A Secure Selection and Filtering Mechanism for the Network Time Protocol Version 4

Document Type Replaced Internet-Draft (ntp WG)
Authors Neta Schiff  , Danny Dolev  , Tal Mizrahi  , Michael Schapira 
Last updated 2019-11-05 (latest revision 2019-09-03)
Replaced by draft-ietf-ntp-chronos
Stream IETF
Intended RFC status (None)
Expired & archived
pdf htmlized (tools) htmlized bibtex
Stream WG state Adopted by a WG
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IESG IESG state Replaced by draft-ietf-ntp-chronos
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This Internet-Draft is no longer active. A copy of the expired Internet-Draft can be found at


The Network Time Protocol version 4 (NTPv4) defines the peer process, the clock filter algorithm, the system process and the clock description algorithm. The clock filter algorithm and the system process, as defined in RFC 5905, are the mechanism according to which an NTP client chooses the NTP servers it synchronized with. This document specifies an alternative set of client mechanisms, named Chronos, that is backward compatible with NTPv4, and offers an improved level of security against time shifting attacks.


Neta Schiff (neta.r.schiff@gmail.com)
Danny Dolev (danny.dolev@mail.huji.ac.il)
Tal Mizrahi (tal.mizrahi.phd@gmail.com)
Michael Schapira (schapiram@huji.ac.il)

(Note: The e-mail addresses provided for the authors of this Internet-Draft may no longer be valid.)