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Internet Draft   draft-bhatia-manral-crypto-req-isis-01.txt  March 2007


   Network Working Group                                   Manav Bhatia
   Internet Draft                                        Alcatel-Lucent
   Expires: September 2007                               Vishwas Manral
                                                            IP Infusion

       Cryptographic Algorithm Implementation Requirements for IS-IS

                draft-bhatia-manral-crypto-req-isis-01.txt

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Abstract

   IS-IS currently defines two different kinds of authentication
   schemes: Clear Text password and HMAC-MD5. There has been recently a
   new draft submitted that adds support for a generic cryptographic
   authentication scheme, which can make use of different cryptographic
   algorithms in order to authenticate the IS-IS PDUs.

   To ensure interoperability between disparate implementations, it is
   imperative that we specify a set of mandatory-to-implement algorithms
   to ensure that there is at least one algorithm that all
   implementations will have available.

   This document defines the current set of mandatory-to-implement
   algorithms to be used for the cryptographic authentication for IS-IS



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Internet Draft   draft-bhatia-manral-crypto-req-isis-01.txt  March 2007


   as well as specifying the algorithms that should be implemented
   because they may be promoted to mandatory at some future time.

Conventions used in this document

   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 [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.

   In the clear text password scheme of authentication, the passwords
   are exchanged in the clear text on the network and anyone with
   physical access to the network can learn the password and compromise
   the security of the IS-IS domain.

   The HMAC-MD5 scheme is also not good enough as there have recently
   been reports about attacks on the collision resistance properties of
   MD5 [MD5-attack]. MD5CRK, was a distributed computing project to
   break the MD5 hash algorithm in a short period of time. The project
   closed down with the publication of the paper [MD5-attack].

   It was discovered that collisions can be found in MD5 algorithm in
   less than 24 hours, making MD5 very insecure. Further research has
   verified this result and shown other ways to find collisions in MD5
   hashes. We thus need to move away from MD5 towards more complex and
   difficult to break hash algorithms.

   The [ISIS-HMAC] document recently submitted in the IETF addresses
   this. It is imperative that we move away from using MD5 to something
   thatÂ’s cryptographically more stronger (like HMAC-SHA-1).

   However, the nature of cryptography is that new algorithms surface
   continuously and existing algorithms are continuously attacked. An
   algorithm believed to be strong today may be demonstrated to be weak
   tomorrow.  Given this, the choice of mandatory-to-implement algorithm
   should be conservative so as to minimize the likelihood of it being
   compromised quickly.

   Also, we need to recognize that the mandatory-to-implement
   algorithm(s) may need to change over time to adapt to the changing
   world. For this reason, the selection of mandatory-to-implement
   algorithms should not be included in the base IS-IS specification.


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   This way it is only this document that needs to get updated, whenever
   there is a need to update the status of mandatory-to-implement
   authentication algorithms.

2. Requirements Terminology

   Keywords "MUST", "MUST NOT", "REQUIRED", "SHOULD", "SHOULD NOT" and
   "MAY" that appear in this document are to be interpreted as described
   in [RFC2119].

   We define some additional terms here:

   SHOULD+     This term means the same as SHOULD.  However, it is
               likely that an algorithm marked as SHOULD+ will be
               promoted at some future time to be a MUST.
   SHOULD-     This term means the same as SHOULD.  However, it is
               likely that an algorithm marked as SHOULD- will be
               deprecated to a MAY or worse in a future version of
               this document.
   MUST-       This term means the same as MUST.  However, we expect
               that at some point in the future this algorithm will no
               longer be a MUST.

3. Authentication Scheme Selection

   For IS-IS implementations to interoperate, they must support one or
   more authentication schemes in common. This section specifies the
   requirements for standards conformant IS-IS implementations, which
   desire to utilize the security feature.

   Old   Old         New
   Req.  RFC         Requirement  Authentication Scheme
   ---   ------      -----------  ------------------------
   MUST  ISO-10589/  SHOULD NOT   Clear Text Password (1)
         RFC 1195
   MUST  3567        MUST-        HMAC-MD5
   -     -           SHOULD+      Cryptographic Auth [ISIS-HMAC]

   The above is only true in case security is required, if there is no
   requirement of security from an implementation, the above
   requirements need not be followed

   Notes:

   (1)This is used when all the routers can "trust" one another but the
      operator does not want an accidental introduction of a router in
      the domain. This scheme of authentication is useful, but not when
      the operator wants to "cryptographically" authenticate the OSPF
      packets.


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Internet Draft   draft-bhatia-manral-crypto-req-isis-01.txt  March 2007



4. Authentication Algorithm Selection

   For IS-IS implementations to interoperate, they must support one or
   more authentication algorithms in common that can be used in the
   cryptographic scheme of authentication.

   This section details the authentication algorithm requirements for
   standards conformant IS-IS implementations.

   Old   Old         New
   Req.  RFC         Requirement  Authentication Algorithm
   ---   ------      -----------  ------------------------
   MUST  3567        MUST-        HMAC-MD5
    -     -          SHOULD+      HMAC-SHA-1 [ISIS-HMAC]
    -     -          MAY+         HMAC-SHA-256/HMAC-SHA-384/HMAC-SHA-512


5. Security Considerations

   The cryptographic mechanisms defined in this document define only
   authentication algorithms, and do not provide any confidentiality.
   However encrypting the content of the packet (providing
   confidentiality) is not of as great a value to routing protocols as
   authenticating the source of the packet.

   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.

   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.

   This document concerns itself with the selection of cryptographic
   algorithms for the use of IS-IS, specifically with the selection of
   "mandatory-to-implement" algorithms.  The algorithms identified in
   this document as "MUST implement" or "SHOULD implement" are not known
   to be broken at the current time, and cryptographic research so far
   leads us to believe that they will likely remain secure into the
   foreseeable future.  However, this isn't necessarily forever.  We
   would therefore expect that new revisions of this document will be
   issued from time to time that reflect the current best practice in
   this area.

6. Acknowledgements





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   Much of the wording herein was adapted from RFC 4307, "Cryptographic
   Algorithms for Use in the Internet Key Exchange Version 2", by
   Jeffrey I. Schiller.

7. IANA Considerations

   This document places no requests to IANA.

8. References

8.1 Normative References

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

   [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.

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

   [ISIS-HMAC] Bhatia, M., Manral, V. and White, R.,"ISIS HMAC
               Cryptographic Authentication", Work in Progress

8.2 Informative References

   [MD5-attack]   Wang, X. et al., "Collisions for Hash Functions MD4,
                  MD5, HAVAL-128 and RIPEMD", August 2004,
                  http://eprint.iacr.org/2004/199

9. Author's Addresses

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

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



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