base/rand_util_win.cc

   1 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #include "base/rand_util.h"
   6
   7 #include <windows.h>
   8
   9 // #define needed to link in RtlGenRandom(), a.k.a. SystemFunction036.  See the
  10 // "Community Additions" comment on MSDN here:
  11 // http://msdn.microsoft.com/en-us/library/windows/desktop/aa387694.aspx
  12 #define SystemFunction036 NTAPI SystemFunction036
  13 #include <NTSecAPI.h>
  14 #undef SystemFunction036
  15
  16 #include <algorithm>
  17 #include <limits>
  18
  19 #include "base/logging.h"
  20
  21 namespace base {
  22
  23 // NOTE: This function must be cryptographically secure. http://crbug.com/140076
  24 uint64 RandUint64() {
  25   uint64 number;
  26   RandBytes(&number, sizeof(number));
  27   return number;
  28 }
  29
  30 void RandBytes(void* output, size_t output_length) {
  31   char* output_ptr = static_cast<char*>(output);
  32   while (output_length > 0) {
  33     const ULONG output_bytes_this_pass = static_cast<ULONG>(std::min(
  34         output_length, static_cast<size_t>(std::numeric_limits<ULONG>::max())));
  35     const bool success =
  36         RtlGenRandom(output_ptr, output_bytes_this_pass) != FALSE;
  37     CHECK(success);
  38     output_length -= output_bytes_this_pass;
  39     output_ptr += output_bytes_this_pass;
  40   }
  41 }
  42
  43 }  // namespace base