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Bignum core: random: prepare to break out the core function

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Shuffle things around a bit inside mbedtls_mpi_random() in preparation for
breaking out mbedtls_mpi_core_random().

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
This commit is contained in:
Gilles Peskine 2022-09-21 13:43:30 +02:00
parent 8a32a75aa2
commit 26be89b3f6
1 changed files with 14 additions and 12 deletions
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26
library/bignum.c
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@ -1966,17 +1966,24 @@ int mbedtls_mpi_random( mbedtls_mpi *X,
int (*f_rng)(void *, unsigned char *, size_t),
void *p_rng )
{
int ret = MBEDTLS_ERR_MPI_BAD_INPUT_DATA;
int count;
unsigned ge_lower = 1, lt_upper = 0;
size_t n_bits = mbedtls_mpi_bitlen( N );
size_t n_bytes = ( n_bits + 7 ) / 8;
if( min < 0 )
return( MBEDTLS_ERR_MPI_BAD_INPUT_DATA );
if( mbedtls_mpi_cmp_int( N, min ) <= 0 )
return( MBEDTLS_ERR_MPI_BAD_INPUT_DATA );
/* Ensure that target MPI has exactly the same number of limbs
* as the upper bound, even if the upper bound has leading zeros.
* This is necessary for the mbedtls_mpi_lt_mpi_ct() check. */
int ret = mbedtls_mpi_resize_clear( X, N->n );
if( ret != 0 )
return( ret );
unsigned ge_lower = 1, lt_upper = 0;
size_t n_bits = mbedtls_mpi_bitlen( N );
size_t n_bytes = ( n_bits + 7 ) / 8;
ret = MBEDTLS_ERR_MPI_BAD_INPUT_DATA;
/*
* When min == 0, each try has at worst a probability 1/2 of failing
* (the msb has a probability 1/2 of being 0, and then the result will
@ -1994,12 +2001,7 @@ int mbedtls_mpi_random( mbedtls_mpi *X,
* is small, use a higher repeat count, otherwise the probability of
* failure is macroscopic.
*/
count = ( n_bytes > 4 ? 30 : 250 );
/* Ensure that target MPI has exactly the same number of limbs
* as the upper bound, even if the upper bound has leading zeros.
* This is necessary for the mbedtls_mpi_lt_mpi_ct() check. */
MBEDTLS_MPI_CHK( mbedtls_mpi_resize_clear( X, N->n ) );
int count = ( n_bytes > 4 ? 30 : 250 );
/*
* Match the procedure given in RFC 6979 §3.3 (deterministic ECDSA)