At 06:02 PM 9/1/04 +0300, Marcel Popescu wrote: >From: "Marcel Popescu" <[EMAIL PROTECTED]> > >> Hence my question: is there some "approximate" hash function (which I >could >> use instead of SHA-1) which can verify that a text hashes "very close" to >a >> value? So that if I change, say, tabs into spaces, I won't get exactly the >> same value, but I would get a "good enough"?
This is completely what secure hashes are supposed to prevent. *Any* change in the input will flip half the hash-bits on average. Just like a block cipher. There is no input "nearness" preservation. That's part of the point of the algorithm. >I just had an idea. Would this work? > >- let S be the input string, whose hash I want to verify >- make S uppercase >- remove everything but A-Z, 0-9, and common punctuation (!;:'",.?) >- calculate the SHA1 hash of the result > >This should keep any insignificant changes out of the final result. You can encode your message in some format which is not subject to mangling, and use a hash of that encoding. You can then decode the encoding back into unicode or whatever funky but net-fragile character set you like. This is somewhat like ascii-armoring of PGP-encrypted messages. ================================================= 36 Laurelwood Dr Irvine CA 92620-1299 VOX: (714) 544-9727 (home) mnemonic: P1G JIG WRAP ICBM: -117.7621, 33.7275 HTTP: http://68.5.216.23:81 (back up, but not 99.999% reliable) PGP PUBLIC KEY: by arrangement Send plain ASCII text not HTML lest ye be misquoted ------ "Don't 'sir' me, young man, you have no idea who you're dealing with" Tommy Lee Jones, MIB ---- No, you're not 'tripping', that is an emu ---Hank R. Hill --------------------------------------------------------------------- The Cryptography Mailing List Unsubscribe by sending "unsubscribe cryptography" to [EMAIL PROTECTED]