On Thu, Nov 08, 2001 at 07:58:37PM -0000, [EMAIL PROTECTED] wrote: >The point is that it is >almost impossible to modify a binary image without changing the >MD5 checksum - in fact, to the best of my knowledge, this has not >been demonstrated, even in a laboratory environment - a very great >deal of trial and error would be required to match the 256 bit >checksum
First, MD5 is only a 128-bit checksum (SHA1, which is intended to replace it, is 160 bits). Second, there _are_ known weaknesses in MD5 -- as far as I remember, it is possible (although not without a great deal of work) to produce two messages/files with the same checksum -- but I don't think you can decide the checksum for yourself, and you certainly can't modify a file, add a few bytes and retain the checksum. Just that there are weaknesses, though (and they could be viewed as rather serious), would probably mean it's best to leave MD5 alone and instead use SHA1, which is (as far as I've heard -- I'm certainly no cryptography expert) extremely well-designed, and free from any known weaknesses. Except for the MD5 weakness, though, hashes are generally extremely difficult to fake -- that's their main purpose, after all :-) /* Steinar */ -- Homepage: http://www.sesse.net/ _________________________________________________________________________ Unsubscribe & list info -- http://www.ndatech.com/mersenne/signup.htm Mersenne Prime FAQ -- http://www.tasam.com/~lrwiman/FAQ-mers
