Re: Basic Question

Je 2006-10-20, soneill@[EMAIL PROTECTED]
 <soneill@[EMAIL PROTECTED]
> skribis:

> validator for that message.  I believe that an alogrithm like MD5, for
> example, which produces a 128-bit hash, is guaranteed not to produce any
> collisions for strings up to 2^64 bits in length.  If the messages
produced by
> your system are shorter than that, then the MD5 hash value accompanying
a
> message can almost certainly be accepted as the correct validator for
that
> message.

I'm afraid you're confusing two things.  Any 128-bit hash is guaranteed
to produce collisions for some strings no longer than 129 bits.  On the
other hand, if you pick substantially less than 2^64 different strings
at random, no matter what their lengths, then a good 128-bit hash is
unlikely to produce collisions among the strings.  The exact meaning of
"substantially less" can be calculated given the exact meaning of
"unlikely" and vice versa.

Taneli Huuskonen
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