i2d_X509_PUBKEY
z = i2d_X509_PUBKEY(X509_get_X509_PUBKEY(x), &d);
ret = i2d_X509_PUBKEY(xpk, out);
der_len = i2d_X509_PUBKEY(pkey, &der);
int i2d_X509_PUBKEY(X509_PUBKEY *a, unsigned char **out);