Add genpass: a tool to generate passwordsHEADorigin/mastermaster

1 files changed, 151 insertions, 0 deletions

diff --git a/genpass.c b/genpass.c
new file mode 100644
index 0000000..623eecb
--- /dev/null
+++ b/genpass.c
@@ -0,0 +1,151 @@
+/*
+ * genpass.c: password generator
+ *
+ * Copyright (c) 2025, Přemysl Eric Janouch <p@janouch.name>
+ *
+ * Permission to use, copy, modify, and/or distribute this software for any
+ * purpose with or without fee is hereby granted.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
+ * SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
+ * OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
+ * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ *
+ */
+
+#include "config.h"
+#undef PROGRAM_NAME
+#define PROGRAM_NAME "genpass"
+#include "liberty/liberty.c"
+
+static struct str
+parse_group (const char *group)
+{
+	bool present[0x100] = {};
+	for (size_t i = 0; group[i]; i++)
+	{
+		unsigned char c = group[i];
+		if (!i || c != '-' || !group[i + 1])
+			present[c] = true;
+		else if (group[i + 1] < group[i - 1])
+			exit_fatal ("character ranges must be increasing");
+		else
+			for (c = group[i - 1]; ++c <= group[i + 1]; )
+				present[c] = true;
+	}
+
+	struct str alphabet = str_make ();
+	for (size_t i = 1; i < N_ELEMENTS (present); i++)
+		if (present[i])
+			str_append_c (&alphabet, i);
+	if (!alphabet.len)
+		exit_fatal ("empty group");
+	return alphabet;
+}
+
+static void
+parse_program_arguments (int argc, char **argv,
+	unsigned long *length, struct strv *groups, struct str *alphabet)
+{
+	static const struct opt opts[] =
+	{
+		{ 'l', "length", "CHARACTERS", 0, "set password length" },
+		{ 'd', "debug", NULL, 0, "run in debug mode" },
+		{ 'h', "help", NULL, 0, "display this help and exit" },
+		{ 'V', "version", NULL, 0, "output version information and exit" },
+		{ 0, NULL, NULL, 0, NULL }
+	};
+
+	struct opt_handler oh =
+		opt_handler_make (argc, argv, opts, "GROUP...", "Password generator.");
+
+	int c;
+	while ((c = opt_handler_get (&oh)) != -1)
+	switch (c)
+	{
+	case 'l':
+		if (!xstrtoul (length, optarg, 10) || *length <= 0)
+			print_fatal ("invalid length argument");
+		break;
+	case 'd':
+		g_debug_mode = true;
+		break;
+	case 'h':
+		opt_handler_usage (&oh, stdout);
+		exit (EXIT_SUCCESS);
+	case 'V':
+		printf (PROGRAM_NAME " " PROGRAM_VERSION "\n");
+		exit (EXIT_SUCCESS);
+	default:
+		print_error ("wrong options");
+		opt_handler_usage (&oh, stderr);
+		exit (EXIT_FAILURE);
+	}
+
+	argc -= optind;
+	argv += optind;
+
+	for (int i = 0; i < argc; i++)
+	{
+		struct str alphabet = parse_group (argv[i]);
+		strv_append_owned (groups, str_steal (&alphabet));
+	}
+
+	bool present[0x100] = {};
+	for (size_t i = 0; i < groups->len; i++)
+		for (size_t k = 0; groups->vector[i][k]; k++)
+		{
+			unsigned char c = groups->vector[i][k];
+			if (present[c])
+				exit_fatal ("groups are not disjunct");
+			present[c] = true;
+		}
+	for (size_t i = 1; i < N_ELEMENTS (present); i++)
+		if (present[i])
+			str_append_c (alphabet, i);
+
+	if (groups->len > *length)
+		exit_fatal ("the requested length is less than the number of groups");
+	if (!groups->len)
+	{
+		opt_handler_usage (&oh, stderr);
+		exit (EXIT_FAILURE);
+	}
+
+	opt_handler_free (&oh);
+}
+
+int
+main (int argc, char *argv[])
+{
+	unsigned long length = 8;
+	struct strv groups = strv_make ();
+	struct str alphabet = str_make ();
+	parse_program_arguments (argc, argv, &length, &groups, &alphabet);
+
+	unsigned seed = 0;
+	if (!random_bytes (&seed, sizeof seed, NULL))
+		exit_fatal ("failed to initialize random numbers");
+	srand (seed);
+
+	// Select from a joined alphabet, but make sure all groups are represented.
+	struct str candidate = str_make ();
+	while (true)
+	{
+restart:
+		for (size_t i = length; i--; )
+			str_append_c (&candidate, alphabet.str[rand () % alphabet.len]);
+		for (size_t i = 0; i < groups.len; i++)
+			if (!strpbrk (candidate.str, groups.vector[i]))
+			{
+				str_reset (&candidate);
+				goto restart;
+			}
+
+		printf ("%s\n", candidate.str);
+		return 0;
+	}
+}