hsmtool: implement checkhsm.

This gives a nice way to ensure your secret is the correct one.

Also, we don't need to suppress VALGRIND for this test, now the output
races are fixed.

Changelog-Added: `hsmtool`: new command `checkhsm` to check BIP39 passphrase against hsm_secret.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

doc/lightning-hsmtool.8.md

@@ -51,6 +51,9 @@ Specify *password* if the `hsm_secret` is encrypted.
 **generatehsm** *hsm\_secret\_path*
 Generates a new hsm_secret using BIP39.
 
+**checkhsm** *hsm\_secret\_path*
+Checks that hsm_secret matchs a BIP39 pass phrase.
+
  **dumponchaindescriptors** *hsm_secret* \[*password*\] \[*network*\]
 Dump output descriptors for our onchain wallet.
 The descriptors can be used by external services to be able to generate

tests/test_wallet.py

@@ -1218,7 +1218,6 @@ def test_hsmtool_dump_descriptors(node_factory, bitcoind):
     assert len(bitcoind.rpc.listunspent(1, 1, [addr])) == 1
 
 
-@unittest.skipIf(VALGRIND, "It does not play well with prompt and key derivation.")
 def test_hsmtool_generatehsm(node_factory):
     l1 = node_factory.get_node(start=False)
     hsm_path = os.path.join(l1.daemon.lightning_dir, TEST_NETWORK,
@@ -1242,9 +1241,48 @@ def test_hsmtool_generatehsm(node_factory):
               "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"))
-    hsmtool.proc.wait(WAIT_TIMEOUT)
+    assert hsmtool.proc.wait(WAIT_TIMEOUT) == 0
     hsmtool.is_in_log(r"New hsm_secret file created")
 
+    # Check should pass.
+    hsmtool = HsmTool(node_factory.directory, "checkhsm", hsm_path)
+    master_fd, slave_fd = os.openpty()
+    hsmtool.start(stdin=slave_fd)
+    hsmtool.wait_for_log(r"Enter your passphrase:")
+    write_all(master_fd, "This is actually not a passphrase\n".encode("utf-8"))
+    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"))
+    assert hsmtool.proc.wait(WAIT_TIMEOUT) == 0
+    hsmtool.is_in_log(r"OK")
+
+    # Wrong mnemonic will fail.
+    master_fd, slave_fd = os.openpty()
+    hsmtool.start(stdin=slave_fd)
+    hsmtool.wait_for_log(r"Enter your passphrase:")
+    write_all(master_fd, "This is actually not a passphrase\n".encode("utf-8"))
+    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, "abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon about\n".encode("utf-8"))
+    assert hsmtool.proc.wait(WAIT_TIMEOUT) == 5
+    hsmtool.is_in_log(r"resulting hsm_secret did not match")
+
+    # Wrong passphrase will fail.
+    master_fd, slave_fd = os.openpty()
+    hsmtool.start(stdin=slave_fd)
+    hsmtool.wait_for_log(r"Enter your passphrase:")
+    write_all(master_fd, "This is actually not a passphrase \n".encode("utf-8"))
+    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"))
+    assert hsmtool.proc.wait(WAIT_TIMEOUT) == 5
+    hsmtool.is_in_log(r"resulting hsm_secret did not match")
+
     # We can start the node with this hsm_secret
     l1.start()
     assert l1.info['id'] == '02244b73339edd004bc6dfbb953a87984c88e9e7c02ca14ef6ec593ca6be622ba7'

tools/hsmtool.c

@@ -39,6 +39,7 @@ static void show_usage(const char *progname)
 	printf("	- guesstoremote <P2WPKH address> <node id> <tries> "
 	       "<path/to/hsm_secret>\n");
 	printf("	- generatehsm <path/to/new/hsm_secret>\n");
+	printf("	- checkhsm <path/to/new/hsm_secret>\n");
 	printf("	- dumponchaindescriptors <path/to/hsm_secret> [network]\n");
 	exit(0);
 }
@@ -595,6 +596,60 @@ static int dumponchaindescriptors(const char *hsm_secret_path, const char *old_p
 	return 0;
 }
 
+static int check_hsm(const char *hsm_secret_path)
+{
+	char mnemonic[BIP39_WORDLIST_LEN];
+	struct secret hsm_secret;
+	u8 bip32_seed[BIP39_SEED_LEN_512];
+	size_t bip32_seed_len;
+	int exit_code;
+	char *passphrase, *err;
+
+	/* This checks the file existence, too. */
+	if (hsm_secret_is_encrypted(hsm_secret_path)) {
+		char *passwd;
+
+		printf("Enter hsm_secret password:\n");
+		fflush(stdout);
+		passwd = read_stdin_pass_with_exit_code(&err, &exit_code);
+		if (!passwd)
+			errx(exit_code, "%s", err);
+
+		if (sodium_init() == -1)
+			errx(ERROR_LIBSODIUM,
+			     "Could not initialize libsodium. Not enough entropy ?");
+
+		get_encrypted_hsm_secret(&hsm_secret, hsm_secret_path, passwd);
+		/* Once the encryption key derived, we don't need it anymore. */
+		free(passwd);
+	} else
+		get_hsm_secret(&hsm_secret, hsm_secret_path);
+
+	printf("Warning: remember that different passphrases yield different "
+	       "bitcoin wallets.\n");
+	printf("If left empty, no password is used (echo is disabled).\n");
+	printf("Enter your passphrase: \n");
+	fflush(stdout);
+	passphrase = read_stdin_pass_with_exit_code(&err, &exit_code);
+	if (!passphrase)
+		errx(exit_code, "%s", err);
+	if (strlen(passphrase) == 0) {
+		free(passphrase);
+		passphrase = NULL;
+	}
+
+	read_mnemonic(mnemonic);
+	if (bip39_mnemonic_to_seed(mnemonic, passphrase, bip32_seed, sizeof(bip32_seed), &bip32_seed_len) != WALLY_OK)
+		errx(ERROR_LIBWALLY, "Unable to derive BIP32 seed from BIP39 mnemonic");
+
+	/* We only use first 32 bytes */
+	if (memcmp(bip32_seed, hsm_secret.data, sizeof(hsm_secret.data)) != 0)
+		errx(ERROR_KEYDERIV, "resulting hsm_secret did not match");
+
+	printf("OK\n");
+	return 0;
+}
+
 int main(int argc, char *argv[])
 {
 	const char *method;
@@ -682,5 +737,11 @@ int main(int argc, char *argv[])
 		return dumponchaindescriptors(argv[2], NULL, is_testnet);
 	}
 
+	if (streq(method, "checkhsm")) {
+		if (argc < 3)
+			show_usage(argv[0]);
+		return check_hsm(argv[2]);
+	}
+
 	show_usage(argv[0]);
 }