North American Network Operators Group Date Prev | Date Next | Date Index | Thread Index | Author Index | Historical Re: Senator Diane Feinstein Wants to know about the Benefits ofP2P
On Mon, 30 Aug 2004 14:33:21 -0700 (PDT), Gregory Hicks <[email protected]> writes: >> I recall even seeing posts about people claiming this meant original data >> being reconstructed from the checksum! That would be truly amazing since I >> could reconstruct a 680MB ISO from just 61d38fad42b4037970338636b5e72e5a. Wow! Assuming that MD5 is a PRF, about 2^{-128} files will have such a hash value. For a file 680MB in size, About 2^{680*1024*1024*8-128} in total. If I had a list of all of those files, it would be impossible for me to identify which of them was the 'right' image. First-preimage resistance means that it should be computationally infeasible for anyone to create *any* file with that particular hash. It was also believed to be computationally infeasible to find *any* two files that had the same MD5 hash. The attack on MD5 showed that it in fact is computationally feasible to find two files with the same MD5 --- someone did it. This attack showed that MD5 no longer meets some of its design requirements. > The "collision" problem discovered means that there might be > MULTIPLE 680MB files that give the same checksum. Scott
|