GOST_le2bn
extern BIGNUM *GOST_le2bn(const unsigned char *buf, size_t len, BIGNUM *bn);
X = GOST_le2bn(octet->data, len, NULL);
Y = GOST_le2bn(octet->data + len, len, NULL);
pk_num = GOST_le2bn(s->data, s->length, NULL);
GOST_le2bn(sig, siglen / 2, s->r);
GOST_le2bn(sig + siglen / 2, siglen / 2, s->s);
md = GOST_le2bn(tbs, tbs_len, NULL);
md = GOST_le2bn(tbs, tbs_len, NULL);
GOST_le2bn(ukm, 8, UKM);