sphinx: Using hop_data to serialize per-hop information into onion

Signed-off-by: Christian Decker <decker.christian@gmail.com>

lightningd/sphinx.c

@@ -330,9 +330,35 @@ static struct hop_params *generate_hop_params(
 	return params;
 }
 
+static void serialize_hop_data(tal_t *ctx, u8 *dst, const struct hop_data *data)
+{
+	u8 *buf = tal_arr(ctx, u8, 0);
+	towire_u8(&buf, data->realm);
+	towire_short_channel_id(&buf, &data->channel_id);
+	towire_u32(&buf, data->amt_forward);
+	towire_u32(&buf, data->outgoing_cltv);
+	towire_pad(&buf, 16);
+	towire(&buf, data->hmac, SECURITY_PARAMETER);
+	memcpy(dst, buf, tal_len(buf));
+	tal_free(buf);
+}
+
+static void deserialize_hop_data(struct hop_data *data, const u8 *src)
+{
+	const u8 *cursor = src;
+	size_t max = HOP_DATA_SIZE;
+	data->realm = fromwire_u8(&cursor, &max);
+	fromwire_short_channel_id(&cursor, &max, &data->channel_id);
+	data->amt_forward = fromwire_u32(&cursor, &max);
+	data->outgoing_cltv = fromwire_u32(&cursor, &max);
+	fromwire_pad(&cursor, &max, 16);
+	fromwire(&cursor, &max, &data->hmac, SECURITY_PARAMETER);
+}
+
 struct onionpacket *create_onionpacket(
 	const tal_t *ctx,
 	struct pubkey *path,
+	struct hop_data hops_data[],
 	const u8 *sessionkey,
 	const u8 *assocdata,
 	const size_t assocdatalen
@@ -340,7 +366,7 @@ struct onionpacket *create_onionpacket(
 {
 	struct onionpacket *packet = talz(ctx, struct onionpacket);
 	int i, num_hops = tal_count(path);
-	u8 filler[2 * (num_hops - 1) * SECURITY_PARAMETER];
+	u8 filler[(num_hops - 1) * HOP_DATA_SIZE];
 	struct keyset keys;
 	u8 nextaddr[20], nexthmac[SECURITY_PARAMETER];
 	u8 stream[ROUTING_INFO_SIZE];
@@ -353,22 +379,22 @@ struct onionpacket *create_onionpacket(
 	memset(nexthmac, 0, 20);
 	memset(packet->routinginfo, 0, ROUTING_INFO_SIZE);
 
-	generate_header_padding(filler, sizeof(filler), 2 * SECURITY_PARAMETER,
+	generate_header_padding(filler, sizeof(filler), HOP_DATA_SIZE,
 				"rho", 3, num_hops, params);
 
 	for (i = num_hops - 1; i >= 0; i--) {
+		memcpy(hops_data[i].hmac, nexthmac, SECURITY_PARAMETER);
 		generate_key_set(params[i].secret, &keys);
 		generate_cipher_stream(stream, keys.rho, ROUTING_INFO_SIZE);
 
 		/* Rightshift mix-header by 2*SECURITY_PARAMETER */
-		memmove(packet->routinginfo + 2 * SECURITY_PARAMETER, packet->routinginfo,
-			ROUTING_INFO_SIZE - 2 * SECURITY_PARAMETER);
-		memcpy(packet->routinginfo, nextaddr, SECURITY_PARAMETER);
-		memcpy(packet->routinginfo + SECURITY_PARAMETER, nexthmac, SECURITY_PARAMETER);
+		memmove(packet->routinginfo + HOP_DATA_SIZE, packet->routinginfo,
+			ROUTING_INFO_SIZE - HOP_DATA_SIZE);
+		serialize_hop_data(packet, packet->routinginfo, &hops_data[i]);
 		xorbytes(packet->routinginfo, packet->routinginfo, stream, ROUTING_INFO_SIZE);
 
 		if (i == num_hops - 1) {
-			size_t len = (NUM_MAX_HOPS - num_hops + 1) * 2 * SECURITY_PARAMETER;
+			size_t len = (NUM_MAX_HOPS - num_hops + 1) * HOP_DATA_SIZE;
 			memcpy(packet->routinginfo + len, filler, sizeof(filler));
 		}
 
@@ -398,7 +424,7 @@ struct route_step *process_onionpacket(
 	struct keyset keys;
 	u8 blind[BLINDING_FACTOR_SIZE];
 	u8 stream[NUM_STREAM_BYTES];
-	u8 paddedheader[ROUTING_INFO_SIZE + 2 * SECURITY_PARAMETER];
+	u8 paddedheader[ROUTING_INFO_SIZE + HOP_DATA_SIZE];
 
 	step->next = talz(step, struct onionpacket);
 	step->next->version = msg->version;
@@ -421,12 +447,12 @@ struct route_step *process_onionpacket(
 	compute_blinding_factor(&msg->ephemeralkey, shared_secret, blind);
 	if (!blind_group_element(&step->next->ephemeralkey, &msg->ephemeralkey, blind))
 		return tal_free(step);
-	memcpy(&step->next->nexthop, paddedheader, SECURITY_PARAMETER);
-	memcpy(&step->next->mac,
-	       paddedheader + SECURITY_PARAMETER,
-	       SECURITY_PARAMETER);
 
-	memcpy(&step->next->routinginfo, paddedheader + 2 * SECURITY_PARAMETER, ROUTING_INFO_SIZE);
+	deserialize_hop_data(&step->hop_data, paddedheader);
+
+        memcpy(&step->next->mac, step->hop_data.hmac, SECURITY_PARAMETER);
+
+	memcpy(&step->next->routinginfo, paddedheader + HOP_DATA_SIZE, ROUTING_INFO_SIZE);
 
 	if (memeqzero(step->next->mac, sizeof(step->next->mac))) {
 		step->nextcase = ONION_END;

lightningd/sphinx.h

@@ -9,11 +9,12 @@
 #include <ccan/tal/tal.h>
 #include <secp256k1.h>
 #include <sodium/randombytes.h>
+#include <wire/wire.h>
 
 #define SECURITY_PARAMETER 20
 #define NUM_MAX_HOPS 20
-#define HOP_DATA_SIZE 40
-#define ROUTING_INFO_SIZE (HOP_DATA_SIZE * SECURITY_PARAMETER)
+#define HOP_DATA_SIZE 53
+#define ROUTING_INFO_SIZE (HOP_DATA_SIZE * NUM_MAX_HOPS)
 #define TOTAL_PACKET_SIZE (1 + 33 + SECURITY_PARAMETER + ROUTING_INFO_SIZE)
 
 struct onionpacket {
@@ -34,23 +35,35 @@ enum route_next_case {
 
 /* BOLT #4:
  *
- * The format of the per-hop-payload for a version 0 packet is as follows:
+ * The hops_data field is a structure that holds obfuscated versions of the next hop's address, transfer information and the associated HMAC. It is 1060 bytes long, and has the following structure:
+
+```
++-----------+-------------+----------+-----------+-------------+----------+-----------+
+| n_1 realm | n_1 per-hop | n_1 HMAC | n_2 realm | n_2 per-hop | n_2 HMAC | ...filler |
++-----------+-------------+----------+----------+--------------+----------+------------+
+```
+
+The realm byte determines the format of the per-hop; so far only realm 0 is defined, and for that, the per-hop format is:
+
 ```
-+----------------+--------------------------+-------------------------------+--------------------------------------------+
-| realm (1 byte) | amt_to_forward (8 bytes) | outgoing_cltv_value (4 bytes) | unused_with_v0_version_on_header (7 bytes) |
-+----------------+--------------------------+-------------------------------+--------------------------------------------+
++----------------------+--------------------------+-------------------------------+--------------------+
+| channel_id (8 bytes) | amt_to_forward (4 bytes) | outgoing_cltv_value (4 bytes) | padding (16 bytes) |
++----------------------+--------------------------+-------------------------------+--------------------+
 ```
 */
-struct hoppayload {
+struct hop_data {
 	u8 realm;
-	u64 amt_to_forward;
-	u32 outgoing_cltv_value;
-	u8 unused_with_v0_version_on_header[7];
+	struct short_channel_id channel_id;
+	u32 amt_forward;
+	u32 outgoing_cltv;
+	/* Padding omitted, will be zeroed */
+	u8 hmac[SECURITY_PARAMETER];
 };
 
 struct route_step {
 	enum route_next_case nextcase;
 	struct onionpacket *next;
+	struct hop_data hop_data;
 };
 
 /**
@@ -69,6 +82,7 @@ struct route_step {
 struct onionpacket *create_onionpacket(
 	const tal_t * ctx,
 	struct pubkey path[],
+	struct hop_data hops_data[],
 	const u8 * sessionkey,
 	const u8 *assocdata,
 	const size_t assocdatalen

test/test_sphinx.c

@@ -131,6 +131,7 @@ int main(int argc, char **argv)
 		struct pubkey *path = tal_arr(ctx, struct pubkey, num_hops);
 		u8 privkeys[argc - 1][32];
 		u8 sessionkey[32];
+		struct hop_data hops_data[num_hops];
 
 		memset(&sessionkey, 'A', sizeof(sessionkey));
 
@@ -141,9 +142,13 @@ int main(int argc, char **argv)
 				return 1;
 		}
 
+		for (i=0; i<num_hops; i++) {
+			memset(&hops_data[i], 'A', sizeof(hops_data[i]));
+		}
 
 		struct onionpacket *res = create_onionpacket(ctx,
 							     path,
+							     hops_data,
 							     sessionkey,
 							     assocdata,
 							     sizeof(assocdata));