Re: [PATCH 1/4] lib/crypto: Add ML-DSA verification support

[David Howells]

Eric Biggers <ebiggers@xxxxxxxxxx> wrote:

> On Thu, Nov 20, 2025 at 01:55:18PM +0000, David Howells wrote:
> > Eric Biggers <ebiggers@xxxxxxxxxx> wrote:
> > 
> > > +	/* Compute d = (c mod 2^32) * (q^-1 mod 2^32). */
> > > +	s32 d = (s32)c * QINV_MOD_R;
> > 
> > Hmmm...  is "(s32)c" actually "(c mod 2^32)"?  Should that be:
> > 
> > 	u32 d = (u32)c * QINV_MOD_R;
> > 
> > This is followed up by casting 'd' to "s64".  I don't think that should
> > sign-extend it, but...
> 
> It selects the representative in the range [INT32_MIN, INT32_MAX],
> rather than the representative in the range [0, UINT32_MAX].  The sign
> extension is intentional.

I'm concerned about the basis on which it becomes positive or negative.  It
looks like the sign bit ends up being chosen arbitrarily.

> > > +		/* Reduce to [0, q), then tmp = w'_1 = UseHint(h, w'_Approx) */
> > 
> > Bracket mismatch.  "[0, q]"
> 
> It's intentional, since it denotes a mathematical range.  Elsewhere I
> used the words "the range" explicitly, so I'll add that above too.  (Or
> maybe reword it differently.)

I meant you have an opening square bracket and a closing round bracket in
"[0, q)".

David