hsmtool: makerune command.

You still need to actually make a rune when lightningd starts, as
commando (for safety) won't work unless you actually generate a rune
(that it knows of!).

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Changelog-Added: hsmtool: `makerune` command to make a master rune for a node.

doc/lightning-hsmtool.8.md

@@ -68,6 +68,11 @@ We need the path to the hsm\_secret containing the wallet seed, and an optional
 To generate descriptors using testnet master keys, you may specify *testnet* as
 the last parameter. By default, mainnet-encoded keys are generated.
 
+**makerune** *hsm\_secret*
+  Make a master rune for this node (with `uniqueid` 0)
+This produces the same results as lightning-commando-rune(7) on a fresh node.
+You will still need to create a rune once the node starts, if you want commando to work (as it is only activated once it has generated one).
+
 BUGS
 ----
 

tests/test_wallet.py

@@ -1667,3 +1667,34 @@ def test_upgradewallet(node_factory, bitcoind):
     sync_blockheight(l1.bitcoin, [l1])
     upgrade = l1.rpc.upgradewallet(feerate="urgent", reservedok=True)
     assert upgrade['upgraded_outs'] == 0
+
+
+def test_hsmtool_makerune(node_factory):
+    """Test we can make a valid rune before the node really exists"""
+    l1 = node_factory.get_node(start=False)
+
+    # get_node() creates a secret, but in usual case we generate one.
+    hsm_path = os.path.join(l1.daemon.lightning_dir, TEST_NETWORK, "hsm_secret")
+    os.remove(hsm_path)
+
+    hsmtool = HsmTool(node_factory.directory, "generatehsm", hsm_path)
+    master_fd, slave_fd = os.openpty()
+    hsmtool.start(stdin=slave_fd)
+    hsmtool.wait_for_log(r"Select your language:")
+    write_all(master_fd, "0\n".encode("utf-8"))
+    hsmtool.wait_for_log(r"Introduce your BIP39 word list")
+    write_all(master_fd, "ritual idle hat sunny universe pluck key alpha wing "
+              "cake have wedding\n".encode("utf-8"))
+    hsmtool.wait_for_log(r"Enter your passphrase:")
+    write_all(master_fd, "This is actually not a passphrase\n".encode("utf-8"))
+    assert hsmtool.proc.wait(WAIT_TIMEOUT) == 0
+    hsmtool.is_in_log(r"New hsm_secret file created")
+
+    cmd_line = ["tools/hsmtool", "makerune", hsm_path]
+    out = subprocess.check_output(cmd_line).decode("utf8").split("\n")[0]
+
+    l1.start()
+
+    # We have to generate a rune now, for commando to even start processing!
+    rune = l1.rpc.commando_rune()['rune']
+    assert rune == out

tools/hsmtool.c

@@ -4,6 +4,7 @@
 #include <ccan/err/err.h>
 #include <ccan/noerr/noerr.h>
 #include <ccan/read_write_all/read_write_all.h>
+#include <ccan/rune/rune.h>
 #include <ccan/tal/grab_file/grab_file.h>
 #include <ccan/tal/path/path.h>
 #include <ccan/tal/str/str.h>
@@ -42,6 +43,7 @@ static void show_usage(const char *progname)
 	printf("	- generatehsm <path/to/new/hsm_secret>\n");
 	printf("	- checkhsm <path/to/new/hsm_secret>\n");
 	printf("	- dumponchaindescriptors <path/to/hsm_secret> [network]\n");
+	printf("	- makerune <path/to/hsm_secret>\n");
 	exit(0);
 }
 
@@ -611,6 +613,33 @@ static int check_hsm(const char *hsm_secret_path)
 	return 0;
 }
 
+static int make_rune(const char *hsm_secret_path)
+{
+	struct secret hsm_secret, derived_secret, rune_secret;
+	struct rune *master_rune, *rune;
+
+	/* Get hsm_secret */
+	get_hsm_secret(&hsm_secret, hsm_secret_path);
+
+	/* HSM derives a root secret for `makesecret` */
+	hkdf_sha256(&derived_secret, sizeof(struct secret), NULL, 0,
+		    &hsm_secret, sizeof(hsm_secret),
+		    "derived secrets", strlen("derived secrets"));
+
+	/* Commando derives secret using makesecret "commando" */
+	hkdf_sha256(&rune_secret, sizeof(struct secret), NULL, 0,
+		    &derived_secret, sizeof(derived_secret),
+		    "commando", strlen("commando"));
+
+	master_rune = rune_new(tmpctx,
+			       rune_secret.data,
+			       ARRAY_SIZE(rune_secret.data),
+			       NULL);
+	rune = rune_derive_start(tmpctx, master_rune, "0");
+	printf("%s\n", rune_to_base64(tmpctx, rune));
+	return 0;
+}
+
 int main(int argc, char *argv[])
 {
 	const char *method;
@@ -703,5 +732,11 @@ int main(int argc, char *argv[])
 		return check_hsm(argv[2]);
 	}
 
+	if (streq(method, "makerune")) {
+		if (argc < 3)
+			show_usage(argv[0]);
+		return make_rune(argv[2]);
+	}
+
 	show_usage(argv[0]);
 }