Message Authentication Codes for the Network Time Protocol
draft-aanchal4-ntp-mac-01

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Last updated 2016-10-13
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Internet Engineering Task Force                              A. Malhotra
Internet-Draft                                               S. Goldberg
Intended status: Standards Track                       Boston University
Expires: April 16, 2017                                 October 13, 2016

       Message Authentication Codes for the Network Time Protocol
                       draft-aanchal4-ntp-mac-01

Abstract

   The Network Time Protocol (NTP) RFC 5905 [RFC5905] uses a message
   authentication code (MAC) to cryptographically authenticate its UDP
   packets.  Currently, NTP packets are authenticated by appending a
   128-bit key to the NTP data, and hashing the result with MD5 to
   obtain a 128-bit tag.  However, as discussed in [BCK] and [RFC6151],
   this not a secure MAC.  As such, this draft considers different
   secure MAC algorithms for use with NTP, evaluates their performance,
   and recommends the use CMAC-AES [RFC4493].  We also suggest
   deprecating the use of MD5 as defined in [RFC5905] for authenticating
   NTP packets.

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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   Internet-Drafts are draft documents valid for a maximum of six months
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   This Internet-Draft will expire on April 16, 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
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents

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   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
   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.  MAC Algorithms  . . . . . . . . . . . . . . . . . . . . . . .   2
   3.  Requirements  . . . . . . . . . . . . . . . . . . . . . . . .   3
     3.1.  Performance Requirements  . . . . . . . . . . . . . . . .   3
     3.2.  Security Requirements . . . . . . . . . . . . . . . . . .   4
   4.  Performance Results . . . . . . . . . . . . . . . . . . . . .   4
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
     5.1.  Why is GMAC not suitable for NTP? . . . . . . . . . . . .   6
     5.2.  Use HMAC or CMAC instead? . . . . . . . . . . . . . . . .   8
   6.  Recommendations . . . . . . . . . . . . . . . . . . . . . . .   8
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   8
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   8
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Introduction

   NTP uses a message authentication code (MAC) to authenticate its
   packets.  Currently, NTP packets are authenticated by appending a
   128-bit key to the NTP data, and hashing the result with MD5 to
   obtain a 128-bit tag.  However, as discussed in [BCK] and [RFC6151],
   this not a secure MAC.  As such, this draft considers different
   secure MAC algorithms for use with NTP, evaluates their performance,
   and and recommends the use CMAC-AES [RFC4493].  We also suggest
   deprecating the use of MD5, as defined in [RFC5905], for
   authenticating NTP packets.

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.  MAC Algorithms

   We consider five diverse MAC algorithms, which encompass hash-based
   HMAC-MD5 and HMAC-SHA224 [RFC2104], block cipher-based CMAC-AES
   [RFC4493], and universal hashing-based Galois MAC (GMAC) [RFC4543]

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