The TCP Authentication Option
RFC 5925

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Internet Engineering Task Force (IETF)                          J. Touch
Request for Comments: 5925                                       USC/ISI
Obsoletes: 2385                                                A. Mankin
Category: Standards Track                            Johns Hopkins Univ.
ISSN: 2070-1721                                                R. Bonica
                                                        Juniper Networks
                                                               June 2010

                     The TCP Authentication Option

Abstract

   This document specifies the TCP Authentication Option (TCP-AO), which
   obsoletes the TCP MD5 Signature option of RFC 2385 (TCP MD5).  TCP-AO
   specifies the use of stronger Message Authentication Codes (MACs),
   protects against replays even for long-lived TCP connections, and
   provides more details on the association of security with TCP
   connections than TCP MD5.  TCP-AO is compatible with either a static
   Master Key Tuple (MKT) configuration or an external, out-of-band MKT
   management mechanism; in either case, TCP-AO also protects
   connections when using the same MKT across repeated instances of a
   connection, using traffic keys derived from the MKT, and coordinates
   MKT changes between endpoints.  The result is intended to support
   current infrastructure uses of TCP MD5, such as to protect long-lived
   connections (as used, e.g., in BGP and LDP), and to support a larger
   set of MACs with minimal other system and operational changes.  TCP-
   AO uses a different option identifier than TCP MD5, even though TCP-
   AO and TCP MD5 are never permitted to be used simultaneously.  TCP-AO
   supports IPv6, and is fully compatible with the proposed requirements
   for the replacement of TCP MD5.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc5925.

Touch, et al.                Standards Track                    [Page 1]
RFC 5925              The TCP Authentication Option            June 2010

Copyright Notice

   Copyright (c) 2010 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
   (http://trustee.ietf.org/license-info) 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.

Touch, et al.                Standards Track                    [Page 2]
RFC 5925              The TCP Authentication Option            June 2010

Table of Contents

   1. Introduction ....................................................4
      1.1. Conventions Used in This Document ..........................4
      1.2. Applicability Statement ....................................5
      1.3. Executive Summary ..........................................6
   2. The TCP Authentication Option ...................................7
      2.1. Review of TCP MD5 Option ...................................7
      2.2. The TCP Authentication Option Format .......................8
   3. TCP-AO Keys and Their Properties ...............................10
      3.1. Master Key Tuple ..........................................10
      3.2. Traffic Keys ..............................................12
      3.3. MKT Properties ............................................13
   4. Per-Connection TCP-AO Parameters ...............................14
   5. Cryptographic Algorithms .......................................15
      5.1. MAC Algorithms ............................................15
      5.2. Traffic Key Derivation Functions ..........................18
      5.3. Traffic Key Establishment and Duration Issues .............22
           5.3.1. MKT Reuse Across Socket Pairs ......................22
           5.3.2. MKTs Use within a Long-Lived Connection ............23
   6. Additional Security Mechanisms .................................23
      6.1. Coordinating Use of New MKTs ..............................23
      6.2. Preventing Replay Attacks within Long-Lived Connections ...24
   7. TCP-AO Interaction with TCP ....................................26