Network Time Protocol Version 4: Autokey Specification
RFC 5906

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Internet Engineering Task Force (IETF)                  B. Haberman, Ed.
Request for Comments: 5906                                       JHU/APL
Category: Informational                                         D. Mills
ISSN: 2070-1721                                              U. Delaware
                                                               June 2010

         Network Time Protocol Version 4: Autokey Specification

Abstract

   This memo describes the Autokey security model for authenticating
   servers to clients using the Network Time Protocol (NTP) and public
   key cryptography.  Its design is based on the premise that IPsec
   schemes cannot be adopted intact, since that would preclude stateless
   servers and severely compromise timekeeping accuracy.  In addition,
   Public Key Infrastructure (PKI) schemes presume authenticated time
   values are always available to enforce certificate lifetimes;
   however, cryptographically verified timestamps require interaction
   between the timekeeping and authentication functions.

   This memo includes the Autokey requirements analysis, design
   principles, and protocol specification.  A detailed description of
   the protocol states, events, and transition functions is included.  A
   prototype of the Autokey design based on this memo has been
   implemented, tested, and documented in the NTP version 4 (NTPv4)
   software distribution for the Unix, Windows, and Virtual Memory
   System (VMS) operating systems at http://www.ntp.org.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Not all documents
   approved by the IESG are a candidate for any level of Internet
   Standard; see Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc5906.

Haberman & Mills              Informational                     [Page 1]
RFC 5906                      NTPv4 Autokey                    June 2010

Copyright Notice

   Copyright (c) 2010 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
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   publication of this document.  Please review these documents
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   described in the Simplified BSD License.

   This document may contain material from IETF Documents or IETF
   Contributions published or made publicly available before November
   10, 2008.  The person(s) controlling the copyright in some of this
   material may not have granted the IETF Trust the right to allow
   modifications of such material outside the IETF Standards Process.
   Without obtaining an adequate license from the person(s) controlling
   the copyright in such materials, this document may not be modified
   outside the IETF Standards Process, and derivative works of it may
   not be created outside the IETF Standards Process, except to format
   it for publication as an RFC or to translate it into languages other
   than English.

Haberman & Mills              Informational                     [Page 2]
RFC 5906                      NTPv4 Autokey                    June 2010

Table of Contents

   1. Introduction ....................................................4
   2. NTP Security Model ..............................................4
   3. Approach ........................................................7
   4. Autokey Cryptography ............................................8
   5. Autokey Protocol Overview ......................................12
   6. NTP Secure Groups ..............................................14
   7. Identity Schemes ...............................................19
   8. Timestamps and Filestamps ......................................20
   9. Autokey Operations .............................................22
   10. Autokey Protocol Messages .....................................23
      10.1. No-Operation .............................................26
      10.2. Association Message (ASSOC) ..............................26
      10.3. Certificate Message (CERT) ...............................26
      10.4. Cookie Message (COOKIE) ..................................27
      10.5. Autokey Message (AUTO) ...................................27