Re: [hash2] Question about cryptographic guarantees of hash_append_unordered_range

From: Peter Dimov (pdimov_at_[hidden])
Date: 2024-12-08 21:19:41

Vinnie Falco wrote:
> On Sun, Dec 8, 2024 at 11:27 AM Ivan Matek via Boost
> <boost_at_[hidden]>
> wrote:
> 
> > ...sum is commutative.
> >
> 
> Bitwise XOR and modular unsigned multiplication are also commutative.

Bitwise xor has the problem that xoring two equal values yields 0, so
the sequences [1], [1, 1, 1], [1, 2, 2] and so on all hash to the same thing.

Multiply has the problem that a single 0 cancels out everything, and
the problem that multiplying 64 even numbers zeroes out the low
64 bits.