BN_bn2mpi
int BN_bn2mpi(const BIGNUM *a, unsigned char *to);
LCRYPTO_ALIAS(BN_bn2mpi);
LCRYPTO_USED(BN_bn2mpi);
if ((mpi_len = BN_bn2mpi(bn, NULL)) != bct->mpi_len) {
if ((mpi_len = BN_bn2mpi(bn, mpi_out)) != bct->mpi_len) {