BN_bn2bin
(*var)->l = BN_bn2bin(bn, (unsigned char *) (*var)->v);
BN_bn2bin(in, (unsigned char *) binbuf->v);
BN_bn2bin(bn, (unsigned char *) binbuf);
binbuf[0] = BN_bn2bin(RSA_get0_e(key), (unsigned char *) &binbuf[1]);
ret = BN_bn2bin(RSA_get0_n(key), (unsigned char *) (&binbuf[binbuf[0] + 1]));
int BN_bn2bin(const BIGNUM */*a*/, unsigned char */*b*/);