Re: [hash2] Review of Hash2

From: Antony Polukhin (antoshkka_at_[hidden])
Date: 2024-12-16 17:25:03

On Fri, Dec 13, 2024, 19:55 Peter Dimov via Boost <boost_at_[hidden]>
wrote:

> Antony Polukhin wrote:
> > CONDITIONAL ACCEPT. The behavior of the default constructor must be
> > secure.
>
> Hi Antony, thanks for the review.
>
> I of course agree that HashDOS is a problem. The library documentation
> points this out in several places, that's why SipHash is included and
> almost no other non-crypto hashes are, and its use is recommended.
>
> However, I don't agree that the default constructor of the hash algorithm
> _concept_ is the correct place to attempt to make things secure (or in
> practice, less insecure than before.)
>
> First, this would place the responsibility on hash algorithm authors, which
> doesn't seem correct, or reliable.
>
> Second, hash algorithms aren't only used in hash tables, and injecting
> nondeterminism in their default constructors seems user-hostile. The hash
> algorithm adaptor, once it's supplied by the library, would be a better
> place
> to do that, if we decide to do it.
>

After Vinnie's comment I've realised my source of confusion. Boost.Hash
library is about hashing for unordered containers, but Boost.Hash2 is about
hashing algorithms. Hash2 is not a replacement for Boost.Hash, it has
different goals.

Does it make sense to change the library name to highlight that?
Boost.HashAlgorithms? Or there is a plan to go further and provide adapters
for hash algorithms usage with unordered containers?

Third, using a single process-wide seed is not good practice (as you
> yourself
> observe.) It makes things more secure compared to unseeded use, but not
> really secure. The correct approach is to use a random seed (preferably of
> size 192 bits or more) that varies per connection, or per container.
>

Those 192 bits seem to be related to a particular hashing algorithm. Looks
like it makes sense for the hashing algorithm implementor to provide some
information on seed length. Is there any plan to get that information from
algorithm?

>