Adjust mbedtls_mpi_mul_int() to changed signature of mpi_mul_hlp()
A previous commit has changed the signature of mpi_mul_hlp(), making
the length of the output explicit.
This commit adjusts mbedtls_mpi_mul_int() to this change.
Along the way, we make the code simpler and more secure by not calculating
the minimal limb-size of A. A previous comment indicated that this was
functionally necessary because of the implementation of mpi_mul_hlp() --
if it ever was, it isn't anymore.
Signed-off-by: Hanno Becker <hanno.becker@arm.com>
diff --git a/library/bignum.c b/library/bignum.c
index da8e8ca..91ba824 100644
--- a/library/bignum.c
+++ b/library/bignum.c
@@ -1525,17 +1525,9 @@
MPI_VALIDATE_RET( X != NULL );
MPI_VALIDATE_RET( A != NULL );
- /* mpi_mul_hlp can't deal with a leading 0. */
- size_t n = A->n;
- while( n > 0 && A->p[n - 1] == 0 )
- --n;
-
- /* The general method below doesn't work if n==0 or b==0. By chance
- * calculating the result is trivial in those cases. */
- if( b == 0 || n == 0 )
- {
+ /* The general method below doesn't work if b==0. */
+ if( b == 0 )
return( mbedtls_mpi_lset( X, 0 ) );
- }
/* Calculate A*b as A + A*(b-1) to take advantage of mpi_mul_hlp */
int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
@@ -1547,9 +1539,9 @@
* calls to calloc() in ECP code, presumably because it reuses the
* same mpi for a while and this way the mpi is more likely to directly
* grow to its final size. */
- MBEDTLS_MPI_CHK( mbedtls_mpi_grow( X, n + 1 ) );
+ MBEDTLS_MPI_CHK( mbedtls_mpi_grow( X, A->n + 1 ) );
MBEDTLS_MPI_CHK( mbedtls_mpi_copy( X, A ) );
- mpi_mul_hlp( n, A->p, X->p, b - 1 );
+ mpi_mul_hlp( X->p, X->n, A->p, A->n, b - 1 );
cleanup:
return( ret );