Network Time Protocol MAC/Last Extension Fields
draft-stenn-ntp-mac-last-ef-04

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Last updated 2019-03-25
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Internet Engineering Task Force                                 H. Stenn
Internet-Draft                                                  D. Mayer
Intended status: Standards Track                 Network Time Foundation
Expires: September 26, 2019                               March 25, 2019

            Network Time Protocol MAC/Last Extension Fields
                     draft-stenn-ntp-mac-last-ef-04

Abstract

   NTP packets can be authenticated by a Message Authentication Code
   (MAC) if a MAC is present at the end of an NTP packet.  The legacy
   format for this MAC is not formatted as an NTP Extension Field, and
   its presence may cause some implementations a parsing ambiguity.

   This proposal introduces two ways to resolve this problem.  One is to
   provide a MAC Extension Field.  The other is an extension field that
   unambiguously declares itself to be the last extension field in an
   NTP packet (so any additional data MUST be a legacy MAC).

   RFC EDITOR: PLEASE REMOVE THE FOLLOWING PARAGRAPH BEFORE PUBLISHING:

   The source code and issues list for this draft can be found in
   https://github.com/hstenn/ietf-ntp-mac-last-ef

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on September 26, 2019.

Copyright Notice

   Copyright (c) 2019 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

Stenn & Mayer          Expires September 26, 2019               [Page 1]
Internet-Draft        NTP MAC/Last Extension Fields           March 2019

   This document is subject to BCP 78 and the IETF Trust's Legal
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   (https://trustee.ietf.org/license-info) in effect on the date of
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   2
   2.  The Last Extension Field Extension Field - LAST-EF  . . . . .   3
   3.  MAC Extension Field . . . . . . . . . . . . . . . . . . . . .   4
   4.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   6
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   7.  Normative References  . . . . . . . . . . . . . . . . . . . .   7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

1.  Introduction

   NTPv4 is defined by RFC 5905 [RFC5905], and it and earlier versions
   of the NTP Protocol have supported symmetric private key Message
   Authentication Code (MAC) authentication.  MACs were first described
   in Appendix C of RFC 1305 [RFC1305] and are further described in RFC
   5905 [RFC5905].  As the number of Extension Fields grows there is an
   increasing chance some implementations will find a parsing ambiguity
   when deciding if the "next" set of data is an Extension Field or a
   legacy MAC.  This proposal defines two new Extension Fields to avoid
   this potential ambiguity.  One, LAST-EF, is used to signify that it
   is the last Extension Field in the packet.  If the LAST-EF is
   present, any subsequent data MUST be considered to be a legacy MAC,
   or if you prefer, any subsequent data MUST NOT be considered to be an
   EF.  The other, MAC-EF, allows one or more MACs to be encapsulated in
   an Extension Field.  If all parties in an association support MAC-EF,
   the use of a legacy MAC may be avoided.

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].

Stenn & Mayer          Expires September 26, 2019               [Page 2]
Internet-Draft        NTP MAC/Last Extension Fields           March 2019

2.  The Last Extension Field Extension Field - LAST-EF

   Now that multiple extension fields are a possibility, additional
   packet data could be either an Extension Field or a legacy MAC.
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