commit b62bad442e6afc863829d130f3cb5e5b5bacdf61
author Janos Follath <janos.follath@arm.com> Thu Nov 24 16:48:41 2022 +0000
committer Janos Follath <janos.follath@arm.com> Fri Nov 25 17:55:00 2022 +0000
tree b8856c770cb26dd80ae77a26e8134cd0374e61e3
parent 8b375451c55600f32319771b3e36a3dce47b7881

Bidnum Mod: fix check in setup

We want to make sure that the value has at least as many limbs allocated
as the modulus as we need this to be able to do any operations in
constant time.

An invariant of the API is that the residue values are canonical, make
sure that the residue is compared to the entire modulus.

Signed-off-by: Janos Follath <janos.follath@arm.com>

library/bignum_mod.c

diff --git a/library/bignum_mod.c b/library/bignum_mod.c
index c10fb2e..1b3aff6 100644
--- a/library/bignum_mod.c
+++ b/library/bignum_mod.c
@@ -39,7 +39,7 @@
                                    mbedtls_mpi_uint *p,
                                    size_t p_limbs )
 {
-    if( p_limbs > m->limbs || !mbedtls_mpi_core_lt_ct( p, m->p, p_limbs ) )
+    if( p_limbs < m->limbs || !mbedtls_mpi_core_lt_ct( p, m->p, m->limbs ) )
         return( MBEDTLS_ERR_MPI_BAD_INPUT_DATA );
 
     r->limbs = m->limbs;