From 81a4f3ced09eb0754101eac492173119a7869598 Mon Sep 17 00:00:00 2001
From: Chocobo1 <Chocobo1@users.noreply.github.com>
Date: Fri, 6 Apr 2018 17:43:42 +0800
Subject: [PATCH] Use RNG provided by OS

The general consensus is to use random facility provided by OS instead
of using other software random generators.
---
 src/base/utils/random.cpp | 124 +++++++++++++++++++++++++++++---------
 src/base/utils/random.h   |   3 +-
 2 files changed, 96 insertions(+), 31 deletions(-)

diff --git a/src/base/utils/random.cpp b/src/base/utils/random.cpp
index add0b4e16..fac913227 100644
--- a/src/base/utils/random.cpp
+++ b/src/base/utils/random.cpp
@@ -29,47 +29,113 @@
 
 #include "random.h"
 
-#include <cassert>
-#include <chrono>
+#include <limits>
 #include <random>
 
 #include <QtGlobal>
 
-#ifdef Q_OS_MAC
-#include <QThreadStorage>
+#ifdef Q_OS_WIN
+#ifndef NOMINMAX
+#define NOMINMAX
+#endif
+#include <Windows.h>
+#include <Ntsecapi.h>
+#else  // Q_OS_WIN
+#include <cstdio>
 #endif
 
-// on some platform `std::random_device` may generate the same number sequence
-static bool hasTrueRandomDevice{ std::random_device{}() != std::random_device{}() };
+#include "misc.h"
 
-uint32_t Utils::Random::rand(const uint32_t min, const uint32_t max)
+namespace
 {
-#ifdef Q_OS_MAC  // workaround for Apple xcode: https://stackoverflow.com/a/29929949
-    static QThreadStorage<std::mt19937> generator;
-    if (!generator.hasLocalData())
-        generator.localData().seed(
-            hasTrueRandomDevice
-            ? std::random_device{}()
-            : (std::random_device::result_type) std::chrono::system_clock::now().time_since_epoch().count()
-        );
-#else
-    static thread_local std::mt19937 generator{
-        hasTrueRandomDevice
-        ? std::random_device{}()
-        : static_cast<std::random_device::result_type>(std::chrono::system_clock::now().time_since_epoch().count())
+#ifdef Q_OS_WIN
+    class RandomLayer
+    {
+    // need to satisfy UniformRandomBitGenerator requirements
+    public:
+        using result_type = uint32_t;
+
+        RandomLayer()
+            : m_rtlGenRandom {Utils::Misc::loadWinAPI<PRTLGENRANDOM>("Advapi32.dll", "SystemFunction036")}
+        {
+            if (!m_rtlGenRandom)
+                qFatal("Failed to load RtlGenRandom()");
+        }
+
+        static constexpr result_type min()
+        {
+            return std::numeric_limits<result_type>::min();
+        }
+
+        static constexpr result_type max()
+        {
+            return std::numeric_limits<result_type>::max();
+        }
+
+        result_type operator()()
+        {
+            result_type buf = 0;
+            const bool result = m_rtlGenRandom(&buf, sizeof(buf));
+            if (!result)
+                qFatal("RtlGenRandom() failed");
+
+            return buf;
+        }
+
+    private:
+        using PRTLGENRANDOM = BOOLEAN (WINAPI *)(PVOID, ULONG);
+        const PRTLGENRANDOM m_rtlGenRandom;
+    };
+#else  // Q_OS_WIN
+    class RandomLayer
+    {
+    // need to satisfy UniformRandomBitGenerator requirements
+    public:
+        using result_type = uint32_t;
+
+        RandomLayer()
+            : m_randDev {fopen("/dev/urandom", "rb")}
+        {
+            if (!m_randDev)
+                qFatal("Failed to open /dev/urandom");
+        }
+
+        ~RandomLayer()
+        {
+            fclose(m_randDev);
+        }
+
+        static constexpr result_type min()
+        {
+            return std::numeric_limits<result_type>::min();
+        }
+
+        static constexpr result_type max()
+        {
+            return std::numeric_limits<result_type>::max();
+        }
+
+        result_type operator()() const
+        {
+            result_type buf = 0;
+            if (fread(&buf, sizeof(buf), 1, m_randDev) != 1)
+                qFatal("Read /dev/urandom error");
+
+            return buf;
+        }
+
+    private:
+        FILE *m_randDev;
     };
 #endif
+}
 
-    // better replacement for `std::rand`, don't use this for real cryptography application
-    // min <= returned_value <= max
-    assert(min <= max);
+uint32_t Utils::Random::rand(const uint32_t min, const uint32_t max)
+{
+    static RandomLayer layer;
 
-    // new distribution is cheap: http://stackoverflow.com/a/19036349
+    // new distribution is cheap: https://stackoverflow.com/a/19036349
     std::uniform_int_distribution<uint32_t> uniform(min, max);
 
-#ifdef Q_OS_MAC
-    return uniform(generator.localData());
-#else
-    return uniform(generator);
-#endif
+    return uniform(layer);
 }
diff --git a/src/base/utils/random.h b/src/base/utils/random.h
index d4198deca..106d0b90f 100644
--- a/src/base/utils/random.h
+++ b/src/base/utils/random.h
@@ -31,13 +31,12 @@
 #define UTILS_RANDOM_H
 
 #include <cstdint>
-#include <cstdlib>
 
 namespace Utils
 {
     namespace Random
     {
-        uint32_t rand(uint32_t min = 0, uint32_t max = UINT32_MAX);
+        uint32_t rand(const uint32_t min = 0, const uint32_t max = UINT32_MAX);
     }
 }