A Secure Selection and Filtering Mechanism for the Network Time Protocol
draft-ietf-ntp-chronos-02
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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This Internet-Draft will expire on August 25, 2021.
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This document is subject to BCP 78 and the IETF Trust's Legal
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Rozen-Schiff, et al. Expires August 25, 2021 [Page 1]
Internet-Draft NTP Extention with Chronos February 2021
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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 . . . . . . . . . . . . . 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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