Network Working Group                                           D. Zhang
Internet-Draft                                                    Huawei
Intended status: Standards Track                               M. Bhatia
Expires: November 25, 2014                                Alcatel-Lucent
                                                               V. Manral
                                                          Ionos Networks
                                                         M. Jethanandani
                                                       Ciena Corporation
                                                            May 24, 2014

             Authenticating BFD using HMAC-SHA-2 procedures


   This document describes the mechanism to authenticate Bidirectional
   Forwarding Detection (BFD) protocol packets using Hashed Message
   Authentication Mode (HMAC) with the SHA-256, SHA-384, and SHA-512
   algorithms.  The described mechanism uses the Generic Cryptographic
   Authentication and Generic Meticulous Cryptographic Authentication
   sections to carry the authentication data.  This document updates,
   but does not supersede, the cryptographic authentication mechanism
   specified in RFC 5880.

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [RFC2119].

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on November 25, 2014.

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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
   ( 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  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Cryptographic Aspects . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Preperation of the Key  . . . . . . . . . . . . . . . . .   4
     2.2.  First Hash  . . . . . . . . . . . . . . . . . . . . . . .   4
     2.3.  Second Hash T . . . . . . . . . . . . . . . . . . . . . .   4
     2.4.  Result  . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   5.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     5.1.  Normative References  . . . . . . . . . . . . . . . . . .   5
     5.2.  Informative References  . . . . . . . . . . . . . . . . .   6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   The cryptographic authentication mechanisms specified in BFD
   [RFC5880] defines MD5 Message-Digest Algorithm [RFC1321] and Secure
   Hash Algorithm (SHA-1) algorithms to authenticate BFD packets.  The
   recent escalating series of attacks on MD5 and SHA-1 [SHA-1-attack1]
   [SHA-1-attack2] raise concerns about their remaining useful lifetime
   as outlined in Updated Security Considerations for the MD5 Message-
   Digest and the HMAC-MD5 Algorithm [RFC6151] and Security
   Considerations for the SHA-0 and SHA-1 Message-Digest Algorithm

   These attacks may not necessarily result in direct vulnerabilities
   for Keyed-MD5 and Keyed-SHA-1 digests as message authentication codes
   because the colliding message may not correspond to a syntactically
   correct BFD protocol packet.  Regardless, there is a need felt to
   deprecate MD5 and SHA-1 as the basis for the HMAC algorithm in favor
   of stronger digest algorithms.

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   This document adds support for Secure Hash Algorithms (SHA) defined
   in the US NIST Secure Hash Standard (SHS), which is defined by NIST
   FIPS 180-2 [FIPS-180-2].  [FIPS-180-2] includes SHA-1, SHA-224,
   SHA-256, SHA-384, and SHA-512.  The HMAC authentication mode defined
   in NIST FIPS 198 is used [FIPS-198].

   It is believed that the HMAC algorithms defined in HMAC: Keyed-
   Hashing for Message Authentication [RFC2104] is mathematically
   identical to their counterparts in [FIPS-198] and it is also believed
   that algorithms in US Secure Hash Algorithms [RFC6234] are
   mathematically identical to those defined in [FIPS-180-2].

   It should be noted that the collision attacks currently known against
   SHA-1 do not apply when SHA-1 is used in the HMAC construction.  NIST
   will be supporting HMAC-SHA-1 even after 2010 [NIST-HMAC-SHA] ,
   whereas it would be dropping support for SHA-1 in digital signatures.

   BFD Generic Cryptographic Authentication
   [I-D.ietf-bfd-generic-crypto-auth] defines new authentication types -
   Generic Cryptographic Authentication (TBD1) and Generic Meticulous
   Cryptographic Authentication (TBD2) that can be used for carrying the
   authentication digests defined in this document.  Also please refer
   to this document for the procedures at the sending and the receiving

   Implementations of this specification must include support for at
   least HMAC-SHA-256 and may include support for either of HMAC-SHA-384
   or HMAC-SHA-512.

2.  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 BFD packet.

   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 is equal to 64.  For SHA-384 and SHA-512 B is equal to 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.

2.1.  Preperation 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.

2.2.  First Hash

   First, the Authentication Data field in the Generic Authentication
   Section is filled with the value of Apad and the Authentication Type
   field is set to TBD1 or TBD2 depending upon which Authentication Type
   being used.  The Sequence Number field MUST be set to

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

   First-Hash = H(Ko XOR Ipad || (BFD Packet))

2.3.  Second Hash T

   Then a second hash, also known as the outer hash, is computed as

   Second-Hash = H(Ko XOR Opad || First-Hash)

2.4.  Result

   The resultant Second-Hash becomes the Authentication Data that is
   sent in the Authentication Data field of the BFD Authentication
   Section.  The length of the Authentication Data field 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 BFD Packet as transmitted on the

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3.  IANA Considerations

   This document makes no request of IANA.

   Note to RFC Editor: this section may be removed on publication as an

4.  Security Considerations

   The approach described in this document enhances the security of the
   BFD protocol by adding, to the existing BFD cryptographic
   authentication methods, support for the SHA-2 algorithms defined in
   the NIST Secure Hash Standard (SHS) using the HMAC mode.  However,
   the confidentiality protection for BFD packets is out of scope of
   this work .

   Because all of the currently specified algorithms use symmetric
   cryptography, one cannot authenticate precisely which BFD device sent
   a given packet.  However, one can authenticate that the sender knew
   the BFD Security Association (including the BFD SA's parameters)
   currently in use.

   To enhance system security, the applied keys should be changed
   periodically and implementations SHOULD be able to store and use more
   than one key at the same time.  The quality of the security provided
   by the cryptographic authentication option depends completely on the
   strength of the cryptographic algorithm and cryptographic mode in
   use, the strength of the key being used, and the correct
   implementation of the security mechanism in all communicating BFD
   implementations.  Accordingly, the use of high assurance development
   methods is recommended.  It also requires that all parties maintain
   the secrecy of the shared secret key.  Randomness Requirements for
   Security [RFC4086] provides guidance on methods for generating
   cryptographically random bits.

   The value Apad is used here primarily for consistency with IETF
   specifications for HMAC-SHA authentication for RIPv2 RIPv2
   Cryptographic Authentication [RFC4822], IS-IS IS-IS Generic
   Cryptographic Authentication [RFC5310] and OSPFv2 OSPFv2 HMAC-SHA
   Cryptographic Authentication [RFC5709].

5.  References

5.1.  Normative References

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              National Institute of Standards and Technology, FIPS PUB
              180-2, "The Keyed-Hash Message Authentication Code
              (HMAC)", August 2002.

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

              Bhatia, M., Manral, V., Zhang, D., and M. Jethanandani,
              "BFD Generic Cryptographic Authentication", draft-ietf-
              bfd-generic-crypto-auth-06 (work in progress), April 2014.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC6039]  Manral, V., Bhatia, M., Jaeggli, J., and R. White, "Issues
              with Existing Cryptographic Protection Methods for Routing
              Protocols", RFC 6039, October 2010.

   [RFC6151]  Turner, S. and L. Chen, "Updated Security Considerations
              for the MD5 Message-Digest and the HMAC-MD5 Algorithms",
              RFC 6151, March 2011.

   [RFC6194]  Polk, T., Chen, L., Turner, S., and P. Hoffman, "Security
              Considerations for the SHA-0 and SHA-1 Message-Digest
              Algorithms", RFC 6194, March 2011.

5.2.  Informative References

   [Dobb96a]  Dobbertin, H., "Cryptanalysis of MD5 Compress", May 1996.

   [Dobb96b]  Dobbertin, H., "The Status of MD5 After a Recent Attack",
              CryptoBytes", 1996.

              Lebovitz, G. and M. Bhatia, "Keying and Authentication for
              Routing Protocols (KARP) Design Guidelines", draft-ietf-
              karp-design-guide-10 (work in progress), December 2011.

              Wang, X., Feng, D., Lai, X., and H. Yu, "Collisions for
              Hash Functions MD4, MD5, HAVAL-128 and RIPEMD", August

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              National Institute of Standards and Technology, Available
              online at,
              "NIST's Policy on Hash Functions", 2006.

   [RFC1321]  Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321,
              April 1992.

   [RFC2104]  Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-
              Hashing for Message Authentication", RFC 2104, February

   [RFC4086]  Eastlake, D., Schiller, J., and S. Crocker, "Randomness
              Requirements for Security", BCP 106, RFC 4086, June 2005.

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

   [RFC5310]  Bhatia, M., Manral, V., Li, T., Atkinson, R., White, R.,
              and M. Fanto, "IS-IS Generic Cryptographic
              Authentication", RFC 5310, February 2009.

   [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.

   [RFC5880]  Katz, D. and D. Ward, "Bidirectional Forwarding Detection
              (BFD)", RFC 5880, June 2010.

   [RFC6234]  Eastlake, D. and T. Hansen, "US Secure Hash Algorithms
              (SHA and SHA-based HMAC and HKDF)", RFC 6234, May 2011.

              Wang, X., Yin, Y., and H. Yu, "Finding Collisions in the
              Full SHA-1", 2005.

              Wang, X., Yao, A., and F. Yao, "New Collision Search for
              SHA-1", 2005.

Authors' Addresses

   Dacheng Zhang


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   Manav Bhatia
   Bangalore  560045


   Vishwas Manral
   Ionos Networks


   Mahesh Jethanandani
   Ciena Corporation
   3939 North 1st Street
   San Jose, CA  95134

   Phone: +1 (408) 904-2160

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