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[liberationtech] NSA, FBI, Verizon caught red handed spying on US citizens in the US

Richard Brooks rrb at acm.org
Fri Jun 7 07:20:26 PDT 2013


On 06/07/2013 03:23 AM, Seth David Schoen wrote:

> The best widely-used tool to defend against traffic analysis is Tor,
> but Tor's developers readily concede that it has a lot of important
> limitations and that there's no obvious path around many of them.
> Two of these important limitations (not the only ones) are:
> 
> ① Anonymization adds latency to communications.  Better anonymization
> usually adds more latency.  Everywhere else, communications engineers
> are struggling to take the latency out of people's communications.
> At least in some systems, anonymity engineers are struggling to put
> it in.
> 
> ② Network adversaries can notice that things coming out of a system
> correspond to things going in.
> 
> Here's one of many statements of these two issues as they relate to
> systems like Tor:
> 
>    Furthermore, Onion Routing makes no attempt to stop timing attacks
>    using traffic analysis at the network endpoints. They assume that
>    the routing infrastructure is uniformly busy, thus making passive
>    intra-network timing difficult. However, the network might not
>    be statistically uniformly busy, and attackers can tell if two
>    parties are communicating via increased traffic at their respective
>    endpoints. This endpoint-linkable timing attack remains a difficulty
>    for all low-latency networks.
> 
> http://www.freehaven.net/src/related-comm.thtml
> 
> These issues are less severe if people are using e-mail or (maybe
> better yet) forum posting, over an encrypted channel to a popular
> service that many people use.  But they're quite serious for voice
> calls, video conferencing, and even instant messaging.
> 
We were able to do our timing side-channel approach on Tor very
successfully on a private Tor instance in our lab. When we tried
it on the global net, we found the jitter inherent to Tor made
it practically impossible.

Have not tried it specifically on VOIP traffic, but the latency/jitter
seems to me to do a pretty good job of making timing attacks
unreliable for now.

-RRB



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