I want to give a hint for those working till now in the problem of estimating the probability of A=B under the condition of hash(A)=hash(B).
Just suppose that hash is any function from a set X to Y, first suppose that X is finite (but very big), and that the probability to pick any element is the same (uniform). Y also finite (but not so big). A and B are supposed to be elements of X. But well, so much definition was not necessary: we know from where we have the problem, from the algorithm of rsync. And this problem is realy trivial. A little more complicated is to see the probability that rsync finds different A and B with hash(A)=hash(B), and hence with very high probability gives a false result. rsync divide the file in the client in m_1 (disjunct) blocks, the file in the server in m_2 blocks, and try to find blocks in the server with similar hash as blocks in the client. As said before, this is strongly dependent on the way the hash function maps X to Y. You may first suppose that it does it uniformly and calculate the probability that rsync does not find the collission. Rodrigo. Jan Stary <h...@stare.cz> wrote: > On Sep 18 21:59:08, hru...@gmail.com wrote: > > What was the probability? > > Motherfucking troll, you have been given the answer > like five times already. now get the fuck OFF. > > > Rodrigo. > > > > > > Eric Furman <ericfur...@fastmail.net> wrote: > > > > > Troll, the question has been answered. > > > You are an entertaining troll, though. > > > It is highly amusing seeing someone make themselves look so silly. > > > > > > On Tue, Sep 17, 2013, at 11:28 AM, hru...@gmail.com wrote: > > > > Marc Espie <es...@nerim.net> wrote: > > > > > > > > > > You have strings A and B, and you know only that hash(A)=hash(B): > > > > > > what > > > > > > is the probability that A=B? 2^-160? > > > > > > > > > > No, that's never the problem. > > > > > > > > > > You have a *given* string A, and another string B. > > > > > > > > O.K. You have string A in the client with hash(A)=n. You find string > > > > B in the server also with hash(B)=n. What is the probability that > > > > A=B? > > > > > > > > Rodrigo.
