Re: Formal review request for Hash2

From: Peter Dimov (pdimov_at_[hidden])
Date: 2024-12-05 00:27:41

Robert Ramey wrote:
> On 12/4/24 2:15 AM, Peter Dimov via Boost wrote:
> 
> > unequal
> > arguments should produce different hash values.
> >
> > Since the arguments above are distinct (with respect to operator==),
> > they should produce distinct hash values.
> >
> 
> What does "should" mean here?  How could you possible make such a
> guarentee.

For a high quality hash function, the formal meaning of "should" is
that the probability for a collision must be 2^-n, where n is the number
of bits of the hash value. (That is, the hash values should be uniformly
distributed.)

For a cryptographic hash function, the formal meaning of "should" is
that engineering a collision should be "computationally infeasible".