Revise getRandom facilities

Use one of the following to provide random bytes:
- Windows CryptGenRandom
- Linux getrandom (syscall interface to urandom, without nasty corner
  cases such as file descriptor exhaustion or re-linked /dev/urandom)
- std::device_random (C++ random device, which usually will be urandom)

This also equalizes util::getRandom and SimpleRandomizer (the former
will now use the latter) instead of having essentially two different
PRNG interfaces with potentially different quality.

Closes GH-320

1 files changed, 37 insertions, 10 deletions

diff --git a/src/SimpleRandomizer.h b/src/SimpleRandomizer.h
index fa576306..65ac2094 100644
--- a/src/SimpleRandomizer.h
+++ b/src/SimpleRandomizer.h
@@ -41,30 +41,32 @@
 #include <random>
 
 #ifdef __MINGW32__
-# include <wincrypt.h>
-#endif // __MINGW32__
+#  include <wincrypt.h>
+#endif
 
 namespace aria2 {
 
 class SimpleRandomizer : public Randomizer {
 private:
   static std::unique_ptr<SimpleRandomizer> randomizer_;
+  SimpleRandomizer();
 
+private:
 #ifdef __MINGW32__
-  HCRYPTPROV cryProvider_;
-#else // !__MINGW32__
-  std::minstd_rand eng_;
-#endif //!__MINGW32__
+  HCRYPTPROV provider_;
+#elif defined(HAVE_GETRANDOM_INTERFACE)
+  // Nothing special needed
+#else
+  std::random_device dev_;
+#endif // ! __MINGW32__
 
-  SimpleRandomizer();
 public:
+  typedef std::random_device::result_type result_type;
 
   static const std::unique_ptr<SimpleRandomizer>& getInstance();
 
   virtual ~SimpleRandomizer();
 
-  void init();
-
   /**
    * Returns random number in [0, to).
    */
@@ -72,7 +74,32 @@ public:
 
   void getRandomBytes(unsigned char *buf, size_t len);
 
-  long int operator()(long int to);
+  long int operator()(long int to)
+  {
+    return getRandomNumber(to);
+  }
+
+  result_type operator()()
+  {
+    result_type rv;
+    getRandomBytes(reinterpret_cast<unsigned char*>(&rv), sizeof(rv));
+    return rv;
+  }
+
+  static constexpr result_type min()
+  {
+    return std::numeric_limits<result_type>::min();
+  }
+
+  static constexpr result_type max()
+  {
+    return std::numeric_limits<result_type>::max();
+  }
+
+  static double entropy()
+  {
+    return 0.0;
+  }
 };
 
 } // namespace aria2