Re: Hashing a procedure object reliably

On 13/04/2025 19:47, [email protected] wrote:
> On Sun, Apr 13, 2025 at 07:03:56PM +0200, Maxime Devos wrote:
>
> [...]
>
>>> Typical hashing of the non-cryptographic kind aren't designed to
>>> virtually eliminate hash collisions [...]
> Nit: given a "reasonable" hash, the collision probability should be
> the same for crypto or non-crypto hash (for the same width, for "random"
> input). [...]

Many hashes aren't reasonable, then.When looking at documents describing 
the quality of (non-crypto) string hash functions, you can sometimes see 
discussion about how certain hash values are unreachable and how to 
choose parameters such that hashes are more 'spread out' (and hence, 
making collisions less common), trade-offs between speed of hashing and 
risk of collision ...

For a simple (non-string) example, consider e.g. a situation where a 
hash in [0, M] is available, but you need a hash in range [0,N] where 
'N<M'. Doing 'old hash % N' brings it in the correct range, but can 
often seriously increase the risk of collisions in a way that cannot 
solely be accounted for by the decrease in range (specifics depend on 
the distribution of the initial hash function, and relation between N 
and M).

Best regards, Maxime Devos