Message Authentication Code for the Network Time Protocol
draft-ietf-ntp-mac-00

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Last updated 2017-01-05
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Internet Engineering Task Force                              A. Malhotra
Internet-Draft                                               S. Goldberg
Intended status: Standards Track                       Boston University
Expires: May 27, 2017                                  November 23, 2016

       Message Authentication Code for the Network Time Protocol
                         draft-ietf-ntp-mac-00

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 the authentication of NTP packets with MD5 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
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   This Internet-Draft will expire on May 27, 2017.

Copyright Notice

   Copyright (c) 2016 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
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   described in the Simplified BSD License.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   2
   2.  Deprecating MD5 . . . . . . . . . . . . . . . . . . . . . . .   2
   3.  Replacement Recommendation  . . . . . . . . . . . . . . . . .   2
   4.  Motivation  . . . . . . . . . . . . . . . . . . . . . . . . .   3
   5.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   3
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   3
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .   3
     6.2.  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 the authentication of NTP packets with MD5 and
   recommends the use of AES-CMAC RFC 4493 [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,
   as well as the NTP key-id field, and any NTP extension fields that
   are present in the NTP packet.  We recommend that the MAC key for NTP
   should be 128 bits long AES-128 key and the resulting MAC tag should
   be 128 bits long as stated in section 2.4 of RFC 4493 [RFC4493].

Malhotra & Goldberg       Expires May 27, 2017                  [Page 2]
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