Re: [Caml-list] Hashtbl and security

[Goswin von Brederlow <goswin-v-b@web.de>]

"Gerd Stolpmann" <info@gerd-stolpmann.de> writes:

> Well, looks like that the upper 32 bits aren't considered at all for
> computing the hash value. This is for sure surprising - I would have
> expected that these bits somehow go in to the final value (e.g. that they
> are xor-ed with the lower half).
>
> My guess is that this was done to ensure that an int-to-something
> hashtable can be marshalled from 64 to 32 bit systems. Not sure for what
> this is important, but it looks like a nice symmetry.

Marshaling hashtables of ints might be an argument. BUT:

# Hashtbl.hash (1 lsr 40);;
- : int = 0
# Hashtbl.hash (Int64.of_int (1 lsr 40));;
- : int = 0
# Hashtbl.hash (Int64.of_int (1 lsr 40 + 1));;
- : int = 1

> In trunk the method for ensuring this seems to have changed (see function
> caml_hash_mix_intnat in
> http://caml.inria.fr/cgi-bin/viewvc.cgi/ocaml/trunk/byterun/hash.c?revision=12072&view=markup).
>
> Gerd

Lets hope that fixes this.

MfG
        Goswin