considerations

   IANA needs to give value for the CRYPTO_AUTH field in the
   authentication TLV 10. This document currently defines a value of 2
   to be used to denote CRYPTO_AUTH mechanism for authenticating IS-IS

8. References

8.1 Normative References

   [ISO]     "Intermediate system to Intermediate system routeing
             information exchange protocol for use in conjunction with
             the Protocol for providing the Connectionless-mode Network
             Service (ISO 8473)", ISO/IEC 10589:1992

   [RFC1195]  Callon, R., "Use of OSI IS-IS for routing in TCP/IP and
              dual environments", RFC 1195, December 1990.

   [KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119

   [RFC3567]  Li, T. and R. Atkinson, "Intermediate System to
              Intermediate System (IS-IS) Cryptographic Authentication",
              RFC 3567, July 2003

   [RFC2104]  Krawczyk, H. et al., "HMAC: Keyed-Hashing for Message
              Authentication", RFC 2104, February 1997

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   [NIST]     National Institute of Standards and Technology, "Secure
              Hash Standard", FIPS PUB 180-2, August 2002

8.2 Informative References

   [MD5-attack]   Wang, X. et al., "Collisions for Hash Functions MD4,
                  MD5, HAVAL-128 and RIPEMD", August 2004,

   [SHA-1-attack] Wang, X. et al., "Collision Search Attacks on SHA1",
                  February 2005,

   [CRYPTO]       Manral, V. et al., "Issues with existing Cryptographic
                  Protection Methods for Routing Protocols", Work in
                  Progress, February 2006

9. Author's Addresses

   Manav Bhatia
   Bangalore, India
   Email: manav@alcatel-lucent.com

   Vishwas Manral
   IP Infusion
   Almora, Uttarakhand
   Email: vishwas@ipinfusion.com

   Russ White
   Cisco Systems
   RTP North Carolina
   Email: riw@cisco.com

Full Copyright Statement

   Copyright (C) The IETF Trust (2007).

   This document is subject to the rights, licenses and restrictions
   contained in BCP 78, and except as set forth therein, the authors
   retain all their rights.

   This document and the information contained herein are provided on an

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