Re: [Caml-list] Hashtbl and security

[oliver <oliver@first.in-berlin.de>]

On Fri, Dec 30, 2011 at 06:06:26PM +0100, Xavier Leroy wrote:
> On 12/30/2011 05:44 PM, Gerd Stolpmann wrote:
> 
> > 1) Avoid hash tables in contexts where security is relevant. The
> > alternative is Set (actually a balanced binary tree), which does not
> > show this problem.
> 
> Highly recommended.  Nothing beats guaranteed O(log n) operations.
> 
> > 2) Use cryptographically secure hash functions.
> 
> Hopeless: with a hash size of 30 bits, as in Caml, or even 64 bits,
> there are no cryptographically secure hash functions.
> 
> > 3) Use "randomized" hash tables. The trick here is that there is not a
> > single hash function h anymore, but a family h(1)...h(n). When the hash
> > table is created, one of the functions is picked randomly. This makes it
> > impossible to craft an attack request, because you cannot predict the
> > function. 
> 
> Indeed.  The optional "seed" parameter to Hashtbl.create does exactly
> this in the new implementation of Hashtbl (the one based on Murmur3).
[...]


Where is this?

I found  Hashtbl.HashedType.hash  with type t -> int.

But I did not found an optional parameter to Hashtbl.create

Maybe that is part of the next release?

Ciao,
   Oliver