eden-emu/mbedtls
15
0
Fork 0
Code Issues Pull requests Projects Releases Packages Wiki Activity Actions

mbedtls_ecp_gen_privkey_sw: generalize to mbedtls_mpi_random

Browse source 
Rename mbedtls_ecp_gen_privkey_sw to mbedtls_mpi_random since it has
no particular connection to elliptic curves beyond the fact that its
operation is defined by the deterministic ECDSA specification. This is
a generic function that generates a random MPI between 1 inclusive and
N exclusive.

Slightly generalize the function to accept a different lower bound,
which adds a negligible amount of complexity.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
This commit is contained in:
Gilles Peskine 2021-03-29 21:53:58 +02:00
parent 7888073147
commit 8cfffb30b3
4 changed files with 119 additions and 99 deletions
Download patch file Download diff file Expand all files Collapse all files

27
library/ecp.c
View file

@ -3093,15 +3093,17 @@ cleanup:
#if defined(MBEDTLS_ECP_SHORT_WEIERSTRASS_ENABLED)
MBEDTLS_STATIC_TESTABLE
int mbedtls_ecp_gen_privkey_sw( const mbedtls_mpi *N, size_t n_bits,
mbedtls_mpi *d,
int (*f_rng)(void *, unsigned char *, size_t),
void *p_rng )
int mbedtls_mpi_random( mbedtls_mpi *X,
mbedtls_mpi_sint min,
const mbedtls_mpi *N,
int (*f_rng)(void *, unsigned char *, size_t),
void *p_rng )
{
/* SEC1 3.2.1: Generate d such that 1 <= n < N */
int ret = MBEDTLS_ERR_ECP_BAD_INPUT_DATA;
/* SEC1 3.2.1: Generate X such that 1 <= n < N */
int ret = MBEDTLS_ERR_MPI_BAD_INPUT_DATA;
int count = 0;
unsigned cmp = 0;
size_t n_bits = mbedtls_mpi_bitlen( N );
size_t n_bytes = ( n_bits + 7 ) / 8;
/*
@ -3114,8 +3116,8 @@ int mbedtls_ecp_gen_privkey_sw( const mbedtls_mpi *N, size_t n_bits,
*/
do
{
MBEDTLS_MPI_CHK( mbedtls_mpi_fill_random( d, n_bytes, f_rng, p_rng ) );
MBEDTLS_MPI_CHK( mbedtls_mpi_shift_r( d, 8 * n_bytes - n_bits ) );
MBEDTLS_MPI_CHK( mbedtls_mpi_fill_random( X, n_bytes, f_rng, p_rng ) );
MBEDTLS_MPI_CHK( mbedtls_mpi_shift_r( X, 8 * n_bytes - n_bits ) );
/*
* Each try has at worst a probability 1/2 of failing (the msb has
@ -3128,17 +3130,17 @@ int mbedtls_ecp_gen_privkey_sw( const mbedtls_mpi *N, size_t n_bits,
*/
if( ++count > 30 )
{
ret = MBEDTLS_ERR_ECP_RANDOM_FAILED;
ret = MBEDTLS_ERR_MPI_NOT_ACCEPTABLE;
goto cleanup;
}
ret = mbedtls_mpi_lt_mpi_ct( d, N, &cmp );
ret = mbedtls_mpi_lt_mpi_ct( X, N, &cmp );
if( ret != 0 )
{
goto cleanup;
}
}
while( mbedtls_mpi_cmp_int( d, 1 ) < 0 || cmp != 1 );
while( mbedtls_mpi_cmp_int( X, min ) < 0 || cmp != 1 );
cleanup:
return( ret );
@ -3164,8 +3166,7 @@ int mbedtls_ecp_gen_privkey( const mbedtls_ecp_group *grp,
#if defined(MBEDTLS_ECP_SHORT_WEIERSTRASS_ENABLED)
if( mbedtls_ecp_get_type( grp ) == MBEDTLS_ECP_TYPE_SHORT_WEIERSTRASS )
return( mbedtls_ecp_gen_privkey_sw( &grp->N, grp->nbits, d,
f_rng, p_rng ) );
return( mbedtls_mpi_random( d, 1, &grp->N, f_rng, p_rng ) );
#endif /* MBEDTLS_ECP_SHORT_WEIERSTRASS_ENABLED */
return( MBEDTLS_ERR_ECP_BAD_INPUT_DATA );