David G. Andersen just mooed: > > What's the error rate when sending only the hash? Since the > probabilities are small, we can effectively add them. > > P(undetected TCP error) = 0.000000005 > P(hash collision) = 1/1208925819614629174706176 > =~ 0.00000000000000000000001 > > "Worsening" = 0.00000000500000000000001 (btw, I wasn't really being fair to compare-by-hash in this example. Assuming you're synchronizing a "moderate" file with rsync, it's going to split it into, say, S/1k chunks. So let's be nasty and say that it's a 1Tb file. The chances of any one block colliding with any of the other blocks in the file is (again, because our probabilities are really small) 2^30 / 2^160 =~ 1/2^130. In the example above, I used a very conservative value of 1/2^80. So the actual worsening is probably from 0.0000005 to 0.000000500000000000000000000000000000001 I'll take those odds any day. Even if you send each data packet 3x with a non-hashed rcp, your chances of death per-packet are still 0.000000000000000000125 or thereabouts... -Dave -- work: [email protected] me: [email protected] MIT Laboratory for Computer Science http://www.angio.net/ I do not accept unsolicited commercial email. Do not spam me. _______________________________________________ [email protected] mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-security To unsubscribe, send any mail to "[email protected]"