Implement audiowmark gen-key command.

Signed-off-by: Stefan Westerfeld <stefan@space.twc.de>

src/TODO

+key:
+- --key loading
+- multiple values per block
+- avoid reroll in up_down generation
+- move shuffle function to Random class
+
 possible improvements:
 - dynamic bit strength
 - mp3 support with libmad

src/audiowmark.cc

@@ -56,6 +56,9 @@ print_usage()
   printf ("  * compute bit error rate for decoding with original file\n");
   printf ("    audiowmark cmp-delta <input_wav> <watermarked_wav> <message_hex>\n");
   printf ("\n");
+  printf ("  * generate 128-bit watermarking key, to be used with --key option\n");
+  printf ("    audiowmark gen-key <key_file>\n");
+  printf ("\n");
   printf ("Global options:\n");
   printf ("  --frame-size          frame size (must be power of 2)     [%zd]\n", Params::frame_size);
   printf ("  --frames-per-bit      number of frames per bit            [%d]\n",  Params::frames_per_bit);
@@ -884,6 +887,20 @@ get_snr (const string& origfile, const string& wmfile)
   return 0;
 }
 
+int
+gen_key (const string& outfile)
+{
+  FILE *f = fopen (outfile.c_str(), "w");
+  if (!f)
+    {
+      fprintf (stderr, "audiowmark: error writing to file %s\n", outfile.c_str());
+      return 1;
+    }
+  fprintf (f, "# watermarking key for audiowmark\n\nkey %s\n", Random::gen_key().c_str());
+  fclose (f);
+  return 0;
+}
+
 int
 main (int argc, char **argv)
 {
@@ -928,9 +945,13 @@ main (int argc, char **argv)
     {
       return get_watermark_delta (argv[2], argv[3], argv[4]);
     }
+  else if (op == "gen-key" && argc == 3)
+    {
+      return gen_key (argv[2]);
+    }
   else
     {
-      fprintf (stderr, "audiowmark: error parsing commandline args\n");
+      fprintf (stderr, "audiowmark: error parsing commandline args (use audiowmark -h)\n");
       return 1;
     }
 }

src/random.cc

 #include "random.hh"
 
+using std::string;
+
 static std::vector<unsigned char> aes_key (16);
 static constexpr auto             GCRY_CIPHER = GCRY_CIPHER_AES128;
 
@@ -123,3 +125,19 @@ Random::set_global_test_key (uint64_t key)
 {
   uint64_to_buffer (key, &aes_key[0]);
 }
+
+std::string
+Random::gen_key()
+{
+  unsigned char key[16];
+  gcry_randomize (key, 16, /* long term key material strength */ GCRY_VERY_STRONG_RANDOM);
+  string s;
+  for (auto k : key)
+    {
+      char buffer[256];
+
+      sprintf (buffer, "%02x", k);
+      s += buffer;
+    }
+  return s;
+}

src/random.hh

@@ -5,6 +5,7 @@
 #include <stdint.h>
 
 #include <vector>
+#include <string>
 
 class Random
 {
@@ -33,7 +34,8 @@ public:
   ~Random();
   uint64_t operator()();
 
-  static void set_global_test_key (uint64_t seed);
+  static void        set_global_test_key (uint64_t seed);
+  static std::string gen_key();
 };
 
 #endif /* AUDIOWMARK_RANDOM_HH */