



TCPM Working Group                                             R. Bonica
Internet-Draft                                                     T. Li
Updates: RFC 5926 (if approved)                                      HPE
Intended status: Standards Track                           27 April 2026
Expires: 29 October 2026


           Additional Security Algorithms For Use With TCP-AO
                     draft-ietf-tcpm-tcp-ao-algs-00

Abstract

   RFC5926 specifies cryptographic algorithms for TCP-AO.  It explains
   how to use KDF_HMAC_SHA1 and KDF_AES_128_CMAC as KDFs.  It also
   explains how to use HMAC-SHA-1-96 and AES-128-CMAC-96 as MAC
   algorithms.

   This document specifies several new KDFs and MAC algorithms for TCP-
   AO.  The KDFs and MAC algorithms specified in this document use
   stronger cryptography.

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 https://datatracker.ietf.org/drafts/current/.

   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 29 October 2026.

Copyright Notice

   Copyright (c) 2026 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 (https://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



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   extracted from this document must include Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions and Definitions . . . . . . . . . . . . . . . . .   4
   3.  Updates to RFC 5926 . . . . . . . . . . . . . . . . . . . . .   4
     3.1.  Concrete KDFs . . . . . . . . . . . . . . . . . . . . . .   4
       3.1.1.  KDF_HMAC_SHA256 . . . . . . . . . . . . . . . . . . .   4
       3.1.2.  KDF_HMAC_SHA384 . . . . . . . . . . . . . . . . . . .   4
       3.1.3.  KDF_HMAC_SHA512 . . . . . . . . . . . . . . . . . . .   5
       3.1.4.  KDF_HMAC_SHA3-256 . . . . . . . . . . . . . . . . . .   5
       3.1.5.  KDF_HMAC_SHA3-384 . . . . . . . . . . . . . . . . . .   5
       3.1.6.  KDF_HMAC_SHA3-512 . . . . . . . . . . . . . . . . . .   6
     3.2.  MAC Algorithms  . . . . . . . . . . . . . . . . . . . . .   6
       3.2.1.  The Use of HMAC-SHA256-128  . . . . . . . . . . . . .   6
       3.2.2.  The Use of HMAC-SHA384-128  . . . . . . . . . . . . .   7
       3.2.3.  The Use of HMAC-SHA512-128  . . . . . . . . . . . . .   7
       3.2.4.  The Use of HMAC-SHA3-256-128  . . . . . . . . . . . .   8
       3.2.5.  The Use of HMAC-SHA3-384-128  . . . . . . . . . . . .   9
       3.2.6.  The Use of HMAC-SHA3-512-128  . . . . . . . . . . . .   9
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .  10
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  10
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  11
   7.  Normative References  . . . . . . . . . . . . . . . . . . . .  11
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  12

1.  Introduction

   TCP end-points use the TCP Authentication Option (TCP-AO) [RFC5925]
   to authenticate segments.  TCP-AO relies upon:

   *  A Master Key Tuple (MKT)

   *  A Key Derivation Function (KDF)

   *  A Message Authentication Code (MAC) algorithm

   TCP-AO systems are configured with one or more MKTs for each
   connection that they protect.  When a connection is associated with
   multiple MKTs, TCP-AO can rotate among them during the course of a
   TCP session.  This facilitates dynamic key change and authentication
   algorithm agility.

   An MKT includes:




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   *  Two MKT identifiers, one used for sending and one used for
      receiving

   *  A connection identifier (i.e., a TCP socket pair)

   *  A master key (i.e., a shared secret)

   *  A KDF

   *  A MAC algorithm

   *  A flag indicating whether TCP options other than TCP-AO are
      authenticated

   The KDF generates a traffic key.  Its inputs are:

   *  A pseudorandom function (PRF) used to generate the traffic key

   *  The master key

   *  Context (i.e., A binary string containing information related to
      the connection)

   *  Output length (i.e., the length of the traffic key, in bits)

   The MAC algorithm produces a MAC.  It is defined by:

   *  The KDF algorithm used to generate the traffic key

   *  The length of the traffic key, in bits

   *  The length of the MAC, in bits

   The following are inputs to the MAC Algorithm:

   *  traffic key

   *  message

   TCP-AO systems include the MAC in the TCP-AO.  They use the MAC to
   authenticate segments.

   [RFC5926] specifies cryptographic algorithms for TCP-AO.  It explains
   how to use KDF_HMAC_SHA1 and KDF_AES_128_CMAC as KDFs.  It also
   explains how to use HMAC-SHA-1-96 and AES-128-CMAC-96 as MAC
   algorithms.





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   This document specifies several new KDFs and MAC algorithms for TCP-
   AO.  The KDFs and MAC algorithms defined in this document use
   stronger cryptography.

   According to [RFC2104], "Applications of HMAC can choose to truncate
   the output of HMAC by outputting the t leftmost bits of the HMAC
   computation for some parameter t".

   The algorithms described in this document truncate the output of HMAC
   to 128 bits (i.e., 16 bytes).  Therefore, when they are encoded in
   TCP-AO, the TCP-AO consumes 20 bytes.

2.  Conventions and Definitions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   BCP14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

3.  Updates to RFC 5926

3.1.  Concrete KDFs

3.1.1.  KDF_HMAC_SHA256

   For KDF_HMAC_SHA256:

   *  PRF for KDF_alg: HMAC-SHA256 [RFC2104]
      [DOI.10.6028_NIST.FIPS.180-4]

   *  Use: HMAC-SHA256(Key, Input).

   *  Input: ( i || Label || Context || Output_Length)

   *  Key: Master_Key, configured by user, and passed to the KDF

   *  Output_Length: 256 bits

   *  Result: Traffic_Key, used in the MAC function by TCP-AO

3.1.2.  KDF_HMAC_SHA384

   For KDF_HMAC_SHA384:

   *  PRF for KDF_alg: HMAC-SHA384 [RFC2104]
      [DOI.10.6028_NIST.FIPS.180-4]




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   *  Use: HMAC-SHA384(Key, Input).

   *  Input: ( i || Label || Context || Output_Length)

   *  Key: Master_Key, configured by user, and passed to the KDF

   *  Output_Length: 384 bits

   *  Result: Traffic_Key, used in the MAC function by TCP-AO

3.1.3.  KDF_HMAC_SHA512

   For KDF_HMAC_SHA512:

   *  PRF for KDF_alg: HMAC-SHA512 [RFC2104]
      [DOI.10.6028_NIST.FIPS.180-4]

   *  Use: HMAC-SHA512(Key, Input).

   *  Input: ( i || Label || Context || Output_Length)

   *  Key: Master_Key, configured by user, and passed to the KDF

   *  Output_Length: 512 bits

   *  Result: Traffic_Key, used in the MAC function by TCP-AO

3.1.4.  KDF_HMAC_SHA3-256

   For KDF_HMAC_SHA3-256:

   *  PRF for KDF_alg: HMAC-SHA3-256 [RFC2104]
      [DOI.10.6028_NIST.FIPS.202]

   *  Use: HMAC-SHA3-256(Key, Input).

   *  Input: ( i || Label || Context || Output_Length)

   *  Key: Master_Key, configured by user, and passed to the KDF

   *  Output_Length: 256 bits

   *  Result: Traffic_Key, used in the MAC function by TCP-AO

3.1.5.  KDF_HMAC_SHA3-384

   For KDF_HMAC_SHA3-384:




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   *  PRF for KDF_alg: HMAC-SHA3-384 [RFC2104]
      [DOI.10.6028_NIST.FIPS.202]

   *  Use: HMAC-SHA3-384(Key, Input).

   *  Input: ( i || Label || Context || Output_Length)

   *  Key: Master_Key, configured by user, and passed to the KDF

   *  Output_Length: 384 bits

   *  Result: Traffic_Key, used in the MAC function by TCP-AO

3.1.6.  KDF_HMAC_SHA3-512

   For KDF_HMAC_SHA3-512:

   *  PRF for KDF_alg: HMAC-SHA3-512 [RFC2104]
      [DOI.10.6028_NIST.FIPS.202]

   *  Use: HMAC-SHA3-512(Key, Input).

   *  Input: ( i || Label || Context || Output_Length)

   *  Key: Master_Key, configured by user, and passed to the KDF

   *  Output_Length: 512 bits

   *  Result: Traffic_Key, used in the MAC function by TCP-AO

3.2.  MAC Algorithms

   The following subsections should be added to Section 3.2 of
   [RFC5926].

3.2.1.  The Use of HMAC-SHA256-128

   By definition, HMAC [RFC2104] requires a cryptographic hash function.
   SHA256 will be that hash function used for authenticating and
   providing integrity validation on TCP segments with HMAC.

   The three fixed elements for HMAC-SHA256-128 are:

   *  KDF_Alg: KDF_HMAC_SHA256

   *  Key_Length: 256 bits.

   *  MAC_Length: 128 bits.



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   For:

   *  MAC = MAC_alg (Traffic_Key, Message)

   HMAC-SHA256-128 for TCP-AO has the following values:

   *  MAC_alg: HMAC-SHA256

   *  Traffic_Key: Variable; the result of the KDF.

   *  Message: The message to be authenticated, as specified in
      [RFC5925], Section 5.1.

3.2.2.  The Use of HMAC-SHA384-128

   By definition, HMAC [RFC2104] requires a cryptographic hash function.
   SHA384 will be that hash function used for authenticating and
   providing integrity validation on TCP segments with HMAC.

   The three fixed elements for HMAC-SHA384-128 are:

   *  KDF_Alg: KDF_HMAC_SHA384

   *  Key_Length: 384 bits.

   *  MAC_Length: 128 bits.

   For:

   *  MAC = MAC_alg (Traffic_Key, Message)

   HMAC-SHA384-128 for TCP-AO has the following values:

   *  MAC_alg: HMAC-SHA384

   *  Traffic_Key: Variable; the result of the KDF.

   *  Message: The message to be authenticated, as specified in
      [RFC5925], Section 5.1.

3.2.3.  The Use of HMAC-SHA512-128

   By definition, HMAC [RFC2104] requires a cryptographic hash function.
   SHA512 will be that hash function used for authenticating and
   providing integrity validation on TCP segments with HMAC.

   The three fixed elements for HMAC-SHA512-128 are:




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   *  KDF_Alg: KDF_HMAC_SHA512

   *  Key_Length: 512 bits.

   *  MAC_Length: 128 bits.

   For:

   *  MAC = MAC_alg (Traffic_Key, Message)

   HMAC-SHA512-128 for TCP-AO has the following values:

   *  MAC_alg: HMAC-SHA512

   *  Traffic_Key: Variable; the result of the KDF.

   *  Message: The message to be authenticated, as specified in
      [RFC5925], Section 5.1.

3.2.4.  The Use of HMAC-SHA3-256-128

   By definition, HMAC [RFC2104] requires a cryptographic hash function.
   SHA3-256 will be that hash function used for authenticating and
   providing integrity validation on TCP segments with HMAC.

   The three fixed elements for HMAC-SHA3-256-128 are:

   *  KDF_Alg: KDF_HMAC_SHA3-256.

   *  Key_Length: 256 bits.

   *  MAC_Length: 128 bits.

   For:

   *  MAC = MAC_alg (Traffic_Key, Message)

   HMAC-SHA3-256-128 for TCP-AO has the following values:

   *  MAC_alg: HMAC-SHA3-256.

   *  Traffic_Key: Variable; the result of the KDF.

   *  Message: The message to be authenticated, as specified in
      [RFC5925], Section 5.1.






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3.2.5.  The Use of HMAC-SHA3-384-128

   By definition, HMAC [RFC2104] requires a cryptographic hash function.
   SHA3-384 will be that hash function used for authenticating and
   providing integrity validation on TCP segments with HMAC.

   The three fixed elements for HMAC-SHA3-384-128 are:

   *  KDF_Alg: KDF_HMAC_SHA3-384.

   *  Key_Length: 384 bits.

   *  MAC_Length: 128 bits.

   For:

   *  MAC = MAC_alg (Traffic_Key, Message)

   HMAC-SHA3-384-128 for TCP-AO has the following values:

   *  MAC_alg: HMAC-SHA3-384.

   *  Traffic_Key: Variable; the result of the KDF.

   *  Message: The message to be authenticated, as specified in
      [RFC5925], Section 5.1.

3.2.6.  The Use of HMAC-SHA3-512-128

   By definition, HMAC [RFC2104] requires a cryptographic hash function.
   SHA3-512 will be that hash function used for authenticating and
   providing integrity validation on TCP segments with HMAC.

   The three fixed elements for HMAC-SHA3-512-128 are:

   *  KDF_Alg: KDF_HMAC_SHA3-512.

   *  Key_Length: 512 bits.

   *  MAC_Length: 128 bits.

   For:

   *  MAC = MAC_alg (Traffic_Key, Message)

   HMAC-SHA3-512-128 for TCP-AO has the following values:

   *  MAC_alg: HMAC-SHA3-512.



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   *  Traffic_Key: Variable; the result of the KDF.

   *  Message: The message to be authenticated, as specified in
      [RFC5925], Section 5.1.

4.  Security Considerations

   According to [RFC2104], "Applications of HMAC can choose to truncate
   the output of HMAC by outputting the t leftmost bits of the HMAC
   computation for some parameter t".

   The algorithms described in this document truncate the output of HMAC
   to 128 bits (i.e., 16 bytes).  Therefore, when they are encoded in
   TCP-AO, the TCP-AO consumes 20 bytes.

   [RFC2104] continues, "We recommend that the output length t be not
   less than half the length of the hash output (to match the birthday
   attack bound) and not less than 80 bits (a suitable lower bound on
   the number of bits that need to be predicted by an attacker).

   In this document, only the following MAC algorithms comply with that
   recommendation:

   *  HMAC-SHA256-128

   *  HMAC-SHA3-256-128

5.  IANA Considerations

   IANA is requested to add the following entries to the "Cryptographic
   Algorithms for TCP-AO Registration"
   (https://www.iana.org/assignments/tcp-parameters/tcp-
   parameters.xhtml#tcp-parameters-3).


















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                     +==============+===============+
                     | Algorithm    | Reference     |
                     +==============+===============+
                     | SHA256-128   | This Document |
                     +--------------+---------------+
                     | SHA384-128   | This Document |
                     +--------------+---------------+
                     | SHA512-128   | This Document |
                     +--------------+---------------+
                     | SHA3-256-128 | This Document |
                     +--------------+---------------+
                     | SHA3-384-128 | This Document |
                     +--------------+---------------+
                     | SHA3-512-128 | This Document |
                     +--------------+---------------+

                          Table 1: IANA Actions

6.  Acknowledgements

   Thanks to Lars Eggert, Gorry Fairhurst, C.M.  Heard, Russ Housley,
   John Mattsson, Yoshifumi Nishida, Joe Touch, Michael Tuxen, and
   Magnus Westerlund for their review and comments.

7.  Normative References

   [DOI.10.6028_NIST.FIPS.180-4]
              "Secure hash standard", National Institute of Standards
              and Technology (U.S.), DOI 10.6028/nist.fips.180-4, 2015,
              <https://doi.org/10.6028/nist.fips.180-4>.

   [DOI.10.6028_NIST.FIPS.197]
              "Advanced Encryption Standard (AES)", National Institute
              of Standards and Technology (U.S.),
              DOI 10.6028/nist.fips.197, 2001,
              <https://doi.org/10.6028/nist.fips.197>.

   [DOI.10.6028_NIST.FIPS.202]
              "SHA-3 standard :: permutation-based hash and extendable-
              output functions", National Institute of Standards and
              Technology (U.S.), DOI 10.6028/nist.fips.202, 2015,
              <https://doi.org/10.6028/nist.fips.202>.









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   [DOI.10.6028_NIST.SP.800-38B]
              Dworkin, M., "Recommendation for block cipher modes of
              operation :: the CMAC mode for authentication", National
              Institute of Standards and Technology,
              DOI 10.6028/nist.sp.800-38b, 2016,
              <https://doi.org/10.6028/nist.sp.800-38b>.

   [RFC2104]  Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-
              Hashing for Message Authentication", RFC 2104,
              DOI 10.17487/RFC2104, February 1997,
              <https://www.rfc-editor.org/rfc/rfc2104>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/rfc/rfc2119>.

   [RFC4615]  Song, J., Poovendran, R., Lee, J., and T. Iwata, "The
              Advanced Encryption Standard-Cipher-based Message
              Authentication Code-Pseudo-Random Function-128 (AES-CMAC-
              PRF-128) Algorithm for the Internet Key Exchange Protocol
              (IKE)", RFC 4615, DOI 10.17487/RFC4615, August 2006,
              <https://www.rfc-editor.org/rfc/rfc4615>.

   [RFC5925]  Touch, J., Mankin, A., and R. Bonica, "The TCP
              Authentication Option", RFC 5925, DOI 10.17487/RFC5925,
              June 2010, <https://www.rfc-editor.org/rfc/rfc5925>.

   [RFC5926]  Lebovitz, G. and E. Rescorla, "Cryptographic Algorithms
              for the TCP Authentication Option (TCP-AO)", RFC 5926,
              DOI 10.17487/RFC5926, June 2010,
              <https://www.rfc-editor.org/rfc/rfc5926>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/rfc/rfc8174>.

Authors' Addresses

   Ron Bonica
   HPE
   United States of America
   Email: ronald.bonica@hpe.com


   Tony Li
   HPE
   United States of America



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   Email: tony.li@tony.li


















































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