crypto_ecdh_encode_key
EXPORT_SYMBOL_GPL(crypto_ecdh_encode_key);
crypto_ecdh_encode_key(encoded_key, buf_len, &p);
int crypto_ecdh_encode_key(char *buf, unsigned int len, const struct ecdh *p);
err = crypto_ecdh_encode_key(buf, buf_len, &p);