-----BEGIN PGP SIGNED MESSAGE----- Subject: Re: rsync and md4 To: perry@piermont.com, ogren@cris.com Cc: markm@voicenet.com, Andrew.Tridgell@anu.edu.au, cypherpunks@toad.com
"David F. Ogren" writes:
Are you sure? MD5 is a 128 bit hash, and the probability of collision with a specific random piece of data (of any length) should be 2^-128. I could be wrong, but do you have any explanation of why you think the answer is 2^-64.
Does the phrase "birthday attack" mean anything to you?
But this isn't a birthday attack. Its a comparison between one specific file and one randomly chosen one.
MD4 is the fastest hash I am aware of. However, there has been some successful attacks against two rounds of MD4. Although this is not to suggest that MD4 is insecure, MD5 almost as fast (~1.3 times slower) and more secure.
I'm afraid you are totally wrong here. MD4 has been completely broken. I wouldn't trust it for anything. In fact, MD5 is no longer trustworthy, either -- it was broken recently. Stick to SHA.
Unless you are aware of some attack that I'm not, this is the most current information on MD4 and MD5: MD4 has had successful attacks on limited rounds. It has _not_ been completely cracked. MD5 has not been broken. A weakness has been shown, but collisions still cannot be developed. So checksums should still be secure. Additionally, in this case we are more concerned with the chance of random collisions than intentional collisions. In fact, I was probably wrong to suggest MD5. It _is_ more secure, but speed is his first priority, not security. SHA1 is a good hash algorithm as far as security goes (I've used it myself), but it's over three times slower than MD4. - -- David F. Ogren | ogren@concentric.net | "A man without religion is like a fish PGP Key ID: 0x6458EB29 | without a bicycle" - ------------------------------|---------------------------------------- Don't know what PGP is? | Need my public key? It's available Send a message to me with the | by server or by sending me a message subject GETPGPINFO | with the subject GETPGPKEY - -- David F. Ogren | ogren@concentric.net | "A man without religion is like a fish PGP Key ID: 0x6458EB29 | without a bicycle" - ------------------------------|---------------------------------------- Don't know what PGP is? | Need my public key? It's available Send a message to me with the | by server or by sending me a message subject GETPGPINFO | with the subject GETPGPKEY -----BEGIN PGP SIGNATURE----- Version: 2.6.2 iQEVAwUBMddOi+SLhCBkWOspAQHLTgf7BsDpCO2nhxsHYOunVv8abXWgITexhM/Z vmYWaz2Lgu3tBYZHXIG7B2ijTikZ7u8RgMGd9esipjFxOks1bHRQwYbVbWeDUDb3 O0c5TmPPmZt/7PscUEw1D3hhtj8HeGmn9pfu0y/I54OnMIJzbvNMICpMtLLDXJCu PhpUoAfamyRdWl9OYAvZ3LBMLBdGagzCh/jPxCQ9gEBq0aYMkxF1/qlfIMdmegow H/uL+TRgN5roTIKDZPGPZWYbdLbf0NT00avPz5qKaA5BkOpxYgeRKtoBHdYC5krH O2NZGZqb5LRKgxW9+IvCWoUoJQTB6IXP+YDU7p4pbn/Y/QORSHzqGA== =WA0Y -----END PGP SIGNATURE-----