< draft-schiff-ntp-chronos-01.txt   draft-schiff-ntp-chronos-02.txt >
Network Working Group N. R.Schiff Network Working Group N. R.Schiff
Internet-Draft D. Dolev Internet-Draft D. Dolev
Intended status: Informational Hebrew University of Jerusalem Intended status: Informational Hebrew University of Jerusalem
Expires: April 24, 2019 T. Mizrahi Expires: September 12, 2019 T. Mizrahi
Huawei Network.IO Innovation Lab Huawei Network.IO Innovation Lab
M. Schapira M. Schapira
Hebrew University of Jerusalem Hebrew University of Jerusalem
October 21, 2018 March 11, 2019
A Secure Selection and Filtering Mechanism for the Network Time Protocol A Secure Selection and Filtering Mechanism for the Network Time Protocol
Version 4 Version 4
draft-schiff-ntp-chronos-01 draft-schiff-ntp-chronos-02
Abstract Abstract
The Network Time Protocol version 4 (NTPv4) defines the peer process, The Network Time Protocol version 4 (NTPv4) defines the peer process,
the clock filter algorithm, the system process and the clock the clock filter algorithm, the system process and the clock
description algorithm. The clock filter algorithm and the system description algorithm. The clock filter algorithm and the system
process, as defined in RFC 5905, are the mechanism according to which process, as defined in RFC 5905, are the mechanism according to which
an NTP client chooses the NTP servers it synchronized with. This an NTP client chooses the NTP servers it synchronized with. This
document specifies an alternative set of client mechanisms, named document specifies an alternative set of client mechanisms, named
Chronos, that is backward compatible with NTPv4, and offers an Chronos, that is backward compatible with NTPv4, and offers an
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This Internet-Draft will expire on April 24, 2019. This Internet-Draft will expire on September 12, 2019.
Copyright Notice Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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// panic mode; // panic mode;
S := sample(n); S := sample(n);
T := bi-sided-trim(S,n/3) //trim bottom and top thrids; T := bi-sided-trim(S,n/3) //trim bottom and top thrids;
return avg(T) return avg(T)
5. Precision Vs. Security 5. Precision Vs. Security
Chronos client changes the list of the sampled servers more Chronos client changes the list of the sampled servers more
frequently than NTPv4 [Chronos_paper], without using NTPv4 filters. frequently than NTPv4 [Chronos_paper], without using NTPv4 filters.
This enables Chronos to be provably more secure than NTPv4 [RFC5905] This enables Chronos to be provably more secure than NTPv4 [RFC5905]
but might adversely affect its precision and accuracy. Such an but might adversely affect its precision and accuracy. Therefore we
effect is bounded by Chronos' w parameter that is set by default to add the following smoothing mechanism: Chronos returns the offset
25ms, which is appropriate for many applications [roughtime]. with minimal absolute value unless its distance from the average
offset is larger than a predefined value. Another approach we
considered was to use the same set of servers as in the previous
sample, unless the difference between the current offset and the new
offset is larger than a predefined value.
In scenarios where precision and accuracy are critical, a hybrid In our experiments we observed that with the smoothing mechanism,
approach can be applied: by default NTPv4 updates the local clock but Chornos and NTP are similar in terms of precision and accuracy when
when a threat or evidence of attack is detected (e.g., a system peer there is no attack.
is too far from the local clock) Chronos time is considered.
6. Acknowledgements 6. Acknowledgements
The authors would like to thank Miroslav Lichvar, Yaakov.J.Stein and The authors would like to thank Miroslav Lichvar, Yaakov.J.Stein and
Karen O'Donoghue for contributions to this document and helpful Karen O'Donoghue for contributions to this document and helpful
discussions and comments. discussions and comments.
7. IANA Considerations 7. IANA Considerations
This memo includes no request to IANA. This memo includes no request to IANA.
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