Re: [TICTOC] Updated draft-ietf-tictoc-security-requirements-07

Tal Mizrahi <> Tue, 29 April 2014 05:04 UTC

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From: Tal Mizrahi <>
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Date: Tue, 29 Apr 2014 08:04:01 +0300
Thread-Topic: [TICTOC] Updated draft-ietf-tictoc-security-requirements-07
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Subject: Re: [TICTOC] Updated draft-ietf-tictoc-security-requirements-07
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Dieter, thanks for the comments.
After some further offline discussion with Dieter, I understand the concern: in section 5.1.3 WRT authentication we actually implied two different requirements: (i) master authenticates the identity of the slave, and (ii) slave spoofing prevention.  As Dieter explains, (ii) can be satisfied even when (i) is not satisfied.

My suggestion is as follows:
Add a new subsection, “5.x Spoofing Prevention”, that requires a mechanism that prevents (i) master (server) spoofing. (ii) slave (client) spoofing, and (iii) TC spoofing (in PTP).
This new section will be a MUST.
We can then change 5.1.3 and 5.1.4 back to MAY.

Please let me know if there are further comments.


From: []
Sent: Thursday, April 24, 2014 7:23 PM
To: Tal Mizrahi
Subject: Re: [TICTOC] Updated draft-ietf-tictoc-security-requirements-07

Hello Tal,

I have one comment regarding Sec. 5.1.3.

This section requires that the master MUST authenticate each client. I think that this requirement should be a MAY! In the case of a public time service there is no need for the master to authenticate its slaves. The spoofing attack described in the second example of 3.2.2 can be mitigated by other means such as the introduction of a nonce in a time request or delay_req message.

I agree that in the case of authorization of the slave authentication is also necessary.


Physikalisch-Technische Bundesanstalt
Dr. Dieter Sibold
Q.42 - Serversysteme und Datenhaltung
QM-Verantwortlicher der Stelle IT-Infrastruktur
Bundesallee 100
D-38116 Braunschweig
Tel: +49-531-592-84 20

Von:        Tal Mizrahi <<>>
An:        "<>" <<>>, "Yaakov Stein (<>)" <<>>, "<>" <<>>
Kopie:        "Shawn M Emery \(\<\>)" <<>>
Datum:        23.04.2014 14:40
Betreff:        [TICTOC] Updated draft-ietf-tictoc-security-requirements-07
Gesendet von:        "TICTOC" <<>>


I have posted an updated draft.

The most notable changes in this draft:
1.       I updated the draft to address comments from Shawn, the appointed secdir reviewer:
2.       I updated the draft to address comments from Russell Smiley:
This includes:
- In section 5.1.3 and 5.1.4 we decoupled the authentication and authorization requirements. The authentication requirement level was changed to ‘MUST’ following the good observation made by Russell: “Absence of authentication of slaves may enable MITM attacks delaying delay_req packets and thereby distorting the delay_req packet arrival times and subsequent departure of delay_resp. The resulting asymmetry could distort the subsequent slave clock offset calculations.”
- The authorization requirement remains ‘MAY’ for sections 5.1.3 and 5.1.4.
3.       The requirement level of section 5.8 was changed to ‘MUST’. The background is the insight that MITM attacks (sections 3.2.5, 3.2.6) have the same impact and level of difficulty to implement as manipulation attacks (section 3.2.1). Hence, a similar requirement level is called for in the two cases.
Section 5.8 also clarifies that: “While the security mechanism should support the ability to detect delay attacks, it is noted that in some networks it is not possible to provide the redundancy needed for such a detection mechanism.”
4.       Section 5.2: merged the two sub-requirements to a single requirement for integrity protection. The previous phrasing called for hop-by-hop integrity protection as a MUST and end-to-end as a SHOULD, but some of the feedback we received was that in some scenarios or network topologies an end-to-end may provide a higher level of security. The current phrasing just presents the tradeoff between peer-to-peer and end-to-end.

Please let me know if there are any comments.

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