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Document and test aliasing of output for mbedtls_mpi_core_montmul()

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Signed-off-by: Tom Cosgrove <tom.cosgrove@arm.com>
This commit is contained in:
Tom Cosgrove 2022-09-20 13:17:51 +01:00
parent f2b3818a69
commit ea45c1d2d4
2 changed files with 35 additions and 0 deletions
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8
library/bignum_core.h
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@ -245,6 +245,14 @@ mbedtls_mpi_uint mbedtls_mpi_core_montmul_init( const mbedtls_mpi_uint *N );
/**
* \brief Montgomery multiplication: X = A * B * R^-1 mod N (HAC 14.36)
*
* \p X may be aliased to \p A or \p N, or even \p B (if \p AN_limbs ==
* \p B_limbs) but may not overlap any parameters otherwise.
*
* \p A, \p B and \p N must not alias or overlap each other in any way, even
* if \p AN_limbs == \p B_limbs.
*
* \p A and \p B must be in canonical form: that is, <= \p N.
*
* \param[out] X The destination MPI, as a little-endian array of
* length \p AN_limbs.
* On successful completion, X contains the result of

27
tests/suites/test_suite_mpi.function
View File

@ -2114,6 +2114,33 @@ void mpi_core_montmul( int limbs_AN4, int limbs_B4,
size_t bytes = N.n * sizeof(mbedtls_mpi_uint);
ASSERT_COMPARE( R.p, bytes, X->p, bytes );
/* The output (R, above) may be aliased to A - use R to save the value of A */
memcpy( R.p, A.p, bytes );
mbedtls_mpi_core_montmul( A.p, A.p, B.p, B.n, N.p, N.n, mm, T.p );
ASSERT_COMPARE( A.p, bytes, X->p, bytes );
memcpy( A.p, R.p, bytes ); /* restore A */
/* The output may be aliased to N - use R to save the value of N */
memcpy( R.p, N.p, bytes );
mbedtls_mpi_core_montmul( N.p, A.p, B.p, B.n, N.p, N.n, mm, T.p );
ASSERT_COMPARE( N.p, bytes, X->p, bytes );
memcpy( N.p, R.p, bytes );
/* The output may even be aliased to B, if AN_limbs == B_limbs */
if (limbs_AN == limbs_B)
{
/* Note: last test, so we don't save B */
mbedtls_mpi_core_montmul( B.p, A.p, B.p, B.n, N.p, N.n, mm, T.p );
ASSERT_COMPARE( B.p, bytes, X->p, bytes );
}
exit:
mbedtls_mpi_free( &A );
mbedtls_mpi_free( &B );