A Secure Selection and Filtering Mechanism for the Network Time Protocol Version 4
draft-ietf-ntp-chronos-01

Document Type Active Internet-Draft (ntp WG)
Authors Neta Schiff  , Danny Dolev  , Tal Mizrahi  , Michael Schapira 
Last updated 2020-09-03
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: March 7, 2021                                        T. Mizrahi
                                        Huawei Network.IO Innovation Lab
                                                             M. Schapira
                                          Hebrew University of Jerusalem
                                                       September 3, 2020

A Secure Selection and Filtering Mechanism for the Network Time Protocol
                               Version 4
                       draft-ietf-ntp-chronos-01

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.

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
   Task Force (IETF).  Note that other groups may also distribute
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   This Internet-Draft will expire on March 7, 2021.

Copyright Notice

   Copyright (c) 2020 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 March 7, 2021                 [Page 1]
Internet-Draft         NTP Extention with Chronos         September 2020

   (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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   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
   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 . . . . . . . . . . . . .   4
     3.1.  Chronos' System Process . . . . . . . . . . . . . . . . .   5
   4.  Chronos' Pseudocode . . . . . . . . . . . . . . . . . . . . .   6
   5.  Precision vs. Security  . . . . . . . . . . . . . . . . . . .   7
   6.  Chronos' Threat Model and Security Guarantees . . . . . . . .   7
     6.1.  Security Analysis Overview  . . . . . . . . . . . . . . .   8
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   9
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   9
     9.2.  Informative References  . . . . . . . . . . . . . . . . .   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10

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 all NTP communications
   are encrypted and authenticated.  This document introduces an
   improved system process that incorporates an algorithm 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 a background mechanism that continuously maintains a
   virtual "Chronos" clock update and compares it to NTPv4's clock
   update.  When the gap between the two updates exceeds a certain
   threshold (specified in Section 6), this is interpreted as the client
   experiencing a time shifting attack.  In this case, Chronos is used
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