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Split mbedtls_mpi_mod_inv() into separate functions for mont/non-mont form

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Signed-off-by: Tom Cosgrove <tom.cosgrove@arm.com>
This commit is contained in:
Tom Cosgrove 2022-12-13 11:57:57 +00:00
parent 4302d02fa8
commit a9e0f95903
1 changed files with 66 additions and 78 deletions
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144
library/bignum_mod.c
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@ -192,6 +192,54 @@ int mbedtls_mpi_mod_sub( mbedtls_mpi_mod_residue *X,
return( 0 );
}
static int mbedtls_mpi_mod_inv_mont( mbedtls_mpi_mod_residue *X,
const mbedtls_mpi_mod_residue *A,
const mbedtls_mpi_mod_modulus *N,
mbedtls_mpi_uint *working_memory )
{
/* Input already in Montgomery form, so there's little to do */
mbedtls_mpi_mod_raw_inv_prime( X->p, A->p,
N->p, N->limbs,
N->rep.mont.rr,
working_memory );
return( 0 );
}
static int mbedtls_mpi_mod_inv_non_mont( mbedtls_mpi_mod_residue *X,
const mbedtls_mpi_mod_residue *A,
const mbedtls_mpi_mod_modulus *N,
mbedtls_mpi_uint *working_memory )
{
/* Need to convert input into Montgomery form */
int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
mbedtls_mpi_mod_modulus Nmont;
mbedtls_mpi_mod_modulus_init( &Nmont );
MBEDTLS_MPI_CHK( mbedtls_mpi_mod_modulus_setup( &Nmont, N->p, N->limbs,
MBEDTLS_MPI_MOD_REP_MONTGOMERY ) );
/* We'll use X->p to hold the Montgomery form of the input A->p */
mbedtls_mpi_core_to_mont_rep( X->p, A->p, Nmont.p, Nmont.limbs,
Nmont.rep.mont.mm, Nmont.rep.mont.rr,
working_memory );
mbedtls_mpi_mod_raw_inv_prime( X->p, X->p,
Nmont.p, Nmont.limbs,
Nmont.rep.mont.rr,
working_memory );
/* And convert back from Montgomery form */
mbedtls_mpi_core_from_mont_rep( X->p, X->p, Nmont.p, Nmont.limbs,
Nmont.rep.mont.mm, working_memory );
cleanup:
mbedtls_mpi_mod_modulus_free( &Nmont );
return( ret );
}
int mbedtls_mpi_mod_inv( mbedtls_mpi_mod_residue *X,
const mbedtls_mpi_mod_residue *A,
const mbedtls_mpi_mod_modulus *N )
@ -203,94 +251,34 @@ int mbedtls_mpi_mod_inv( mbedtls_mpi_mod_residue *X,
if( mbedtls_mpi_core_check_zero_ct( A->p, A->limbs ) == 0 )
return( MBEDTLS_ERR_MPI_BAD_INPUT_DATA );
/* Will we need to do Montgomery conversion? */
int mont_conv_needed;
switch( N->int_rep )
{
case MBEDTLS_MPI_MOD_REP_MONTGOMERY:
mont_conv_needed = 0;
break;
case MBEDTLS_MPI_MOD_REP_OPT_RED:
mont_conv_needed = 1;
break;
default:
return( MBEDTLS_ERR_MPI_BAD_INPUT_DATA );
}
int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
/* If the input is already in Montgomery form, we have little to do but
* allocate working memory and call mbedtls_mpi_mod_raw_inv_prime().
*
* If it's not, we need to
* 1. Create a Montgomery version of the modulus;
* 2. Convert the input into Mont. form, using X->p to hold it;
* 3. (allocate and convert, same as if already in Mont. form);
* 4. Convert the inverted output back from Mont. form.
*
* Since the Montgomery conversion functions are in-place, we'll need to
* copy A into X before we start working on it (which could be avoided if
* there was a not-in-place function to convert to Montgomery form.
*/
/* Montgomery version of modulus (if not already in Mont. form).
* We will only call setup if the input is not already in Montgomery form.
* We will re-use N->p from input modulus, and make use of the fact that
* mbedtls_mpi_mod_raw_to_mont_rep() won't free it. */
mbedtls_mpi_mod_modulus Nmont;
mbedtls_mpi_mod_modulus_init( &Nmont );
size_t working_limbs =
mbedtls_mpi_mod_raw_inv_prime_working_limbs( N->limbs );
mbedtls_mpi_uint *working_memory = mbedtls_calloc( working_limbs,
sizeof(mbedtls_mpi_uint) );
if( working_memory == NULL )
return( MBEDTLS_ERR_MPI_ALLOC_FAILED );
int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
switch( N->int_rep )
{
ret = MBEDTLS_ERR_MPI_ALLOC_FAILED;
goto cleanup;
case MBEDTLS_MPI_MOD_REP_MONTGOMERY:
ret = mbedtls_mpi_mod_inv_mont( X, A, N, working_memory );
break;
case MBEDTLS_MPI_MOD_REP_OPT_RED:
ret = mbedtls_mpi_mod_inv_non_mont( X, A, N, working_memory );
break;
default:
ret = MBEDTLS_ERR_MPI_BAD_INPUT_DATA;
break;
}
const mbedtls_mpi_uint *to_invert; /* Will alias A->p or X->p */
const mbedtls_mpi_mod_modulus *Nuse; /* Which of N and Nmont to use */
mbedtls_platform_zeroize( working_memory,
working_limbs * sizeof(mbedtls_mpi_uint) );
free( working_memory );
if( mont_conv_needed )
{
MBEDTLS_MPI_CHK( mbedtls_mpi_mod_modulus_setup( &Nmont, N->p, N->limbs,
MBEDTLS_MPI_MOD_REP_MONTGOMERY ) );
mbedtls_mpi_core_to_mont_rep( X->p, A->p, Nmont.p, Nmont.limbs,
Nmont.rep.mont.mm, Nmont.rep.mont.rr,
working_memory );
to_invert = X->p;
Nuse = &Nmont;
}
else
{
to_invert = A->p;
Nuse = N;
}
mbedtls_mpi_mod_raw_inv_prime( X->p, to_invert,
Nuse->p, Nuse->limbs,
Nuse->rep.mont.rr,
working_memory );
if( mont_conv_needed )
mbedtls_mpi_core_from_mont_rep( X->p, X->p, Nmont.p, Nmont.limbs,
Nmont.rep.mont.mm, working_memory );
cleanup:
mbedtls_mpi_mod_modulus_free( &Nmont );
if (working_memory != NULL )
{
mbedtls_platform_zeroize( working_memory,
working_limbs * sizeof(mbedtls_mpi_uint) );
mbedtls_free( working_memory );
}
return( ret );
return ret;
}
/* END MERGE SLOT 3 */