System time in anonymity oriented LiveCDs

[Thomas.Hluchnik at netcologne.de]

Without understanding details of the tor design, did you mention that tor knows the "real" time? So why dont you let tor set the right time. There could be a torrc setting like "when connecting to tor set system time according what tor says". This would enforce to run tor as root, not as unprivileged user, but this is a Live system, so this might be no problem(?).

Would this be a nice tor extension to help the LiveCD users?

Kind Regards

Thomas

Am Montag 03 Januar 2011 schrieb anonym:
> Hi list,
> 
> One issue for anonymity-oriented LiveCDs (such as T(A)ILS[1] and Liberté
> Linux[2]) is the system time. Tor requires a reasonably correct system
> time, otherwise no circuits will be opened. This is a major problem for
> these LiveCDs since they generally route all traffic through Tor
> transparently (using netfilter/iptables and the like) so no Tor circuits
> implies no network access for the user.
> 
> The obvious fix might seem to be to run something like NTP before Tor
> starts, but since NTP isn't authenticated at the moment[3] an adversary
> could intercept the NTP sync and force a crafted time on the user which
> later can be used to fingerprint the user if s/he uses some
> protocol/application which leaks system time. Hence NTP is out of the
> question.
> 
> Liberté Linux has a novel solution to this problem[4] -- it sets the
> system time according to the Tor consensus' valid-after/until values,
> which essentially removes Tor's time skew check. We T(A)ILS developers
> are tempted to implement the same solution, but first we'd like to ask
> here if this is safe, or if it opens up for any unexpected type of
> attacks or problems.
> 
> If any one has a completely different solution for the system time issue
> we're very interested in hearing that out as well.
> 
> Cheers!
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