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Clean up initialization in _core_exp_mod()

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Signed-off-by: Janos Follath <janos.follath@arm.com>
This commit is contained in:
Janos Follath 2024-08-20 10:41:55 +01:00
parent 8786dd79f7
commit afb2079652
1 changed files with 15 additions and 5 deletions
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20
library/bignum_core.c
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@ -765,11 +765,21 @@ static inline void exp_mod_calc_first_bit_optionally_safe(const mbedtls_mpi_uint
size_t *E_bit_index) size_t *E_bit_index)
{ {
if (E_public == MBEDTLS_MPI_IS_PUBLIC) { if (E_public == MBEDTLS_MPI_IS_PUBLIC) {
/*
* Skip leading zero bits.
*/
size_t E_bits = mbedtls_mpi_core_bitlen(E, E_limbs); size_t E_bits = mbedtls_mpi_core_bitlen(E, E_limbs);
if (E_bits != 0) { if (E_bits == 0) {
*E_limb_index = E_bits / biL; /*
*E_bit_index = E_bits % biL; * If E is 0 mbedtls_mpi_core_bitlen() returns 0. Even if that is the case, we will want
* to represent it as a single 0 bit and as such the bitlength will be 1.
*/
E_bits = 1;
} }
*E_limb_index = E_bits / biL;
*E_bit_index = E_bits % biL;
#if defined(MBEDTLS_TEST_HOOKS) && !defined(MBEDTLS_THREADING_C) #if defined(MBEDTLS_TEST_HOOKS) && !defined(MBEDTLS_THREADING_C)
mbedtls_mpi_optionally_safe_codepath = MBEDTLS_MPI_IS_PUBLIC; mbedtls_mpi_optionally_safe_codepath = MBEDTLS_MPI_IS_PUBLIC;
#endif #endif
@ -847,8 +857,8 @@ static void mbedtls_mpi_core_exp_mod_optionally_safe(mbedtls_mpi_uint *X,
/* We'll process the bits of E from most significant /* We'll process the bits of E from most significant
* (limb_index=E_limbs-1, E_bit_index=biL-1) to least significant * (limb_index=E_limbs-1, E_bit_index=biL-1) to least significant
* (limb_index=0, E_bit_index=0). */ * (limb_index=0, E_bit_index=0). */
size_t E_limb_index = E_limbs; size_t E_limb_index;
size_t E_bit_index = 0; size_t E_bit_index;
exp_mod_calc_first_bit_optionally_safe(E, E_limbs, E_public, exp_mod_calc_first_bit_optionally_safe(E, E_limbs, E_public,
&E_limb_index, &E_bit_index); &E_limb_index, &E_bit_index);