Public-Key Cryptography for the Network Time Protocol Version 2

Document Type Expired Internet-Draft (stime WG)
Author David Mills 
Last updated 2005-05-26 (latest revision 2002-11-05)
Stream Internet Engineering Task Force (IETF)
Intended RFC status Proposed Standard
Expired & archived
plain text pdf htmlized bibtex
Stream WG state WG Document
Document shepherd No shepherd assigned
IESG IESG state Expired (IESG: Dead)
Action Holders
Consensus Boilerplate Unknown
Telechat date
Responsible AD Russ Housley
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This document 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 premiss that IPSEC schemes cannot be adopted intact, since that would preclude stateless servers and severely compromise timekeeping accuracy. In addition, PKI schemes presume authenticated time values are always available to enforce certificate lifetimes; however, cryptographically verified timestamps require interaction between the timekeeping function and authentication function in ways not yet considered by the IETF. This Document 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 document has been implemented, tested and documented in the NTP Version 4 (NTPv4) software distribution for Unix, Windows and VMS at


David Mills (

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