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Add conditional assign and swap function for MPI modulus

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Signed-off-by: Gabor Mezei <gabor.mezei@arm.com>
This commit is contained in:
Gabor Mezei 2022-09-12 16:35:58 +02:00
parent e1d31c4aad
commit 12071d4403
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GPG key ID: F072ACA227ACD71D
2 changed files with 75 additions and 0 deletions
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18
library/bignum_mod_raw.c
View file

@ -41,6 +41,24 @@
#include "bignum_mod.h"
#include "constant_time_internal.h"
int mbedtls_mpi_mod_raw_cond_assign( mbedtls_mpi_uint *X,
mbedtls_mpi_uint *Y,
const mbedtls_mpi_mod_modulus *m,
unsigned char assign )
{
return mbedtls_mpi_core_cond_assign( X, m->limbs,
Y, m->limbs, assign );
}
int mbedtls_mpi_mod_raw_cond_swap( mbedtls_mpi_uint *X,
mbedtls_mpi_uint *Y,
const mbedtls_mpi_mod_modulus *m,
unsigned char swap )
{
return mbedtls_mpi_core_cond_swap( X, m->limbs,
Y, m->limbs, swap );
}
int mbedtls_mpi_mod_raw_read( mbedtls_mpi_uint *X,
const mbedtls_mpi_mod_modulus *m,
const unsigned char *input,

57
library/bignum_mod_raw.h
View file

@ -33,6 +33,63 @@
#include "bignum_mod.h"
/**
* \brief Perform a safe conditional copy of MPI which doesn't reveal whether
* the condition was true or not.
*
* \param[OUT] X The address of the first MPI. This must be initialized.
* \param[IN] Y The address of the second MPI. This must be initialized.
* \param[IN] m The address of the modulus related to \p X and \p Y.
* \param assign The condition deciding whether to perform the
* assignment or not. Must be either 0 or 1:
* * \c 1: Perform the assignment `X = Y`.
* * \c 0: Keep the original value of \p X.
*
* \note This function avoids leaking any information about whether
* the assignment was done or not.
*
* \warning If \p assign is neither 0 nor 1, the result of this function
* is indeterminate, and the resulting value in \p X might be
* neither its original value nor the value in \p Y.
*
* \return \c 0 if successful.
* \return #MBEDTLS_ERR_MPI_BUFFER_TOO_SMALL if \p X isn't
* large enough to hold the value in \p Y.
* \return #MBEDTLS_ERR_MPI_BAD_INPUT_DATA if \p X or \p Y is invalid.
*/
int mbedtls_mpi_mod_raw_cond_assign( mbedtls_mpi_uint *X,
mbedtls_mpi_uint *Y,
const mbedtls_mpi_mod_modulus *m,
unsigned char assign );
/**
* \brief Perform a safe conditional copy of MPI which doesn't reveal whether
* the condition was true or not.
*
* \param[IN,OUT] X The address of the first MPI. This must be initialized.
* \param[IN,OUT] Y The address of the second MPI. This must be initialized.
* \param[IN] m The address of the modulus related to \p X and \p Y.
* \param swap The condition deciding whether to perform
* the swap or not. Must be either 0 or 1:
* * \c 1: Swap the values of \p X and \p Y.
* * \c 0: Keep the original values of \p X and \p Y.
*
* \note This function avoids leaking any information about whether
* the swap was done or not.
*
* \warning If \p swap is neither 0 nor 1, the result of this function
* is indeterminate, and both \p X and \p Y might end up with
* values different to either of the original ones.
*
* \return \c 0 if successful.
* \return #MBEDTLS_ERR_MPI_BUFFER_TOO_SMALL if the size of
* \p X and \p Y is differ.
* \return #MBEDTLS_ERR_MPI_BAD_INPUT_DATA if \p X or \p Y is invalid.
*/int mbedtls_mpi_mod_raw_cond_swap( mbedtls_mpi_uint *X,
mbedtls_mpi_uint *Y,
const mbedtls_mpi_mod_modulus *m,
unsigned char swap );
/** Import X from unsigned binary data.
*
* The MPI needs to have enough limbs to store the full value (including any