int dslink_handshake_get_group(mbedtls_ecp_group *grp) {
mbedtls_ecp_group_init(grp);
const mbedtls_ecp_curve_info *info
= mbedtls_ecp_curve_info_from_grp_id(MBEDTLS_ECP_DP_SECP256R1);
if (!info) {
return DSLINK_CRYPT_MISSING_CURVE;
}
if ((errno = mbedtls_ecp_group_load(grp, info->grp_id)) != 0) {
return DSLINK_CRYPT_GROUP_LOAD_ERR;
}
return 0;
}
/*
* Parse a SpecifiedECDomain (SEC 1 C.2) and find the associated group ID
*/
static int pk_group_id_from_specified( const mbedtls_asn1_buf *params,
mbedtls_ecp_group_id *grp_id )
{
int ret;
mbedtls_ecp_group grp;
mbedtls_ecp_group_init( &grp );
if( ( ret = pk_group_from_specified( params, &grp ) ) != 0 )
goto cleanup;
ret = pk_group_id_from_group( &grp, grp_id );
cleanup:
mbedtls_ecp_group_free( &grp );
return( ret );
}
/*
* Find the group id associated with an (almost filled) group as generated by
* pk_group_from_specified(), or return an error if unknown.
*/
static int pk_group_id_from_group( const mbedtls_ecp_group *grp, mbedtls_ecp_group_id *grp_id )
{
int ret = 0;
mbedtls_ecp_group ref;
const mbedtls_ecp_group_id *id;
mbedtls_ecp_group_init( &ref );
for( id = mbedtls_ecp_grp_id_list(); *id != MBEDTLS_ECP_DP_NONE; id++ )
{
/* Load the group associated to that id */
mbedtls_ecp_group_free( &ref );
MBEDTLS_MPI_CHK( mbedtls_ecp_group_load( &ref, *id ) );
/* Compare to the group we were given, starting with easy tests */
if( grp->pbits == ref.pbits && grp->nbits == ref.nbits &&
mbedtls_mpi_cmp_mpi( &grp->P, &ref.P ) == 0 &&
mbedtls_mpi_cmp_mpi( &grp->A, &ref.A ) == 0 &&
mbedtls_mpi_cmp_mpi( &grp->B, &ref.B ) == 0 &&
mbedtls_mpi_cmp_mpi( &grp->N, &ref.N ) == 0 &&
mbedtls_mpi_cmp_mpi( &grp->G.X, &ref.G.X ) == 0 &&
mbedtls_mpi_cmp_mpi( &grp->G.Z, &ref.G.Z ) == 0 &&
/* For Y we may only know the parity bit, so compare only that */
mbedtls_mpi_get_bit( &grp->G.Y, 0 ) == mbedtls_mpi_get_bit( &ref.G.Y, 0 ) )
{
break;
}
}
cleanup:
mbedtls_ecp_group_free( &ref );
*grp_id = *id;
if( ret == 0 && *id == MBEDTLS_ECP_DP_NONE )
ret = MBEDTLS_ERR_ECP_FEATURE_UNAVAILABLE;
return( ret );
}