A Secure Selection and Filtering Mechanism for the Network Time Protocol
draft-ietf-ntp-chronos-02

Document Type Active Internet-Draft (ntp WG)
Authors Neta Schiff  , Danny Dolev  , Tal Mizrahi  , Michael Schapira 
Last updated 2021-02-21
Replaces draft-schiff-ntp-chronos
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Network Working Group                                    N. Rozen-Schiff
Internet-Draft                                                  D. Dolev
Intended status: Informational            Hebrew University of Jerusalem
Expires: August 25, 2021                                      T. Mizrahi
                                        Huawei Network.IO Innovation Lab
                                                             M. Schapira
                                          Hebrew University of Jerusalem
                                                       February 21, 2021

A Secure Selection and Filtering Mechanism for the Network Time Protocol
                       draft-ietf-ntp-chronos-02

Abstract

   The Network Time Protocol version 4 (NTPv4), as defined in RFC 5905,
   is the mechanism used by NTP clients to synchronize with NTP servers
   across the Internet.  This document specifies an extension to the
   NTPv4 client, named Chronos, which is used as a "watchdog" alongside
   NTPv4, and provides improved security against time shifting attacks.
   Chronos involves changes to the NTP client's system process only and
   is backwards compatible with NTPv4 servers.  Chronos is also
   compatible with NTPv5, since it does not affect the wire protocol.

Status of This Memo

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   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on August 25, 2021.

Copyright Notice

   Copyright (c) 2021 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

Rozen-Schiff, et al.     Expires August 25, 2021                [Page 1]
Internet-Draft         NTP Extention with Chronos          February 2021

   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions Used in This Document . . . . . . . . . . . . . .   4
     2.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   4
     2.2.  Terms and Abbreviations . . . . . . . . . . . . . . . . .   4
     2.3.  Notations . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Extension to the NTP System Process . . . . . . . . . . . . .   5
     3.1.  Chronos' System Process . . . . . . . . . . . . . . . . .   6
     3.2.  Chronos' Recommended Parameters . . . . . . . . . . . . .   7
   4.  Chronos' Pseudocode . . . . . . . . . . . . . . . . . . . . .   7
   5.  Precision vs. Security  . . . . . . . . . . . . . . . . . . .   8
   6.  Chronos' Threat Model and Security Guarantees . . . . . . . .   8
     6.1.  Security Analysis Overview  . . . . . . . . . . . . . . .   9
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  10
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  10
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  10
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  10
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  11

1.  Introduction

   NTPv4, as defined in RFC 5905 [RFC5905], is vulnerable to time
   shifting attacks, in which the attacker's goal is to shift the local
   time at an NTP client.  See [Chronos_paper] for details.  Time
   shifting attacks on NTP are possible even if NTP communication is
   encrypted and authenticated.  A weaker man-in-the-middle (MitM)
   attacker can shift time simply by dropping or delaying packets,
   whereas a powerful attacker, who has full control over an NTP server,
   can determine the response content.  This document introduces a time
   shifting mitigation mechanism called Chronos.  Chronos is backwards
   compatible with NTPv4 and serves as an NTPv4 client's "watchdog" for
   time shifting attacks.  An NTP client that runs Chronos is
   interoperable with [RFC5905]-compatible NTPv4 servers.  Chronos is
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