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Message Authentication Code for the Network Time Protocol
draft-ietf-ntp-mac-03

The information below is for an old version of the document.
Document Type
This is an older version of an Internet-Draft that was ultimately published as RFC 8573.
Authors Aanchal Malhotra , Sharon Goldberg
Last updated 2017-10-30
Replaces draft-aanchal4-ntp-mac
RFC stream Internet Engineering Task Force (IETF)
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Document shepherd Karen O'Donoghue
IESG IESG state Became RFC 8573 (Proposed Standard)
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Send notices to Karen O'Donoghue <odonoghue@isoc.org>
draft-ietf-ntp-mac-03
Internet Engineering Task Force                              A. Malhotra
Internet-Draft                                               S. Goldberg
Intended status: Standards Track                       Boston University
Expires: May 3, 2018                                    October 30, 2017

       Message Authentication Code for the Network Time Protocol
                         draft-ietf-ntp-mac-03

Abstract

   RFC 5905 [RFC5905] states that Network Time Protocol (NTP) packets
   should be authenticated by appending a 128-bit key to the NTP data,
   and hashing the result with MD5 to obtain a 128-bit tag.  This
   document deprecates MD5-based authentication, which is considered to
   be too weak, and recommends the use of AES-CMAC [RFC4493] as a
   replacement.

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 May 3, 2018.

Copyright Notice

   Copyright (c) 2017 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 extracted from this document must
   include Simplified BSD License text as described in Section 4.e of

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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   2
   2.  Deprecating MD5 . . . . . . . . . . . . . . . . . . . . . . .   2
   3.  Replacement Recommendation  . . . . . . . . . . . . . . . . .   2
   4.  Motivation  . . . . . . . . . . . . . . . . . . . . . . . . .   3
   5.  Test Vectors  . . . . . . . . . . . . . . . . . . . . . . . .   3
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   3
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   3
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   3
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   3
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   4
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   4

1.  Introduction

   RFC 5905 [RFC5905] states that Network Time Protocol (NTP) packets
   should be authenticated by appending a 128-bit key to the NTP data,
   and hashing the result with MD5 to obtain a 128-bit tag.  This
   document deprecates MD5-based authentication, which is considered to
   be too weak, and recommends the use of AES-CMAC [RFC4493] as a
   replacement.

1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

2.  Deprecating MD5

   RFC 5905 [RFC5905] defines how the MD5 digest algorithm in RFC 1321
   [RFC1321] can be used as a message authentication code (MAC) for
   authenticating NTP packets.  However, as discussed in [BCK] and RFC
   6151 [RFC6151], this is not a secure MAC and therefore MUST be
   deprecated.

3.  Replacement Recommendation

   If authentication is implemented, then AES-CMAC as specified in RFC
   4493 [RFC4493] SHOULD be computed over all fields in the NTP header,
   and any extension fields that are present in the NTP packet as
   described in RFC 5905 [RFC5905].  The MAC key for NTP SHOULD be 128
   bits long AES-128 key and the resulting MAC tag SHOULD be 128 bits

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   long as stated in section 2.4 of RFC 4493 [RFC4493].  NTP makes this
   transition possible as it supports algorithm agility as described in
   Section 2.1 of RFC 7696 [RFC7696].

4.  Motivation

   AES-CMAC is recommended for the following reasons:

   1.  It is an IETF standard that is available in many open source
       implementations.

   2.  It is immune to nonce-reuse vulnerabilities (e.g.  [Joux])
       because it does not use a nonce.

   3.  It has fine performance in terms of latency and throughput.

   4.  It benefits from native hardware support, for instance, Intel's
       New Instruction set.

5.  Test Vectors

   For test vectors and their outputs refer to Section 4 of RFC 4493
   [RFC4493]

6.  Acknowledgements

   The authors wish to acknowledge useful discussions with Leen
   Alshenibr, Daniel Franke, Ethan Heilman, Kenny Paterson, Leonid
   Reyzin, Harlan Stenn, and Mayank Varia.

7.  IANA Considerations

   This memo includes no request to IANA.

8.  References

8.1.  Normative References

   [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/info/rfc2119>.

   [RFC4493]  Song, JH., Poovendran, R., Lee, J., and T. Iwata, "The
              AES-CMAC Algorithm", RFC 4493, DOI 10.17487/RFC4493, June
              2006, <https://www.rfc-editor.org/info/rfc4493>.

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   [RFC5905]  Mills, D., Martin, J., Ed., Burbank, J., and W. Kasch,
              "Network Time Protocol Version 4: Protocol and Algorithms
              Specification", RFC 5905, DOI 10.17487/RFC5905, June 2010,
              <https://www.rfc-editor.org/info/rfc5905>.

8.2.  Informative References

   [BCK]      Bellare, M., Canetti, R., and H. Krawczyk, "Keyed Hash
              Functions and Message Authentication", in Proceedings of
              Crypto'96, 1996.

   [Joux]     Joux, A., "Authentication Failures in NIST version of
              GCM",
              <http://csrc.nist.gov/groups/ST/toolkit/BCM/documents/
              comments/800-38_Series-Drafts/GCM/Joux_comments.pdf>.

   [RFC1321]  Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321,
              DOI 10.17487/RFC1321, April 1992,
              <https://www.rfc-editor.org/info/rfc1321>.

   [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,
              <https://www.rfc-editor.org/info/rfc6151>.

   [RFC7696]  Housley, R., "Guidelines for Cryptographic Algorithm
              Agility and Selecting Mandatory-to-Implement Algorithms",
              BCP 201, RFC 7696, DOI 10.17487/RFC7696, November 2015,
              <https://www.rfc-editor.org/info/rfc7696>.

Authors' Addresses

   Aanchal Malhotra
   Boston University
   111 Cummington St
   Boston, MA  02215
   US

   Email: aanchal4@bu.edu

   Sharon Goldberg
   Boston University
   111 Cummington St
   Boston, MA  02215
   US

   Email: goldbe@cs.bu.edu

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