Added crypto random-number generator

base/rand_util_win.cc

 // Copyright (c) 2008 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/rand_util.h"
 
 #include <stdlib.h>
 
 #include "base/basictypes.h"
 #include "base/logging.h"
 
 namespace {
 
 uint32 RandUint32() {
   uint32 number;
   CHECK_EQ(rand_s(&number), 0);
   return number;
 }
 
 }  // namespace
 
 namespace base {
 
+// NOTE: This function must be cryptographically secure. crypto/ relies on this.
 uint64 RandUint64() {
   uint32 first_half = RandUint32();
   uint32 second_half = RandUint32();
   return (static_cast<uint64>(first_half) << 32) + second_half;
 }
 
 }  // namespace base