A Secure Selection and Filtering Mechanism for the Network Time Protocol Version 4
draft-ietf-ntp-chronos-01
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
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Rozen-Schiff, et al. Expires March 7, 2021 [Page 1]
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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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