New test helper mbedtls_test_read_mpi

This test helper reads an MPI from a string and guarantees control over the
number of limbs of the MPI, allowing test cases to construct values with or
without leading zeros, including 0 with 0 limbs.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
This commit is contained in:
Gilles Peskine 2021-06-11 14:13:53 +02:00
parent 23942a4b20
commit db4797198a
2 changed files with 40 additions and 0 deletions

View file

@ -54,6 +54,10 @@
#include <stddef.h>
#include <stdint.h>
#if defined(MBEDTLS_BIGNUM_C)
#include "mbedtls/bignum.h"
#endif
typedef enum
{
MBEDTLS_TEST_RESULT_SUCCESS = 0,
@ -294,4 +298,25 @@ void mbedtls_test_err_add_check( int high, int low,
const char *file, int line);
#endif
#if defined(MBEDTLS_BIGNUM_C)
/** Read an MPI from a string.
*
* Like mbedtls_mpi_read_string(), but size the resulting bignum based
* on the number of digits in the string. In particular, construct a
* bignum with 0 limbs for an empty string, and a bignum with leading 0
* limbs if the string has sufficiently many leading 0 digits.
*
* This is important so that the "0 (null)" and "0 (1 limb)" and
* "leading zeros" test cases do what they claim.
*
* \param[out] X The MPI object to populate. It must be initialized.
* \param radix The radix (2 to 16).
* \param[in] s The null-terminated string to read from.
*
* \return \c 0 on success, an \c MBEDTLS_ERR_MPI_xxx error code otherwise.
*/
/* Since the library has exactly the desired behavior, this is trivial. */
int mbedtls_test_read_mpi( mbedtls_mpi *X, int radix, const char *s );
#endif /* MBEDTLS_BIGNUM_C */
#endif /* TEST_HELPERS_H */

View file

@ -338,3 +338,18 @@ void mbedtls_test_err_add_check( int high, int low,
}
}
#endif /* MBEDTLS_TEST_HOOKS */
#if defined(MBEDTLS_BIGNUM_C)
int mbedtls_test_read_mpi( mbedtls_mpi *X, int radix, const char *s )
{
/* mbedtls_mpi_read_string() currently retains leading zeros.
* It always allocates at least one limb for the value 0. */
if( s[0] == 0 )
{
mbedtls_mpi_free( X );
return( 0 );
}
else
return( mbedtls_mpi_read_string( X, radix, s ) );
}
#endif