[16069] in cryptography@c2.net mail archive
Re: "Approximate" hashes
daemon@ATHENA.MIT.EDU (Marcel Popescu)
Wed Sep 1 12:54:57 2004
X-Original-To: cryptography@metzdowd.com
X-Original-To: cryptography@metzdowd.com
From: "Marcel Popescu" <Marcel_Popescu@microbilt.com>
To: <cryptography@metzdowd.com>
Date: Wed, 1 Sep 2004 18:02:44 +0300
X-MDaemon-Deliver-To: cryptography@metzdowd.com
From: "Marcel Popescu" <Marcel_Popescu@microbilt.com>
> 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"?
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. Does
anyone know of a mail transformation which could upset it? Can anyone see a
way to "attack" this by letting a significantly different message collide on
the same hash? (I'm ignoring the recent discoveries - they're not that
practical, I'm only trying to fight spam, not the government.)
Thanks,
Marcel
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