Network Working Group                                    M. Jethanandani
Internet-Draft                                             Cisco Systems
Intended status: Standards Track                               A. Mishra
Expires: July 9, December 29, 2017                                  O3b Networks
                                                               A. Saxena
                                                       Ciena Corporation
                                                               M. Bhatia
                                                          Ionos Networks
                                                         January 5,
                                                           June 27, 2017

                     Optimizing BFD Authentication


   This document describes an optimization to BFD Authentication as
   described in Section 6.7 of BFD [RFC5880].

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
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   This Internet-Draft will expire on July 9, December 29, 2017.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Authentication Mode . . . . . . . . . . . . . . . . . . . . .   3
   3.  NULL Auth TLV . . . . . . . . . . . . . . . . . . . . . . . .   4
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .   5
     6.2.  Informative References  . . . . . . . . . . . . . . . . .   6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   7   8

1.  Introduction

   Authenticating every BFD [RFC5880] packet with a Simple Password, or
   with a MD5 Message-Digest Algorithm [RFC1321] , or Secure Hash
   Algorithm (SHA-1) algorithms is computationally intensive process,
   making it difficult if not impossible to authenticate every packet -
   particularly at faster rates.  Also, 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 [RFC6194].  If replaced by stronger
   algorithms, the computational overhead, will make the task of
   authenticating every packet even more difficult to achieve.

   This document proposes that only BFD frames that signal a state
   change in BFD be authenticated.  Rest of the frames can be
   transmitted and received without authentication enabled.  Most frames
   that are transmitted and received have no state change associated
   with them.  Limiting authentication to frames that affect a BFD
   session state allows more sessions to be supported for
   authentication.  Moreover, most BFD frames that signal a state change
   are generally transmitted at a slower interval of 1s leaving enough
   time to compute the hash.

   Section 2 talks about the changes to authentication mode as described
   in BFD [RFC5880].

2.  Authentication Mode

   The cryptographic authentication mechanisms specified in BFD
   [RFC5880] describes enabling and disabling of authentication as a one
   time operation.  As a security precaution, it mentions that
   authentication state be allowed to change at most once.  Once
   enabled, every packet must have Authentication Bit set and the
   associated Authentication TLV appended.  In addition, it states that
   an implementation SHOULD NOT allow the authentication state to be
   changed based on the receipt of a BFD Control packet.

   This document proposes that the authentication mode be modified to be
   enabled on demand.  Instead of authenticating every packet, BFD peers
   decide which frames need to be authenticated, and authenticate only
   those frames.  For example, the two ends can decide that BFD frames
   that indicate a state change should be authenticated and enable
   authentication on those frames only.  If the two ends have not
   previously negotiated which frames they will transmit or receive with
   authentication enabled, then the BFD session will fail to come up,
   because at least one end will expect every frame to be authenticated.
   The state changes for which authentication is being suggested

          Read   : On state change from <column> to <row>
          Auth   : Authenticate frame
          NULL   : No Authentication. Use NULL AUTH TLV.
          n/a    : Invalid state transition.
          Select : Most frames NULL AUTH. Selective (periodic)
                   frames authenticated.
         |        | DOWN   | INIT   | UP     | POLL   | DEMAND |
         | DOWN   |  NULL  |  Auth  |  Auth  |  Auth  |  Auth  |
         | INIT   |  Auth  |  NULL  |  Auth  |  Auth  |  Auth  |
         | UP     |  Auth  |  n/a   | Select |  Auth  |  Auth  |
         | POLL   |  Auth  |  n/a   |  Auth  |  Auth  |  Auth  |
         | DEMAND |  Auth  |  Auth  |  Auth  |  Auth  |  Auth  |

                       Optimized Authentication Map

   All frames already carry the sequence number.  The NULL AUTH frames
   MUST contain the TLV specified in Section 3.  This enables a
   monotonically increasing sequence number to be carried in each frame,
   and prevents man-in-the-middle from capturing and replaying the same
   frame again.  Since all frames still carry a sequence number, the
   logic for sequence number maintenance remains unchanged from
   [RFC5880].  If at a later time, a different scheme is adopted for
   changing sequence number, this method can use the updated scheme
   without any impact.

   Most frames transmitted on a BFD session are BFD CC UP frames.
   Authenticating a small subset of these frames (one per configured
   period) significantly reduces the computational demand for the system
   while maintaining security of the session across the configured
   authentication periods.  The configuration of the periodic
   authentication interval for BFD CC UP frames is an open issue.

3.  NULL Auth TLV

   This section describes a new Authentication TLV as:

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       |   Auth Type   |   Auth Len    |  Auth Key ID  |   Reserved    |
       |                        Sequence Number                        |

                               NULL Auth TLV


   Auth Type: The Authentication Type, which in this case is 0 (NULL
   Auth TL)

   Auth Len: The length of the NULL Auth TLV, in bytes i.e. 8 bytes

   Auth Key ID: The authentication key ID in use for this packet.  Must
   be set to zero.

   Reserved: The authentication key ID in use for this packet.  This
   allows multiple keys to be active simultaneously.

   Sequence Number: The sequence number for this packet.  This value is
   incremented for each successive packet transmitted for a session.
   This provides protection against replay attacks.  Must  Implementation
   may use the same sequence number counter numbers as the authenticated frames. defined in [RFC5880], or secure sequence
   numbers as defined in [I-D.ietf-bfd-secure-sequence-numbers].

   The NULL Auth TLV must be used for all frames that are not
   authenticated.  This protects against replay-attacks by allowing the
   session to maintain an incrementing sequence number for all frames
   (authenticated and un-authenticated).

   In the future, if a new scheme is adopted for changing the sequence
   number, this method can adopt the new scheme without any impact.

4.  IANA Considerations

   This document requests an update to the registry titled "BFD
   Authentication Types".  IANA is requested to update the Value of 0
   which is currently named as Reserved to NULL (see Section 3).

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

5.  Security Considerations

   The approach described in this document enhances the ability to
   authentication a BFD session by taking away the onerous requirement
   that every frame be authenticated.  By authenticating frames that
   affect the state of the session, the security of the BFD session is
   maintained.  As such this document does not change the security
   considerations for BFD.

6.  References

6.1.  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.

              Mishra, A., Jethanandani, M., Saxena, A., Networks, J.,
              Chen, M., and P. Fan, "BFD Stability", draft-ashesh-bfd-
              stability-04 (work in progress), March 2016.

              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.

              Jethanandani, M., Agarwal, S., Mishra, A., Saxena, A., and
              A. DeKok, "Secure BFD Sequence Numbers", draft-ietf-bfd-
              secure-sequence-numbers-00 (work in progress), May 2017.

              Mishra, A., Jethanandani, M., Saxena, A., Networks, J.,
              Chen, M., and P. Fan, "BFD Stability", draft-ietf-bfd-
              stability-00 (work in progress), May 2017.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

   [RFC6039]  Manral, V., Bhatia, M., Jaeggli, J., and R. White, "Issues
              with Existing Cryptographic Protection Methods for Routing
              Protocols", RFC 6039, DOI 10.17487/RFC6039, October 2010,

   [RFC6151]  Turner, S. and L. Chen, "Updated Security Considerations
              for the MD5 Message-Digest and the HMAC-MD5 Algorithms",
              RFC 6151, DOI 10.17487/RFC6151, 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, DOI 10.17487/RFC6194, March 2011,

6.2.  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

              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,
              DOI 10.17487/RFC1321, April 1992,

   [RFC2104]  Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-
              Hashing for Message Authentication", RFC 2104,
              DOI 10.17487/RFC2104, February 1997,

   [RFC4086]  Eastlake 3rd, D., Schiller, J., and S. Crocker,
              "Randomness Requirements for Security", BCP 106, RFC 4086,
              DOI 10.17487/RFC4086, June 2005,

   [RFC4822]  Atkinson, R. and M. Fanto, "RIPv2 Cryptographic
              Authentication", RFC 4822, DOI 10.17487/RFC4822, February
              2007, <>.

   [RFC5310]  Bhatia, M., Manral, V., Li, T., Atkinson, R., White, R.,
              and M. Fanto, "IS-IS Generic Cryptographic
              Authentication", RFC 5310, DOI 10.17487/RFC5310, 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, DOI 10.17487/RFC5709, October
              2009, <>.

   [RFC5880]  Katz, D. and D. Ward, "Bidirectional Forwarding Detection
              (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010,

   [RFC6234]  Eastlake 3rd, D. and T. Hansen, "US Secure Hash Algorithms
              (SHA and SHA-based HMAC and HKDF)", RFC 6234,
              DOI 10.17487/RFC6234, 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

   Mahesh Jethanandani
   Cisco Systems
   170 W. Tasman Drive
   San Jose, CA  95134

   Phone: +1 (408) 526-8763

   Ashesh Mishra
   Ciena Corporation
   3939 North 1st Street
   San Jose, CA  95134
   O3b Networks


   Ankur Saxena
   Ciena Corporation
   3939 N 1st Street
   San Jose, CA  95134


   Manav Bhatia
   Ionos Networks