Network Working Group                                    M. Jethanandani
Internet-Draft                                                    VMware
Intended status: Standards Track                               A. Mishra
Expires: May 15, 2019                                       SES Networks
                                                               A. Saxena
                                                       Ciena Corporation
                                                               M. Bhatia
                                                       November 11, 2018

                     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 BCP 14 [RFC2119]
   [RFC8174] when, and only when, they appear in all capitals, as shown

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 May 15, 2019.

Jethanandani, et al.      Expires May 15, 2019                  [Page 1]

Internet-Draft       BFD Authentication Optimization       November 2018

Copyright Notice

   Copyright (c) 2018 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.  Authentication Mode . . . . . . . . . . . . . . . . . . . . .   3
   3.  NULL Auth TLV . . . . . . . . . . . . . . . . . . . . . . . .   4
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
     6.2.  Informative References  . . . . . . . . . . . . . . . . .   6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   7

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

Jethanandani, et al.      Expires May 15, 2019                  [Page 2]

Internet-Draft       BFD Authentication Optimization       November 2018

   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.  To detect a Man In the Middle (MITM)
   attack, it is also proposed that a non-state change frame be
   authenticated occasionally.  The interval of this non-state change
   frame can be configured depending on the detect multiplier and the
   capability of the system.  As an example, this could be equal to the
   detect multiplier number of packets.

   The rest of the document is structured as follows.  Section 2 talks
   about the changes to authentication mode as described in BFD
   [RFC5880].  Section 3 goes into the details of the new Authentication

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
   are configured for which frames need to be authenticated, and
   authenticate only those frames.  Rest of the frames can be
   transmitted and received without authentication.  For example, the
   two ends can be configured such that BFD frames that indicate a state
   change should be authenticated and enable authentication on those
   frames only.  If the two ends have previously been configured as
   such, but at least one side decides not to authenticate a state
   change frame, then the BFD session will fail to come up.

   This proposal outlines which frames need to be authenticated (carry
   the A-bit), and which frames can be transmitted or received without
   authentication enabled.  A frame that fails authentication is
   discarded, or a frame that was supposed to be authenticated, but was
   not, e.g. a state-change frame, is discarded.  However, there is no
   change to the state machine for BFD, as the decision of a state
   change is still decided by how many valid consecutive frames were
   received, authenticated or otherwise.

   The state changes for which authentication is being suggested

Jethanandani, et al.      Expires May 15, 2019                  [Page 3]

Internet-Draft       BFD Authentication Optimization       November 2018

          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, for example, a detect
   multiplier number of packets per configured period, significantly
   reduces the computational demand for the system while maintaining
   security of the session across the configured authentication periods.
   A minimum of Detect Multiplier packets MUST be transmitted per
   configured periodic authentication interval.  This ensures that the
   BFD session should see at least one authenticated packet during that

3.  NULL Auth TLV

   This section describes a new Authentication TLV as:

Jethanandani, et al.      Expires May 15, 2019                  [Page 4]

Internet-Draft       BFD Authentication Optimization       November 2018

        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 TBD (NULL
   Auth TLV, to be assigned by IANA)

   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: This byte MUST be set to zero on transmit and ignored on

   Sequence Number: The sequence number for this packet.  Implementation
   may use sequence numbers as 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 to assign a new BFD Auth
   Type for "NULL Auth TLV" (see Section 3).

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

Jethanandani, et al.      Expires May 15, 2019                  [Page 5]

Internet-Draft       BFD Authentication Optimization       November 2018

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

              Jethanandani, M., Agarwal, S., Mishra, A., Saxena, A., and
              A. DeKok, "Secure BFD Sequence Numbers", draft-ietf-bfd-
              secure-sequence-numbers-02 (work in progress), May 2018.

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

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <>.

6.2.  Informative References

   [RFC1321]  Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321,
              DOI 10.17487/RFC1321, April 1992,

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

Jethanandani, et al.      Expires May 15, 2019                  [Page 6]

Internet-Draft       BFD Authentication Optimization       November 2018

              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


   Ashesh Mishra
   SES Networks


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


   Manav Bhatia


Jethanandani, et al.      Expires May 15, 2019                  [Page 7]