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Versions: 00 01 02 03 04 05 06 07 rfc5310                Standards Track
Internet Draft IS-IS Generic Cryptographic Authentication November 2009

   Network Working Group                                   Manav Bhatia
   Internet Draft                                        Alcatel-Lucent
   Intended Status: Proposed Standard                    Vishwas Manral
   Expires: April 2009                                      IP Infusion
                                                                Tony Li
                                                  Redback Networks Inc.
                                                    Randall J. Atkinson
                                                       Extreme Networks
                                                             Russ White
                                                          Cisco Systems
                                                       Matthew J. Fanto
                                                             Ciber Inc.

                IS-IS Generic Cryptographic Authentication


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   This document proposes an extension to Intermediate System to
   Intermediate System (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
   5304. IS-IS is specified in International Standards Organization

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   (ISO) 10589, with extensions to support Internet Protocol version 4
   (IPv4) described in RFC 1195.

   Although this document has been written specifically for using the
   Hashed Message Authentication Code (HMAC) construct along with the
   Secure Hash Algorithm (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

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. [RFC2119]


   1. Introduction...................................................2
   2. IS-IS Security Association.....................................3
   3. Authentication Procedures......................................4
      3.1 Authentication TLV.........................................4
      3.2 Authentication Process.....................................5
      3.3 Cryptographic Aspects......................................5
      3.4 Procedures at the Sending Side.............................6
      3.5 Procedure at the Receiving Side............................7
   4. Security Considerations........................................8
   5. Acknowledgements...............................................9
   6. IANA Considerations............................................9
   7. References.....................................................9
      7.1 Normative References.......................................9
      7.2 Informative References....................................10
   8. Author's Addresses............................................10

1. Introduction

   Intermediate System to Intermediate System (IS-IS) specification
   [ISO] [RFC1195] allows for authentication of its Protocol Data Units
   (PDUs) via the authentication TLV 10 that is carried as a part of the
   PDU. The base specification has provision for only clear text
   passwords and RFC 5304 [RFC5304] augments this to provide the
   capability to use Hashed Message Authentication Code - Message Digest
   5 (HMAC-MD5) authentication for its PDUs.

   The first octet of the 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

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   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 generic 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 [FIPS-180-3] 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 (SA).

   While at the time of this writing there are no openly published
   attacks on the HMAC-MD5 mechanism, some reports [Dobb96a, Dobb96b]
   create concern about the ultimate strength of the MD5 cryptographic
   hash function.

   The mechanism described in this document does not provide
   confidentiality, since PDUs are sent in the clear.  However, the
   objective of a routing protocol is to advertise the routing topology,
   and confidentiality is not normally required for routing protocols.

2. IS-IS Security Association

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

   Parameters associated with an IS-IS SA:

   O Key Identifier (Key ID) : This is a two 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 the Key ID field
   in the incoming PDU.

   The sender based on the active configuration, selects the Security
   Association to use and puts the correct Key ID value associated with
   the Security Association in the IS-IS PDU. If multiple valid and
   active IS-IS Security Associations exist for a given outbound
   interface at the time an IS-IS PDU is sent, the sender may use any of
   those security associations to protect the packet.

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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 an 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. This information is never
   sent in cleartext over the wire. Because this information is not sent
   on the wire, the implementer chooses an implementation specific
   representation for this information. At present, the following values
   are possible: HMAC-SHA-1, HMAC-SHA-224, HMAC-SHA-256, HMAC-SHA-384
   and HMAC-SHA-512.

   o Authentication Key : This value denotes the cryptographic
   authentication 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, 3, 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 (10).

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                   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 Authentication Process

   When calculating the CRYPTO_AUTH result for Sequence Number PDUs,
   Level 1 Sequence Number PDUs SHALL use the Area Authentication string
   as in Level 1 Link State PDUs. Level 2 Sequence Number PDUs shall use
   the domain authentication string as in Level 2 Link State PDUs.

   IS-IS HELLO PDUs SHALL use the Link Level Authentication String,
   which MAY be different from that of Link State PDUs. The CRYPTO_AUTH
   result for the IS-IS HELLO PDUs SHALL be calculated after the PDU is
   padded to the MTU size, if padding is not disabled.  Implementations
   that support the optional checksum for the Sequence Number PDUs and
   IS-IS HELLO PDUs MUST NOT include the Checksum TLV.

3.3 Cryptographic Aspects

   In the algorithm description below, the following nomenclature, which
   is consistent with [FIPS-198], is used:

   H    is the specific hashing algorithm (e.g. SHA-256).
   K    is the password for the PDU type as per the International
        Standard ISO/IEC 10589 [ISO].
   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.

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   Opad is the hexadecimal value 0x5c repeated B times.
   Ipad is the hexadecimal value 0x36 repeated B times.
   Apad is the hexadecimal value 0x878FE1F3 repeated (L/4) times.

   (1)Preparation of the Key

      In this application, Ko is always L octets long.

      If the Authentication Key (K) is L octets long, then Ko is equal
      to K.  If the Authentication Key (K) is more than L octets long,
      then Ko is set to H(K).  If the Authentication Key (K) is less
      than L octets long, then Ko is set to the Authentication Key (K)
      with zeros appended to the end of the Authentication Key (K) such
      that Ko is L octets long.

   (2)First Hash

      First, the IS-IS packet's Authentication Data field is filled with
      the value Apad and the Authentication Type field is set to 0x3.

      Then, a first hash, also known as the inner hash, is computed
      as follows:

              First-Hash = H(Ko XOR Ipad || (IS-IS PDU))

   (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)


      The result Second-Hash becomes the Authentication Data that is
      sent in the Authentication Data field of the IS-IS PDU. The length
      of the Authentication Data field is always identical to the
      message digest size of the specific hash function H that is being

      This also means that the use of hash functions with larger output
      sizes will also increase the size of the IS-IS PDU as transmitted
      on the wire.

3.4 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 authentication data
   is computed as explained in the previous section. The length of the
   TLV is set as per the authentication algorithm that is being used.

   The length is set to 23 for HMAC-SHA-1, 31 for HMAC-SHA-224, 35 for
   HMAC-SHA-256, 51 for HMAC-SHA-384 and 67 for HMAC-SHA-512. Note that
   two octets have been added to account for the Key ID and one octet
   for the authentication type.

   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

3.5 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.

   It should then set the Authentication Value field with Apad and zero
   the Checksum and Remaining Life time fields before 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

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   process of migrating to the new CRYPTO_AUTH based authentication

4. 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.

   It should be noted that authentication method described in this
   document is not being used to authenticate the specific originator of
   a PDU, but is rather being used to confirm that the PDU has indeed
   been issued by an intermediate system which had access to the area or
   the domain password, depending upon the kind of PDU it is.

   The mechanism described here is not perfect and does not need to be
   perfect. Instead, this mechanism represents a significant increase in
   the work function of an adversary attacking the IS-IS
   protocol, while not causing undue implementation, deployment, or
   operational complexity.

   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

   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.

   There is a transition mode suggested where routers can ignore the
   CRYPTO_AUTH information carried in the PDUs. The operator must ensure
   that this mode is only used when migrating to the new CRYPTO_AUTH
   based authentication scheme as this leaves the router vulnerable to
   an attack.

   To ensure greater security, the keys used should be changed
   periodically and implementations MUST be able to store and use more
   than one key at the same time. Operators should ensure that the
   authentication key is never sent over the network in clear-text via
   any protocol. Care should also be taken to ensure that the selected
   key is unpredictable, avoiding any keys known to be weak for the

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   algorithm in use. [RFC4086] contains helpful information on both key
   generation techniques and cryptographic randomness.

   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.

   If a stronger authentication were believed to be required, then the
   use of a full digital signature [RFC2154] would be an approach that
   should be seriously considered.  It was rejected for this purpose at
   this time because the computational burden of full digital signatures
   is believed to be much higher than is reasonable given the current
   threat environment in operational commercial networks.

5. Acknowledgements

   The authors would like to thank Hugo Krawczyk, Arjen K. Lenstra (Bell
   Labs) and Eric Grosse (Bell Labs) for educating us on some of the
   finer points related to Crypto Mathematics.

   We would also like to thank Bill Burr, Tim Polk, John Kelsey, and
   Morris Dworkin of (US) NIST for review of portions of this document
   that are directly derived from the closely related work on RIPv2
   Cryptographic Authentication [RFC-4822].

   We would also like to mention Alfred Hoenes for his careful and
   detailed review during the last call.

6. IANA Considerations

   Upon publication of this RFC, IANA shall register the pre-allocated
   value for the CRYPTO_AUTH method in the "IS-IS Authentication Type
   Codes for TLV 10" subregistry established by [RFC5304].

   This document currently defines the value 3 to be used to denote the
   CRYPTO_AUTH mechanism for authenticating IS-IS PDUs.

   | Authentication Type Code                   | Value | Reference   |
   | Cryptographic Authentication (CRYPTO_AUTH) |   3   |  RFC {this} |

7. References

7.1 Normative References

   [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119

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   [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.

   [RFC5304]  Li, T. and Atkinson, R. "Intermediate System to
              Intermediate System (IS-IS) Cryptographic Authentication",
              RFC 5304, October 2008.

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

   [FIPS-180-3] National Institute of Standards and Technology, "Secure
              Hash Standard (SHS)", FIPS PUB 180-3, October 2008

   [FIPS-198] US National Institute of Standards & Technology, "The
              Keyed-Hash Message Authentication Code (HMAC)", FIPS PUB
              198, March 2002.

7.2 Informative References

   [Dobb96a]  Dobbertin, H, "Cryptanalysis of MD5 Compress", Technical
              Report, 2 May 1996. (Presented at the Rump Session of
              EuroCrypt 1996.)

   [Dobb96b]  Dobbertin, H, "The Status of MD5 After a Recent Attack",
              CryptoBytes, Vol. 2, No. 2, Summer 1996.

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

   [RFC2154] S. Murphy, M. Badger, and B. Wellington, "OSPF with
              Digital Signatures", RFC 2154, June 1997.

   [RFC4822] R. Atkinson, M. Fanto, "RIPv2 Cryptographic
              Authentication", RFC 4822, February 2007.

8. Author's Addresses

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

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   Tony Li
   Redback Networks Inc.
   300 Holger Way
   San Jose CA 95134
   EMail: tony.li@tony.li

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

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

   Randall J. Atkinson
   Extreme Networks
   3585 Monroe Street
   Santa Clara, CA 95051
   Email: rja@extremenetworks.com

   Matthew J. Fanto
   Ciber Inc.
   Dearborn, Mi
   Email: mfanto@ciber.com

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