Provide re-seeding operation for random generator.

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

src/random.cc

@@ -78,57 +78,50 @@ print (const string& label, const vector<unsigned char>& data)
 }
 #endif
 
-Random::Random (uint64_t seed, Stream stream)
+Random::Random (uint64_t start_seed, Stream stream)
 {
   gcrypt_init();
 
-  vector<unsigned char> ctr = get_start_counter (seed, stream);
-
-  // print ("CTR", ctr);
-
   gcry_error_t gcry_ret = gcry_cipher_open (&aes_ctr_cipher, GCRY_CIPHER, GCRY_CIPHER_MODE_CTR, 0);
   die_on_error ("gcry_cipher_open", gcry_ret);
 
   gcry_ret = gcry_cipher_setkey (aes_ctr_cipher, &aes_key[0], aes_key.size());
   die_on_error ("gcry_cipher_setkey", gcry_ret);
 
-  gcry_ret = gcry_cipher_setctr (aes_ctr_cipher, &ctr[0], ctr.size());
-  die_on_error ("gcry_cipher_setctr", gcry_ret);
-}
+  gcry_ret = gcry_cipher_open (&seed_cipher, GCRY_CIPHER, GCRY_CIPHER_MODE_ECB, 0);
+  die_on_error ("gcry_cipher_open", gcry_ret);
 
-Random::~Random()
-{
-  gcry_cipher_close (aes_ctr_cipher);
+  gcry_ret = gcry_cipher_setkey (seed_cipher, &aes_key[0], aes_key.size());
+  die_on_error ("gcry_cipher_setkey", gcry_ret);
+
+  seed (start_seed, stream);
 }
 
-vector<unsigned char>
-Random::get_start_counter (uint64_t seed, Stream stream)
+void
+Random::seed (uint64_t seed, Stream stream)
 {
-  gcry_error_t     gcry_ret;
-  gcry_cipher_hd_t cipher_hd;
-
-  gcry_ret = gcry_cipher_open (&cipher_hd, GCRY_CIPHER, GCRY_CIPHER_MODE_ECB, 0);
-  die_on_error ("gcry_cipher_open", gcry_ret);
-
-  gcry_ret = gcry_cipher_setkey (cipher_hd, &aes_key[0], aes_key.size());
-  die_on_error ("gcry_cipher_setkey", gcry_ret);
+  buffer_pos = 0;
+  buffer.clear();
 
-  vector<unsigned char> cipher_text (16);
-  vector<unsigned char> plain_text (16);
+  unsigned char plain_text[aes_key.size()] = { 0, };
+  unsigned char cipher_text[aes_key.size()];
 
   uint64_to_buffer (seed, &plain_text[0]);
 
   plain_text[8] = uint8_t (stream);
 
-  // print ("SEED", plain_text);
-
-  gcry_ret = gcry_cipher_encrypt (cipher_hd, &cipher_text[0], cipher_text.size(),
-                                             &plain_text[0],  plain_text.size());
+  gcry_error_t gcry_ret = gcry_cipher_encrypt (seed_cipher, &cipher_text[0], aes_key.size(),
+                                                            &plain_text[0],  aes_key.size());
   die_on_error ("gcry_cipher_encrypt", gcry_ret);
 
-  gcry_cipher_close (cipher_hd);
+  gcry_ret = gcry_cipher_setctr (aes_ctr_cipher, &cipher_text[0], aes_key.size());
+  die_on_error ("gcry_cipher_setctr", gcry_ret);
+}
 
-  return cipher_text;
+Random::~Random()
+{
+  gcry_cipher_close (aes_ctr_cipher);
+  gcry_cipher_close (seed_cipher);
 }
 
 void

src/random.hh

@@ -19,12 +19,11 @@ public:
     frame_position = 6
   };
 private:
-  gcry_cipher_hd_t           aes_ctr_cipher;
+  gcry_cipher_hd_t           aes_ctr_cipher = nullptr;
+  gcry_cipher_hd_t           seed_cipher = nullptr;
   std::vector<uint64_t>      buffer;
   size_t                     buffer_pos = 0;
 
-  std::vector<unsigned char> get_start_counter (uint64_t seed, Stream stream);
-
   void die_on_error (const char *func, gcry_error_t error);
 public:
   Random (uint64_t seed, Stream stream);
@@ -39,6 +38,7 @@ public:
     return buffer[buffer_pos++];
   }
   void refill_buffer();
+  void seed (uint64_t seed, Stream stream);
 
   template<class T> void
   shuffle (std::vector<T>& result)