On Sat, May 05, 2012 at 01:47:45AM +0200, Ondrej Mikle wrote: > One trick I had in mind was create "secret hash function" (take the following > with a grain of salt, algebra is not my "primary thing"): > > - you keep generators g_i secret, which turns the problem from discrete-log > into > a problem of finding n-th root in finite field (n is the value of the digraph, > trigraph or few characters, e.g. encoded value of 'ec2bridge', possibly > "blinded" by another multiplication with secret constant c_i) > - in general, computing n-th root is quite slow [1], but there are many > special > cases like square root (quadratic residue) > - the above properties would make it slow for attacker to brute-force all > possible values - i.e. attacker can't just compute the result values of such > homomorphic hash, because he doesn't know the function parameters (e.g. > without > computing the generators), but everyone can use the "homomorphic property" for > testing parts
It sounds like you're talking about the homomorphic hashing paper you linked to in your last email. But there, the exponentiations are in Z_p, and taking n-th roots in Z_p is totally trivial. I seem to have lost the thread of why we're doing this. Is it just to count how many bridges are running our ec2 / rackspace / etc. bridge images? Can't we just report that out of band? Is the EC2 IP space not known? I must be missing something. - Ian _______________________________________________ tor-dev mailing list tor-dev@lists.torproject.org https://lists.torproject.org/cgi-bin/mailman/listinfo/tor-dev