Network Working Group                                           D. Zhang
Internet-Draft                                                    Huawei
Intended status: Standards Track                              M. Bhatia
Expires: January 4, April 22, 2013                                   Alcatel-Lucent
                                                              V. Manral
                                                     Hewlett-Packard Co.
                                                           July 03,
                                                        October 19, 2012

             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 mechanism described mechanism uses the Generic Cryptographic
   Authentication and Generic Meticulous Cryptographic Authentication
   sections to carry the authentication data.  This document updates,
   but does not supercede, 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.

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   This Internet-Draft will expire on January 4, April 22, 2013.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Cryptographic Aspects . . . . . . . . . . . . . . . . . . . . . 3
   3.  Procedures at the Sending Side  . . . . . . . . . . . . . . . . 5
   4.  Procedure at the Receiving Side . . . . . . . . . . . . . . . . 5
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
   6.  Security Considerations . . . . . . . . . . . . . . . . . . . . 6 7
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 7
     7.1.  Normative References  . . . . . . . . . . . . . . . . . . . 7
     7.2.  Informative References  . . . . . . . . . . . . . . . . . . 8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 9

1.  Introduction

   The cryptographic authentication mechanisms specified in BFD [RFC5880]
   defines MD5 [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 [RFC6151] [RFC6194].

   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.

   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 [RFC2104] is
   mathematically identical to their counterparts in [FIPS-198] and it
   is also believed that algorithms in [RFC6234] are mathematically
   identical to those defined in [FIPS-180-2].

   It should be noted that if SHA-1 is used in the HMAC construction
   then collision attacks currently known against
   SHA-1 do not apply.
   The new attacks on apply when SHA-1 have no impact on is used in the security of
   HMAC-SHA-1. 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.

   [I-D.ietf-bfd-generic-crypto-auth] defines new authentication types -
   Generic Cryptographic Authentication and Generic Meticulous
   Cryptographic Authenticationan extension Authentication that can be used for carrying the
   authentication digests defined in this document.

   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 == 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 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 Authentication Data field in the Generic Authentication
   Section is filled with the value of Apad and the Authentication Type
   field is set to 6 or 7 depending upon which Authentication Type is
   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))

   (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)
   (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

3.  Procedures at the Sending Side

   Before a BFD device sends a BFD packet out, the device needs to
   select an appropriate BFD SA from its local key table if a keyed
   digest for the packet is required.  If no appropriate SA is
   avaliable, the BFD packet MUST be discarded.

   If an appropriate SA is avaliable, the device then derives the key
   and the associated authentication algorithm (HMAC-SHA-256, HMAC-SHA-
   384 or HMAC-SHA-512) from the SA.

   The device then start performing the operations illustrated in
   Section 2.  Before the authentication data is computed, the device
   MUST fill the Auth Type field and the Auth length . field.  The
   Sequence Number field MUST be set to bfd.XmitAuthSeq.

   The value of Auth Length in the generic authentication section is
   various according to different authentication algorithms being used.
   Specifically, the value is 40 for HMAC-SHA-256, 56 for HMAC-SHA-384 HMAC-SHA-384,
   and 72 for HMAC- SHA-512.

   The Key ID is then filled.

   After that, the authentication data is computed as illustrated in
   Section 3. 2.

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

4.  Procedure at the Receiving Side

   Upon receiving a BFD packet with an generic authentication section
   appended, the receiving a device needs to find an appropriate BFD SA from its local
   key table to verify the packet.  The SA is located by the Key ID in
   the authentication section of the packet.

   If there is no SA is associated with the Key ID, the received packet
   MUST be discarded.

   If bfd.AuthSeqKnown is 1, examine the Sequence Number field. field is examined.  For
   Cryptographic Authentication, if the Sequence Number lies outside of
   the range of bfd.RcvAuthSeq to bfd.RcvAuthSeq+(3*Detect Mult)
   inclusive (when treated as an unsigned 32 bit circular number space),
   the received packet MUST be discarded.  For Meticulous Cryptographic
   Authentication, if the Sequence Number lies outside of the range of
   bfd.RcvAuthSeq+1 to bfd.RcvAuthSeq+(3*Detect Mult) inclusive (when
   treated as an unsigned 32 bit circular number space, the received
   packet MUST be discarded.


   An authentication Algorithm dependent processing, process then needs to be performed,
   performed by using the algorithm specified by the appropriate BFD SA
   for the received packet.

   Before the device performs any processing, it needs to save the
   content of the Authentication Value field.

   The device then needs to field and set the Authentication
   Value field with Apad
   before Apad.

   The device then computes the authentication data is computed. as illustrated in
   Section 2.  The calculated data is compared with the received
   authentication data in the packet.

   The packet MUST be discarded if the calculated data and the received
   authentication data do not match each other. match.  In such a this case, an error event
   SHOULD be logged.

   A BFD implementation MAY be in a transition mode where it includes
   CRYPTO_AUTH or the MET_CRYPTO_AUTH information in packets but never
   verifies it.  This is provided as a transition aid for networks in
   the process of migrating to the new CRYPTO_AUTH and MET_CRYPTO_AUTH
   based authentication schemes.

5.  IANA Considerations

   This document makes no request of IANA.

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

6.  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.  [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 [RFC4822], IS-IS
   [RFC5310] and OSPFv2 [RFC5709].

7.  References

7.1.  Normative References

              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., and D. Zhang, "BFD Generic
              Cryptographic Authentication",
              draft-ietf-bfd-generic-crypto-auth-02 (work in progress),
              June 2012.

   [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.

7.2.  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 2004.

              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 1997.

   [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


   Manav Bhatia
   Bangalore  560045

   Vishwas Manral
   Hewlett-Packard Co.
   19111 Pruneridge Ave.
   Cupertino, CA  95014