Function create_onionreply

common/sphinx.c:682–736

}

struct onionreply *create_onionreply(const tal_t *ctx,
				     const struct secret *shared_secret,
				     const u8 *failure_msg)
{
	size_t msglen = tal_count(failure_msg);
	size_t padlen = ONION_REPLY_SIZE - msglen;
	struct onionreply *reply = tal(ctx, struct onionreply);
	u8 *payload = tal_arr(ctx, u8, 0);
	struct secret key;
	struct hmac hmac;

	/* BOLT #4:
	 *
	 * The node generating the error message (_erring node_) builds a return
	 * packet consisting of
	 * the following fields:
	 *
	 * 1. data:
	 *    * [`32*byte`:`hmac`]
	 *    * [`u16`:`failure_len`]
	 *    * [`failure_len*byte`:`failuremsg`]
	 *    * [`u16`:`pad_len`]
	 *    * [`pad_len*byte`:`pad`]
	 */
	towire_u16(&payload, msglen);
	towire(&payload, failure_msg, msglen);
	towire_u16(&payload, padlen);
	towire_pad(&payload, padlen);

	/* BOLT #4:
	 *
	 * The _erring node_:
	 *   - SHOULD set `pad` such that the `failure_len` plus `pad_len` is
	 *     equal to 256.
	 *     - Note: this value is 118 bytes longer than the longest
	 *       currently-defined message.
	 */
	assert(tal_count(payload) == ONION_REPLY_SIZE + 4);

	/* BOLT #4:
	 *
 	 * Where `hmac` is an HMAC authenticating the remainder of the packet,
	 * with a key generated using the above process, with key type `um`
	 */
	subkey_from_hmac("um", shared_secret, &key);

	compute_hmac(&key, payload, tal_count(payload), NULL, 0, &hmac);
	reply->contents = tal_arr(reply, u8, 0),
	towire_hmac(&reply->contents, &hmac);

	towire(&reply->contents, payload, tal_count(payload));
	tal_free(payload);

	return reply;
}

struct onionreply *wrap_onionreply(const tal_t *ctx,
				   const struct secret *shared_secret,