Message Authentication Code for the Network Time Protocol
draft-ietf-ntp-mac-06

Document Type Active Internet-Draft (ntp WG)
Last updated 2019-04-11 (latest revision 2019-01-04)
Replaces draft-aanchal4-ntp-mac
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Internet Engineering Task Force                              A. Malhotra
Internet-Draft                                               S. Goldberg
Updates: 5905 (if approved)                            Boston University
Intended status: Standards Track                         January 4, 2019
Expires: July 8, 2019

       Message Authentication Code for the Network Time Protocol
                         draft-ietf-ntp-mac-06

Abstract

   RFC 5905 states that Network Time Protocol (NTP) packets should be
   authenticated by appending the NTP data to a 128-bit key, 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 as in RFC 4493 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 July 8, 2019.

Copyright Notice

   Copyright (c) 2019 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 the use of MD5  . . . . . . . . . . . . . . . . .   2
   3.  Replacement Recommendation  . . . . . . . . . . . . . . . . .   3
   4.  Motivation  . . . . . . . . . . . . . . . . . . . . . . . . .   3
   5.  Test Vectors  . . . . . . . . . . . . . . . . . . . . . . . .   3
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   3
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   4
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   4
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   4
     9.2.  Informative References  . . . . . . . . . . . . . . . . .   4
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   5

1.  Introduction

   RFC 5905 [RFC5905] states that Network Time Protocol (NTP) packets
   should be authenticated by appending the NTP data to a 128-bit key,
   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", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

2.  Deprecating the use of 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.

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3.  Replacement Recommendation

   If NTP authentication is implemented, then AES-CMAC as specified in
   RFC 4493 [RFC4493] MUST 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 MUST be 128
   bits long AES-128 key and the resulting MAC tag MUST be at least 128
   bits long as stated in section 2.4 of RFC 4493 [RFC4493].  NTP makes
   this transition possible as it supports algorithm agility as
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