Thus spake Paul Syverson (syverson@xxxxxxxxxxxxxxxx): > Anyway, the main reason I'm writing is that my objection was not just > that the GPA was too strong but that it was too weak. Thinking you > could have an adversary powerful enough to monitor all the links > necessary to watch your whole large network but not able to do any > active traffic shaping at all anywhere seems obviously nuts. This is > one reason why padding on an open low-latency (lossless) network is > problematic: an adversary with any active capability at all can induce > a timing channel easily. Actually, I'm going to disagree slightly because I don't feel like sleeping yet :). It would take far less resources to passively tap the traffic and filter out say Tor IPs and do analysis on just that data offline. Trying to actively do that filter in-path PLUS arbitrarily delay (ie queue in memory) that traffic in real time, all without signficantly affecting pass-through traffic seems like it would be a lot more expensive. Also, not to mention there is a limited number of bits that can be reliably encoded in this manner, and the purturbations of padding that shares the same TLS connection will lower this effectiveness. The adversary needs enough bits to get through to be able to track all the parties it is interested in. If padding is in place, it will have to spend considerable effort in redundancy to make sure that the timestamp remains present in the exit stream.. Which again means more queueing and more expense. Of course, it also means more expense on the part of the anonymity network in wasted bandwidth.. If padding slows down the network to the point where users start to leave, other, more dangerous effects take over. Finally, going on what has been disclosed so far in the EFF v AT&T case, it would seem that global adversary-style mass surveilance is in fact ocurring passively, out of path. At least the illegal domestic stuff, anyways. I suppose it's anyone's guess what they do when it's less blatantly illegal.. Maybe Echelon is the reason my bbc is so slow! :) -- Mike Perry Mad Computer Scientist fscked.org evil labs
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