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author | Tom Cosgrove <tom.cosgrove@arm.com> | 2022-12-06 10:46:30 +0000 |
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committer | Tom Cosgrove <tom.cosgrove@arm.com> | 2022-12-06 10:46:30 +0000 |
commit | ecda1868934796d0f423feaceadc07ce360f3bd3 (patch) | |
tree | 6f66cffb94a0d12d06176023733ce51bb30bac85 | |
parent | c3902ac6614c12133393be38ca21c7fb9e059812 (diff) | |
download | mbedtls-ecda1868934796d0f423feaceadc07ce360f3bd3.tar.gz |
Require input to mbedtls_mpi_core_exp_mod() to already be in Montgomery form
Signed-off-by: Tom Cosgrove <tom.cosgrove@arm.com>
-rw-r--r-- | library/bignum_core.c | 10 | ||||
-rw-r--r-- | library/bignum_core.h | 3 | ||||
-rw-r--r-- | scripts/mbedtls_dev/bignum_core.py | 15 |
3 files changed, 19 insertions, 9 deletions
diff --git a/library/bignum_core.c b/library/bignum_core.c index 663535107..2ed907da3 100644 --- a/library/bignum_core.c +++ b/library/bignum_core.c @@ -610,9 +610,9 @@ static void exp_mod_precompute_window( const mbedtls_mpi_uint *A, Wtable[0] = 1; mbedtls_mpi_core_montmul( Wtable, Wtable, RR, AN_limbs, N, AN_limbs, mm, temp ); - /* W[1] = A * R^2 * R^-1 mod N = A * R mod N */ + /* W[1] = A (already in Montgomery presentation) */ mbedtls_mpi_uint *W1 = Wtable + AN_limbs; - mbedtls_mpi_core_montmul( W1, A, RR, AN_limbs, N, AN_limbs, mm, temp ); + memcpy( W1, A, AN_limbs * ciL ); /* W[i+1] = W[i] * W[1], i >= 2 */ mbedtls_mpi_uint *Wprev = W1; @@ -626,6 +626,8 @@ static void exp_mod_precompute_window( const mbedtls_mpi_uint *A, /* Exponentiation: X := A^E mod N. * + * A must already be in Montgomery form. + * * As in other bignum functions, assume that AN_limbs and E_limbs are nonzero. * * RR must contain 2^{2*biL} mod N. @@ -730,10 +732,6 @@ int mbedtls_mpi_core_exp_mod( mbedtls_mpi_uint *X, } while( ! ( E_bit_index == 0 && E_limb_index == 0 ) ); - /* Convert X back to normal presentation */ - const mbedtls_mpi_uint one = 1; - mbedtls_mpi_core_montmul( X, X, &one, 1, N, AN_limbs, mm, temp ); - mbedtls_platform_zeroize( mempool, total_limbs * sizeof(mbedtls_mpi_uint) ); mbedtls_free( mempool ); return( 0 ); diff --git a/library/bignum_core.h b/library/bignum_core.h index 24559c6e9..334856456 100644 --- a/library/bignum_core.h +++ b/library/bignum_core.h @@ -500,11 +500,12 @@ int mbedtls_mpi_core_fill_random( mbedtls_mpi_uint *X, size_t X_limbs, /** * \brief Perform a modular exponentiation with secret exponent: - * X = A^E mod N + * X = A^E mod N, where \p A is already in Montgomery form. * * \param[out] X The destination MPI, as a little endian array of length * \p AN_limbs. * \param[in] A The base MPI, as a little endian array of length \p AN_limbs. + * Must be in Montgomery form. * \param[in] N The modulus, as a little endian array of length \p AN_limbs. * \param AN_limbs The number of limbs in \p X, \p A, \p N, \p RR. * \param[in] E The exponent, as a little endian array of length \p E_limbs. diff --git a/scripts/mbedtls_dev/bignum_core.py b/scripts/mbedtls_dev/bignum_core.py index 2960d242d..a000bde07 100644 --- a/scripts/mbedtls_dev/bignum_core.py +++ b/scripts/mbedtls_dev/bignum_core.py @@ -759,12 +759,23 @@ class BignumCoreExpMod(BignumCoreTarget, bignum_common.ModOperationCommon): """Test cases for bignum core exponentiation.""" symbol = "^" test_function = "mpi_core_exp_mod" - test_name = "Core modular exponentiation" + test_name = "Core modular exponentiation (Mongtomery form only)" input_style = "fixed" + def arguments(self) -> List[str]: + # Input 'a' has to be given in Montgomery form + mont_a = (self.int_a * self.r) % self.int_n + arg_mont_a = self.format_arg('{:x}'.format(mont_a)) + return [bignum_common.quote_str(n) for n in [self.arg_n, + arg_mont_a, + self.arg_b] + ] + self.result() + def result(self) -> List[str]: + # Result has to be given in Montgomery form result = pow(self.int_a, self.int_b, self.int_n) - return [self.format_result(result)] + mont_result = (result * self.r) % self.int_n + return [self.format_result(mont_result)] @property def is_valid(self) -> bool: |