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RSA: use constant-time modinv in deduce_crt()

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Signed-off-by: Manuel Pégourié-Gonnard <manuel.pegourie-gonnard@arm.com>
This commit is contained in:
Manuel Pégourié-Gonnard
2025-08-13 13:57:35 +02:00
parent 7dcfd73731
commit 630148e67f
3 changed files with 22 additions and 4 deletions
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6
library/bignum.c
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@@ -1924,9 +1924,9 @@ int mbedtls_mpi_random(mbedtls_mpi *X,
/*
* Modular inverse: X = A^-1 mod N with N odd (and A any range)
*/
static int mbedtls_mpi_inv_mod_odd(mbedtls_mpi *X,
const mbedtls_mpi *A,
const mbedtls_mpi *N)
int mbedtls_mpi_inv_mod_odd(mbedtls_mpi *X,
const mbedtls_mpi *A,
const mbedtls_mpi *N)
{
int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
mbedtls_mpi T, G;

18
library/bignum_internal.h
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@@ -80,4 +80,22 @@ int mbedtls_mpi_gcd_modinv_odd(mbedtls_mpi *G,
const mbedtls_mpi *A,
const mbedtls_mpi *N);
/**
* \brief Modular inverse: X = A^-1 mod N with N odd
*
* \param[out] X The inverse of \p A modulo \p N on success,
* indeterminate otherwise.
* \param[in] A The number to invert.
* \param[in] N The modulus. Must be odd and greater than 1.
*
* \return \c 0 if successful.
* \return #MBEDTLS_ERR_MPI_ALLOC_FAILED if a memory allocation failed.
* \return #MBEDTLS_ERR_MPI_BAD_INPUT_DATA if preconditions were not
* met.
* \return #MBEDTLS_ERR_MPI_NOT_ACCEPTABLE if A is not invertible mod N.
*/
int mbedtls_mpi_inv_mod_odd(mbedtls_mpi *X,
const mbedtls_mpi *A,
const mbedtls_mpi *N);
#endif /* bignum_internal.h */

2
library/rsa_alt_helpers.c
View File

@@ -245,7 +245,7 @@ int mbedtls_rsa_deduce_crt(const mbedtls_mpi *P, const mbedtls_mpi *Q,
/* QP = Q^{-1} mod P */
if (QP != NULL) {
MBEDTLS_MPI_CHK(mbedtls_mpi_inv_mod(QP, Q, P));
MBEDTLS_MPI_CHK(mbedtls_mpi_inv_mod_odd(QP, Q, P));
}
cleanup: