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Merge pull request #6233 from tom-cosgrove-arm/issue-6226-core-mul

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Bignum: extract core_mul from the prototype
This commit is contained in:
Janos Follath
2023-04-04 13:36:22 +01:00
committed by GitHub
parent 219f978097 d62605126d
commit 13c73de6de
6 changed files with 127 additions and 9 deletions
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11
library/bignum.c
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@ -1136,7 +1136,8 @@ int mbedtls_mpi_mul_mpi(mbedtls_mpi *X, const mbedtls_mpi *A, const mbedtls_mpi
MPI_VALIDATE_RET(A != NULL);
MPI_VALIDATE_RET(B != NULL);
mbedtls_mpi_init(&TA); mbedtls_mpi_init(&TB);
mbedtls_mpi_init(&TA);
mbedtls_mpi_init(&TB);
if (X == A) {
MBEDTLS_MPI_CHK(mbedtls_mpi_copy(&TA, A)); A = &TA;
@ -1166,13 +1167,7 @@ int mbedtls_mpi_mul_mpi(mbedtls_mpi *X, const mbedtls_mpi *A, const mbedtls_mpi
MBEDTLS_MPI_CHK(mbedtls_mpi_grow(X, i + j));
MBEDTLS_MPI_CHK(mbedtls_mpi_lset(X, 0));
for (size_t k = 0; k < j; k++) {
/* We know that there cannot be any carry-out since we're
* iterating from bottom to top. */
(void) mbedtls_mpi_core_mla(X->p + k, i + 1,
A->p, i,
B->p[k]);
}
mbedtls_mpi_core_mul(X->p, A->p, i, B->p, j);
/* If the result is 0, we don't shortcut the operation, which reduces
* but does not eliminate side channels leaking the zero-ness. We do

11
library/bignum_core.c
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@ -448,6 +448,17 @@ mbedtls_mpi_uint mbedtls_mpi_core_mla(mbedtls_mpi_uint *d, size_t d_len,
return c;
}
void mbedtls_mpi_core_mul(mbedtls_mpi_uint *X,
const mbedtls_mpi_uint *A, size_t A_limbs,
const mbedtls_mpi_uint *B, size_t B_limbs)
{
memset(X, 0, (A_limbs + B_limbs) * ciL);
for (size_t i = 0; i < B_limbs; i++) {
(void) mbedtls_mpi_core_mla(X + i, A_limbs + 1, A, A_limbs, B[i]);
}
}
/*
* Fast Montgomery initialization (thanks to Tom St Denis).
*/

20
library/bignum_core.h
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@ -398,6 +398,26 @@ mbedtls_mpi_uint mbedtls_mpi_core_mla(mbedtls_mpi_uint *X, size_t X_limbs,
const mbedtls_mpi_uint *A, size_t A_limbs,
mbedtls_mpi_uint b);
/**
* \brief Perform a known-size multiplication
*
* \p X may not be aliased to any of the inputs for this function.
* \p A may be aliased to \p B.
*
* \param[out] X The pointer to the (little-endian) array to receive
* the product of \p A_limbs and \p B_limbs.
* This must be of length \p A_limbs + \p B_limbs.
* \param[in] A The pointer to the (little-endian) array
* representing the first factor.
* \param A_limbs The number of limbs in \p A.
* \param[in] B The pointer to the (little-endian) array
* representing the second factor.
* \param B_limbs The number of limbs in \p B.
*/
void mbedtls_mpi_core_mul(mbedtls_mpi_uint *X,
const mbedtls_mpi_uint *A, size_t A_limbs,
const mbedtls_mpi_uint *B, size_t B_limbs);
/**
* \brief Calculate initialisation value for fast Montgomery modular
* multiplication