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Adjust mbedtls_mpi_mul_int() to changed signature of mpi_mul_hlp()

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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>
This commit is contained in:
Hanno Becker
2022-04-06 06:27:00 +01:00
parent fee261a505
commit 74a11a31cb
1 changed files with 4 additions and 12 deletions
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16
library/bignum.c
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@@ -1525,17 +1525,9 @@ int mbedtls_mpi_mul_int( mbedtls_mpi *X, const mbedtls_mpi *A, mbedtls_mpi_uint
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 @@ int mbedtls_mpi_mul_int( mbedtls_mpi *X, const mbedtls_mpi *A, mbedtls_mpi_uint
* 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 );