sphinx: Parameterizing the HMAC size

Should have done this a long time ago...

lightningd/sphinx.c

@@ -1,4 +1,4 @@
-#include "sphinx.h"
+#include "lightningd/sphinx.h"
 #include "utils.h"
 #include <assert.h>
 
@@ -101,7 +101,7 @@ struct onionpacket *parse_onionpacket(
 		return tal_free(m);
 
 	read_buffer(&m->routinginfo, src, ROUTING_INFO_SIZE, &p);
-	read_buffer(&m->mac, src, 20, &p);
+	read_buffer(&m->mac, src, SECURITY_PARAMETER, &p);
 	return m;
 }
 
@@ -151,7 +151,7 @@ static void compute_packet_hmac(const struct onionpacket *packet,
 	write_buffer(mactemp, assocdata, assocdatalen, &pos);
 
 	compute_hmac(mac, mactemp, sizeof(mactemp), mukey, KEY_LEN);
-	memcpy(hmac, mac, 20);
+	memcpy(hmac, mac, SECURITY_PARAMETER);
 }
 
 static bool generate_key(void *k, const char *t, u8 tlen, const u8 *s)
@@ -375,7 +375,7 @@ struct onionpacket *create_onionpacket(
 	if (!params)
 		return NULL;
 	packet->version = 1;
-	memset(nexthmac, 0, 20);
+	memset(nexthmac, 0, SECURITY_PARAMETER);
 	memset(packet->routinginfo, 0, ROUTING_INFO_SIZE);
 
 	generate_header_padding(filler, sizeof(filler), HOP_DATA_SIZE,
@@ -418,7 +418,7 @@ struct route_step *process_onionpacket(
 	)
 {
 	struct route_step *step = talz(ctx, struct route_step);
-	u8 hmac[20];
+	u8 hmac[SECURITY_PARAMETER];
 	struct keyset keys;
 	u8 blind[BLINDING_FACTOR_SIZE];
 	u8 stream[NUM_STREAM_BYTES];

lightningd/sphinx.h

@@ -11,16 +11,17 @@
 #include <sodium/randombytes.h>
 #include <wire/wire.h>
 
-#define SECURITY_PARAMETER 20
+#define SECURITY_PARAMETER 32
 #define NUM_MAX_HOPS 20
-#define HOP_DATA_SIZE 53
+#define PAYLOAD_SIZE 32
+#define HOP_DATA_SIZE (1 + SECURITY_PARAMETER + PAYLOAD_SIZE)
 #define ROUTING_INFO_SIZE (HOP_DATA_SIZE * NUM_MAX_HOPS)
 #define TOTAL_PACKET_SIZE (1 + 33 + SECURITY_PARAMETER + ROUTING_INFO_SIZE)
 
 struct onionpacket {
 	/* Cleartext information */
 	u8 version;
-	u8 mac[20];
+	u8 mac[SECURITY_PARAMETER];
 	secp256k1_pubkey ephemeralkey;
 
 	/* Encrypted information */
@@ -74,7 +75,7 @@ struct route_step {
  * @hoppayloads: payloads destined for individual hosts (limited to
  *    HOP_PAYLOAD_SIZE bytes)
  * @num_hops: path length in nodes
- * @sessionkey: 20 byte random session key to derive secrets from
+ * @sessionkey: 32 byte random session key to derive secrets from
  * @assocdata: associated data to commit to in HMACs
  * @assocdatalen: length of the assocdata
  */