Fix fread check for reading randomness (#384)

* Fix fread check for reading randomness

Fallback CSPRNG on generic UNIX will read `urandom` for randomness. The read has a bug where if `fread` reads say 10 bytes but the size is 32. The buffer is only partially updated and returned successful.

This patch ensures the fallback read returns success only when the buffer is fully filled.

* Fix fread condition to check for equality

* Use microseconds

Author: marty1885

trantor/utils/Utilities.cc

@@ -441,7 +441,7 @@ static bool systemRandomBytes(void *ptr, size_t size)
         LOG_FATAL << "Failed to open /dev/urandom for randomness";
         abort();
     }
-    if (fread(ptr, 1, size, fptr.get()) != 0)
+    if (fread(ptr, 1, size, fptr.get()) == size)
         return true;
 #endif
     return false;
@@ -533,9 +533,9 @@ bool secureRandomBytes(void *data, size_t len)
     auto now = chrono::steady_clock::now();
     // the proposed algorithm uses the time in nanoseconds, but we don't have a
     // way to read it (yet) not C++ provided a standard way to do it. Falling
-    // back to milliseconds. This along with additional entropy is hopefully
+    // back to microseconds. This along with additional entropy is hopefully
     // good enough.
-    state.time = chrono::time_point_cast<chrono::milliseconds>(now)
+    state.time = chrono::time_point_cast<chrono::microseconds>(now)
                      .time_since_epoch()
                      .count();
     // `now` lives on the stack, so address in each call _may_ be different.