developer: add --dev-force-privkey to allow setting a specific node key.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

hsmd/hsm_wire.csv

@@ -9,6 +9,7 @@ hsmstatus_client_bad_request,,msg,len*u8
 # Start the HSM.
 hsm_init,11
 hsm_init,,bip32_key_version,struct bip32_key_version
+hsm_init,,dev_force_privkey,?struct privkey
 
 #include <common/bip32.h>
 hsm_init_reply,111

hsmd/hsmd.c

@@ -72,6 +72,11 @@ static struct {
  * so set it static.*/
 static struct  bip32_key_version  bip32_key_version;
 
+#if DEVELOPER
+/* If they specify --dev-force-privkey it ends up in here. */
+static struct privkey *dev_force_privkey;
+#endif
+
 /*~ We keep track of clients, but there's not much to keep. */
 struct client {
 	/* The ccan/io async io connection for this client: it closes, we die. */
@@ -314,6 +319,17 @@ static void node_key(struct privkey *node_privkey, struct pubkey *node_id)
 		salt++;
 	} while (!secp256k1_ec_pubkey_create(secp256k1_ctx, &node_id->pubkey,
 					     node_privkey->secret.data));
+
+#if DEVELOPER
+	/* In DEVELOPER mode, we can override with --dev-force-privkey */
+	if (dev_force_privkey) {
+		*node_privkey = *dev_force_privkey;
+		if (!secp256k1_ec_pubkey_create(secp256k1_ctx, &node_id->pubkey,
+						node_privkey->secret.data))
+			status_failed(STATUS_FAIL_INTERNAL_ERROR,
+				      "Failed to derive pubkey for dev_force_privkey");
+	}
+#endif
 }
 
 /*~ This secret is the basis for all per-channel secrets: the per-channel seeds
@@ -540,6 +556,7 @@ static struct io_plan *init_hsm(struct io_conn *conn,
 {
 	struct node_id node_id;
 	struct pubkey key;
+	struct privkey *privkey;
 
 	/* This must be lightningd. */
 	assert(is_lightningd(c));
@@ -548,9 +565,12 @@ static struct io_plan *init_hsm(struct io_conn *conn,
 	 * definitions in hsm_client_wire.csv.  The format of those files is
 	 * an extension of the simple comma-separated format output by the
 	 * BOLT tools/extract-formats.py tool. */
-	if (!fromwire_hsm_init(msg_in, &bip32_key_version))
+	if (!fromwire_hsm_init(NULL, msg_in, &bip32_key_version, &privkey))
 		return bad_req(conn, c, msg_in);
 
+#if DEVELOPER
+	dev_force_privkey = privkey;
+#endif
 	maybe_create_new_hsm();
 	load_hsm();
 
@@ -1601,6 +1621,8 @@ static struct io_plan *handle_memleak(struct io_conn *conn,
 	memleak_remove_uintmap(memtable, &clients);
 	memleak_scan_region(memtable, status_conn, tal_bytelen(status_conn));
 
+	memleak_scan_region(memtable, dev_force_privkey, 0);
+
 	found_leak = dump_memleak(memtable);
 	reply = towire_hsm_dev_memleak_reply(NULL, found_leak);
 	return req_reply(conn, c, take(reply));

lightningd/hsm_control.c

@@ -94,7 +94,13 @@ void hsm_init(struct lightningd *ld)
 
 	ld->hsm_fd = fds[0];
 	if (!wire_sync_write(ld->hsm_fd, towire_hsm_init(tmpctx,
-				  &ld->topology->bitcoind->chainparams->bip32_key_version)))
+				  &ld->topology->bitcoind->chainparams->bip32_key_version,
+#if DEVELOPER
+							 ld->dev_force_privkey
+#else
+							 NULL
+#endif
+				     )))
 		err(1, "Writing init msg to hsm");
 
 	ld->wallet->bip32_base = tal(ld->wallet, struct ext_key);

lightningd/lightningd.c

@@ -118,6 +118,7 @@ static struct lightningd *new_lightningd(const tal_t *ctx)
 	ld->dev_subdaemon_fail = false;
 	ld->dev_allow_localhost = false;
 	ld->dev_gossip_time = 0;
+	ld->dev_force_privkey = NULL;
 #endif
 
 	/*~ These are CCAN lists: an embedded double-linked list.  It's not

lightningd/lightningd.h

@@ -205,6 +205,9 @@ struct lightningd {
 
 	/* Things we've marked as not leaking. */
 	const void **notleaks;
+
+	/* This is the forced private key for the node. */
+	struct privkey *dev_force_privkey;
 #endif /* DEVELOPER */
 
 	/* tor support */

lightningd/options.c

@@ -7,6 +7,7 @@
 #include <ccan/opt/private.h>
 #include <ccan/read_write_all/read_write_all.h>
 #include <ccan/short_types/short_types.h>
+#include <ccan/str/hex/hex.h>
 #include <ccan/tal/grab_file/grab_file.h>
 #include <ccan/tal/path/path.h>
 #include <ccan/tal/str/str.h>
@@ -438,6 +439,16 @@ static char *opt_subprocess_debug(const char *optarg, struct lightningd *ld)
 	return NULL;
 }
 
+static char *opt_force_privkey(const char *optarg, struct lightningd *ld)
+{
+	tal_free(ld->dev_force_privkey);
+	ld->dev_force_privkey = tal(ld, struct privkey);
+	if (!hex_decode(optarg, strlen(optarg),
+			ld->dev_force_privkey, sizeof(*ld->dev_force_privkey)))
+		return tal_fmt(NULL, "Unable to parse privkey '%s'", optarg);
+	return NULL;
+}
+
 static void dev_register_opts(struct lightningd *ld)
 {
 	opt_register_noarg("--dev-no-reconnect", opt_set_invbool,
@@ -474,6 +485,8 @@ static void dev_register_opts(struct lightningd *ld)
 	opt_register_arg("--dev-gossip-time", opt_set_u32, opt_show_u32,
 			 &ld->dev_gossip_time,
 			 "UNIX time to override gossipd to use.");
+	opt_register_arg("--dev-force-privkey", opt_force_privkey, NULL, ld,
+			 "Force HSM to use this as node private key");
  }
 #endif