sphinx: Add function to add a new v0 hop to a sphinx_path

This is just taking the existing serialization code and repackaging it in a
more useful form.

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

common/sphinx.c

@@ -4,6 +4,7 @@
 #include <ccan/crypto/ripemd160/ripemd160.h>
 #include <ccan/crypto/sha256/sha256.h>
 #include <ccan/mem/mem.h>
+#include <common/node_id.h>
 #include <common/sphinx.h>
 #include <common/utils.h>
 
@@ -85,6 +86,67 @@ struct sphinx_path *sphinx_path_new_with_key(const tal_t *ctx,
 	return sp;
 }
 
+static size_t sphinx_hop_size(const struct sphinx_hop *hop)
+{
+	size_t size = tal_bytelen(hop->payload), vsize;
+
+	/* There is no point really in trying to serialize something that is
+	 * larger than the maximum length we can fit into the payload region
+	 * anyway. 3 here is the maximum varint size that we allow. */
+	assert(size < ROUTING_INFO_SIZE - 3 - HMAC_SIZE);
+
+	/* Backwards compatibility: realm 0 is the legacy hop_data format and
+	 * always has 65 bytes in size */
+	if (hop->realm == 0x00)
+		return 65;
+
+	/* Since this uses the bigsize serialization format for variable
+	 * length integer encodings we need to allocate enough space for
+	 * it. Values >= 0xfd are used to signal multi-byte serializations. */
+	if (size < 0xFD)
+		vsize = 1;
+	else
+		vsize = 3;
+
+	/* The hop must accomodate the hop_payload, as well as the varint
+	 * describing the length and HMAC. */
+	return vsize + size + HMAC_SIZE;
+}
+
+static size_t sphinx_path_payloads_size(const struct sphinx_path *path)
+{
+	size_t size = 0;
+	for (size_t i=0; i<tal_count(path->hops); i++)
+		size += sphinx_hop_size(&path->hops[i]);
+	return size;
+}
+
+/**
+ * Add a raw payload hop to the path.
+ */
+static void sphinx_add_raw_hop(struct sphinx_path *path,
+			       const struct pubkey *pubkey, u8 realm,
+			       const u8 *payload)
+{
+	struct sphinx_hop sp;
+	sp.payload = payload;
+	sp.realm = realm;
+	sp.pubkey = *pubkey;
+	tal_arr_expand(&path->hops, sp);
+	assert(sphinx_path_payloads_size(path) <= ROUTING_INFO_SIZE);
+}
+
+void sphinx_add_v0_hop(struct sphinx_path *path, const struct pubkey *pubkey,
+		       const struct short_channel_id *scid,
+		       struct amount_msat forward, u32 outgoing_cltv)
+{
+	u8 *buf = tal_arr(path, u8, 0);
+	towire_short_channel_id(&buf, scid);
+	towire_u64(&buf, forward.millisatoshis); /* Raw: low-level serializer */
+	towire_u32(&buf, outgoing_cltv);
+	sphinx_add_raw_hop(path, pubkey, 0, buf);
+}
+
 /* Small helper to append data to a buffer and update the position
  * into the buffer
  */
@@ -247,28 +309,24 @@ static void compute_blinding_factor(const struct pubkey *key,
 	memcpy(res, &temp, 32);
 }
 
-static bool blind_group_element(
-	struct pubkey *blindedelement,
+static bool blind_group_element(struct pubkey *blindedelement,
 				const struct pubkey *pubkey,
 				const u8 blind[BLINDING_FACTOR_SIZE])
 {
 	/* tweak_mul is inplace so copy first. */
 	if (pubkey != blindedelement)
 		*blindedelement = *pubkey;
-	if (secp256k1_ec_pubkey_tweak_mul(secp256k1_ctx, &blindedelement->pubkey, blind) != 1)
+	if (secp256k1_ec_pubkey_tweak_mul(secp256k1_ctx,
+					  &blindedelement->pubkey, blind) != 1)
 		return false;
 	return true;
 }
 
-static bool create_shared_secret(
-	u8 *secret,
-	const struct pubkey *pubkey,
-	const u8 *sessionkey)
+static bool create_shared_secret(u8 *secret, const struct pubkey *pubkey,
+				 const struct secret *session_key)
 {
-
-	if (secp256k1_ecdh(secp256k1_ctx, secret, &pubkey->pubkey, sessionkey,
-			   NULL, NULL)
-	    != 1)
+	if (secp256k1_ecdh(secp256k1_ctx, secret, &pubkey->pubkey,
+			   session_key->data, NULL, NULL) != 1)
 		return false;
 	return true;
 }
@@ -279,7 +337,7 @@ bool onion_shared_secret(
 	const struct privkey *privkey)
 {
 	return create_shared_secret(secret, &packet->ephemeralkey,
-				    privkey->secret.data);
+				    &privkey->secret);
 }
 
 static void generate_key_set(const u8 secret[SHARED_SECRET_SIZE],
@@ -294,19 +352,21 @@ static void generate_key_set(const u8 secret[SHARED_SECRET_SIZE],
 static struct hop_params *generate_hop_params(
 	const tal_t *ctx,
 	const u8 *sessionkey,
-	struct pubkey path[])
+	struct sphinx_path *path)
 {
-	int i, j, num_hops = tal_count(path);
+	int i, j, num_hops = tal_count(path->hops);
 	struct pubkey temp;
 	u8 blind[BLINDING_FACTOR_SIZE];
 	struct hop_params *params = tal_arr(ctx, struct hop_params, num_hops);
 
 	/* Initialize the first hop with the raw information */
-	if (secp256k1_ec_pubkey_create(
-		    secp256k1_ctx, &params[0].ephemeralkey.pubkey, sessionkey) != 1)
+	if (secp256k1_ec_pubkey_create(secp256k1_ctx,
+				       &params[0].ephemeralkey.pubkey,
+				       path->session_key->data) != 1)
 		return NULL;
 
-	if (!create_shared_secret(params[0].secret, &path[0], sessionkey))
+	if (!create_shared_secret(params[0].secret, &path->hops[0].pubkey,
+				  path->session_key))
 		return NULL;
 
 	compute_blinding_factor(
@@ -327,7 +387,7 @@ static struct hop_params *generate_hop_params(
 		 * Order is indifferent, multiplication is commutative.
 		 */
 		memcpy(&blind, sessionkey, 32);
-		temp = path[i];
+		temp = path->hops[i].pubkey;
 		if (!blind_group_element(&temp, &temp, blind))
 			return NULL;
 		for (j = 0; j < i; j++)
@@ -353,19 +413,6 @@ 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_amount_msat(&buf, data->amt_forward);
-	towire_u32(&buf, data->outgoing_cltv);
-	towire_pad(&buf, 12);
-	towire(&buf, data->hmac, HMAC_SIZE);
-	memcpy(dst, buf, tal_count(buf));
-	tal_free(buf);
-}
-
 static void deserialize_hop_data(struct hop_data *data, const u8 *src)
 {
 	const u8 *cursor = src;
@@ -378,25 +425,35 @@ static void deserialize_hop_data(struct hop_data *data, const u8 *src)
 	fromwire(&cursor, &max, &data->hmac, HMAC_SIZE);
 }
 
+static void sphinx_write_frame(u8 *dest, const struct sphinx_hop *hop)
+{
+		memset(dest, 0, FRAME_SIZE);
+		dest[0] = hop->realm;
+		memcpy(dest + 1, hop->payload, tal_bytelen(hop->payload));
+		memcpy(dest + FRAME_SIZE - HMAC_SIZE, hop->hmac, HMAC_SIZE);
+}
+
 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,
+	struct sphinx_path *sp,
 	struct secret **path_secrets
 	)
 {
 	struct onionpacket *packet = talz(ctx, struct onionpacket);
-	int i, num_hops = tal_count(path);
+	int i, num_hops = tal_count(sp->hops);
 	u8 filler[(num_hops - 1) * FRAME_SIZE];
 	struct keyset keys;
 	u8 nexthmac[HMAC_SIZE];
 	u8 stream[ROUTING_INFO_SIZE];
-	struct hop_params *params = generate_hop_params(ctx, sessionkey, path);
+	struct hop_params *params;
 	struct secret *secrets = tal_arr(ctx, struct secret, num_hops);
 
+	if (sp->session_key == NULL) {
+		sp->session_key = tal(sp, struct secret);
+		randombytes_buf(sp->session_key, sizeof(struct secret));
+	}
+
+	params = generate_hop_params(ctx, sp->session_key->data, sp);
 	if (!params) {
 		tal_free(packet);
 		tal_free(secrets);
@@ -410,15 +467,15 @@ struct onionpacket *create_onionpacket(
 				"rho", 3, num_hops, params);
 
 	for (i = num_hops - 1; i >= 0; i--) {
-		memcpy(hops_data[i].hmac, nexthmac, HMAC_SIZE);
-		hops_data[i].realm = 0;
+		memcpy(sp->hops[i].hmac, nexthmac, HMAC_SIZE);
 		generate_key_set(params[i].secret, &keys);
 		generate_cipher_stream(stream, keys.rho, ROUTING_INFO_SIZE);
 
-		/* Rightshift mix-header by 2*HMAC_SIZE */
+		/* Rightshift mix-header by FRAME_SIZE */
 		memmove(packet->routinginfo + FRAME_SIZE, packet->routinginfo,
 			ROUTING_INFO_SIZE - FRAME_SIZE);
-		serialize_hop_data(packet, packet->routinginfo, &hops_data[i]);
+		sphinx_write_frame(packet->routinginfo, &sp->hops[i]);
+
 		xorbytes(packet->routinginfo, packet->routinginfo, stream, ROUTING_INFO_SIZE);
 
 		if (i == num_hops - 1) {
@@ -426,7 +483,7 @@ struct onionpacket *create_onionpacket(
 			memcpy(packet->routinginfo + len, filler, sizeof(filler));
 		}
 
-		compute_packet_hmac(packet, assocdata, assocdatalen, keys.mu,
+		compute_packet_hmac(packet, sp->associated_data, tal_bytelen(sp->associated_data), keys.mu,
 				    nexthmac);
 	}
 	memcpy(packet->mac, nexthmac, sizeof(nexthmac));

common/sphinx.h

@@ -110,11 +110,7 @@ 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,
+	struct sphinx_path *sp,
 	struct secret **path_secrets
 	);
 
@@ -231,4 +227,10 @@ struct sphinx_path *sphinx_path_new_with_key(const tal_t *ctx,
 					     const u8 *associated_data,
 					     const struct secret *session_key);
 
+/**
+ * Add a V0 (Realm 0) single frame hop to the path.
+ */
+void sphinx_add_v0_hop(struct sphinx_path *path, const struct pubkey *pubkey,
+		       const struct short_channel_id *scid,
+		       struct amount_msat forward, u32 outgoing_cltv);
 #endif /* LIGHTNING_COMMON_SPHINX_H */

common/test/run-sphinx.c

@@ -56,6 +56,9 @@ void towire_u16(u8 **pptr UNNEEDED, u16 v UNNEEDED)
 /* Generated stub for towire_u32 */
 void towire_u32(u8 **pptr UNNEEDED, u32 v UNNEEDED)
 { fprintf(stderr, "towire_u32 called!\n"); abort(); }
+/* Generated stub for towire_u64 */
+void towire_u64(u8 **pptr UNNEEDED, u64 v UNNEEDED)
+{ fprintf(stderr, "towire_u64 called!\n"); abort(); }
 /* Generated stub for towire_u8 */
 void towire_u8(u8 **pptr UNNEEDED, u8 v UNNEEDED)
 { fprintf(stderr, "towire_u8 called!\n"); abort(); }

devtools/onion.c

@@ -3,6 +3,7 @@
 #include <ccan/read_write_all/read_write_all.h>
 #include <ccan/short_types/short_types.h>
 #include <ccan/str/hex/hex.h>
+#include <common/amount.h>
 #include <common/sphinx.h>
 #include <common/utils.h>
 #include <err.h>
@@ -19,11 +20,15 @@ static void do_generate(int argc, char **argv,
 	int num_hops = argc - 1;
 	struct pubkey *path = tal_arr(ctx, struct pubkey, num_hops);
 	u8 privkeys[argc - 1][32];
-	u8 sessionkey[32];
+	struct secret session_key;
 	struct hop_data hops_data[num_hops];
 	struct secret *shared_secrets;
+	struct sphinx_path *sp;
 
-	memset(&sessionkey, 'A', sizeof(sessionkey));
+	assocdata = tal_arr(ctx, u8, 32);
+	memset(&session_key, 'A', sizeof(struct secret));
+
+	sp = sphinx_path_new_with_key(ctx, assocdata, &session_key);
 
 	for (int i = 0; i < num_hops; i++) {
 		size_t klen = strcspn(argv[1 + i], "/");
@@ -33,8 +38,9 @@ static void do_generate(int argc, char **argv,
 		if (secp256k1_ec_pubkey_create(secp256k1_ctx, &path[i].pubkey,
 					       privkeys[i]) != 1)
 			errx(1, "Could not decode pubkey");
-		printf("# Node %d pubkey %s\n",
-		       i, secp256k1_pubkey_to_hexstr(ctx, &path[i].pubkey));
+		fprintf(stderr, "Node %d pubkey %s\n", i,
+			secp256k1_pubkey_to_hexstr(ctx, &path[i].pubkey));
+
 		memset(&hops_data[i], 0, sizeof(hops_data[i]));
 		if (argv[1 + i][klen] != '\0') {
 			/* FIXME: Generic realm support, not this hack! */
@@ -76,11 +82,12 @@ static void do_generate(int argc, char **argv,
 			hops_data[i].amt_forward.millisatoshis = i; /* Raw: test code */
 			hops_data[i].outgoing_cltv = i;
 		}
+		fprintf(stderr, "Hopdata %d: %s\n", i, tal_hexstr(NULL, &hops_data[i], sizeof(hops_data[i])));
+		sphinx_add_v0_hop(sp, &path[i], &hops_data[i].channel_id, hops_data[i].amt_forward, i);
 	}
 
 	struct onionpacket *res =
-	    create_onionpacket(ctx, path, hops_data, sessionkey,
-			       assocdata, ASSOC_DATA_SIZE, &shared_secrets);
+		create_onionpacket(ctx, sp, &shared_secrets);
 
 	u8 *serialized = serialize_onionpacket(ctx, res);
 	if (!serialized)

lightningd/pay.c

@@ -590,37 +590,36 @@ send_payment(struct lightningd *ld,
 	enum onion_type failcode;
 	size_t i, n_hops = tal_count(route);
 	struct hop_data *hop_data = tal_arr(tmpctx, struct hop_data, n_hops);
-	struct pubkey *path = tal_arr(tmpctx, struct pubkey, n_hops);
 	struct node_id *ids = tal_arr(tmpctx, struct node_id, n_hops);
 	struct wallet_payment *payment = NULL;
 	struct htlc_out *hout;
 	struct short_channel_id *channels;
 	struct routing_failure *fail;
 	struct channel *channel;
+	struct sphinx_path *path;
+	struct short_channel_id finalscid;
+	struct pubkey pubkey;
+	bool ret;
 
 	/* Expiry for HTLCs is absolute.  And add one to give some margin. */
 	base_expiry = get_block_height(ld->topology) + 1;
 
-	/* Extract IDs for each hop: create_onionpacket wants array of *keys*,
-	 * and wallet wants continuous array of node_ids */
-	for (i = 0; i < n_hops; i++) {
+	path = sphinx_path_new(tmpctx, rhash->u.u8);
+	/* Extract IDs for each hop: create_onionpacket wants array. */
+	for (i = 0; i < n_hops; i++)
 		ids[i] = route[i].nodeid;
-		/* JSON parsing checked these were valid, so Shouldn't Happen */
-		if (!pubkey_from_node_id(&path[i], &ids[i])) {
-			return command_fail(cmd, PAY_UNSPECIFIED_ERROR,
-					    "Invalid nodeid %s",
-					    type_to_string(tmpctx,
-							   struct node_id,
-							   &ids[i]));
-		}
-	}
 
 	/* Copy hop_data[n] from route[n+1] (ie. where it goes next) */
 	for (i = 0; i < n_hops - 1; i++) {
+		ret = pubkey_from_node_id(&pubkey, &ids[i]);
+		assert(ret);
 		hop_data[i].realm = 0;
 		hop_data[i].channel_id = route[i+1].channel_id;
 		hop_data[i].amt_forward = route[i+1].amount;
 		hop_data[i].outgoing_cltv = base_expiry + route[i+1].delay;
+		sphinx_add_v0_hop(path, &pubkey, &route[i + 1].channel_id,
+				  route[i + 1].amount,
+				  base_expiry + route[i + 1].delay);
 	}
 
 	/* And finally set the final hop to the special values in
@@ -630,6 +629,13 @@ send_payment(struct lightningd *ld,
 	memset(&hop_data[i].channel_id, 0, sizeof(struct short_channel_id));
 	hop_data[i].amt_forward = route[i].amount;
 
+	memset(&finalscid, 0, sizeof(struct short_channel_id));
+	ret = pubkey_from_node_id(&pubkey, &ids[i]);
+	assert(ret);
+	sphinx_add_v0_hop(path, &pubkey, &finalscid,
+			  route[i].amount,
+			  base_expiry + route[i].delay);
+
 	/* Now, do we already have a payment? */
 	payment = wallet_payment_by_hash(tmpctx, ld->wallet, rhash);
 	if (payment) {
@@ -679,8 +685,7 @@ send_payment(struct lightningd *ld,
 	randombytes_buf(&sessionkey, sizeof(sessionkey));
 
 	/* Onion will carry us from first peer onwards. */
-	packet = create_onionpacket(tmpctx, path, hop_data, sessionkey, rhash->u.u8,
-				    sizeof(struct sha256), &path_secrets);
+	packet = create_onionpacket(tmpctx, path, &path_secrets);
 	onion = serialize_onionpacket(tmpctx, packet);
 
 	log_info(ld->log, "Sending %s over %zu hops to deliver %s",