Improve pool seeding during startup:

* When starting up, we no longer rely just on the standard
  system RNG to generate entropy: we attempt to squeeze some
  from the execution state, and to recover any entropy that
  we had previously stored.

* When shutting down, if sufficient entropy has been accumulated
  attempt to store it for future use.

src/ripple/app/main/Application.cpp

@@ -62,6 +62,7 @@
 #include <ripple/validators/make_Manager.h>
 #include <ripple/unity/git_id.h>
 #include <ripple/websocket/MakeServer.h>
+#include <ripple/crypto/RandomNumbers.h>
 #include <beast/asio/io_latency_probe.h>
 #include <beast/module/core/text/LexicalCast.h>
 #include <beast/module/core/thread/DeadlineTimer.h>
@@ -286,6 +287,7 @@ public:
     std::unique_ptr <Validations> mValidations;
     std::unique_ptr <LoadManager> m_loadManager;
     beast::DeadlineTimer m_sweepTimer;
+    beast::DeadlineTimer m_entropyTimer;
 
     std::unique_ptr <DatabaseCon> mRpcDB;
     std::unique_ptr <DatabaseCon> mTxnDB;
@@ -408,6 +410,8 @@ public:
 
         , m_sweepTimer (this)
 
+        , m_entropyTimer (this)
+
         , m_signals(get_io_service(), SIGINT)
 
         , m_resolver (ResolverAsio::New (get_io_service(), m_logs.journal("Resolver")))
@@ -857,6 +861,7 @@ public:
         m_journal.info << "Application starting. Build is " << gitCommitID();
 
         m_sweepTimer.setExpiration (10);
+        m_entropyTimer.setRecurringExpiration (300);
 
         m_io_latency_sampler.start();
 
@@ -887,6 +892,8 @@ public:
 
         m_sweepTimer.cancel ();
 
+        m_entropyTimer.cancel ();
+
         mValidations->flush ();
 
         RippleAddress::clearCache ();
@@ -952,6 +959,12 @@ public:
 
     void onDeadlineTimer (beast::DeadlineTimer& timer)
     {
+        if (timer == m_entropyTimer)
+        {
+            add_entropy (nullptr, 0);
+            return;
+        }
+
         if (timer == m_sweepTimer)
         {
             // VFALCO TODO Move all this into doSweep

src/ripple/app/main/Main.cpp

@@ -41,6 +41,7 @@
 #include <boost/program_options.hpp>
 #include <cstdlib>
 #include <thread>
+#include <utility>
 
 #if defined(BEAST_LINUX) || defined(BEAST_MAC) || defined(BEAST_BSD)
 #include <sys/resource.h>
@@ -67,6 +68,13 @@ void setupServer ()
     getApp().setup ();
 }
 
+boost::filesystem::path
+getEntropyFile()
+{
+    return boost::filesystem::path (
+        getConfig().legacy("database_path")) / "random.seed";
+}
+
 void startServer ()
 {
     //
@@ -93,7 +101,11 @@ void startServer ()
         }
     }
 
-    getApp().run ();                 // Blocks till we get a stop RPC.
+    // Block until we get a stop RPC.
+    getApp().run ();
+
+    // Try to write out some entropy to use the next time we start.
+    stir_entropy (getEntropyFile ().string ());
 }
 
 void printHelp (const po::options_description& desc)
@@ -258,8 +270,29 @@ int run (int argc, char** argv)
     po::positional_options_description p;
     p.add ("parameters", -1);
 
-    // Seed the RNG early
-    add_entropy ();
+    {
+        // We want to seed the RNG early. We acquire a small amount of
+        // questionable quality entropy from the current time and our
+        // environment block which will get stirred into the RNG pool
+        // along with high-quality entropy from the system.
+        struct entropy_t
+        {
+            std::uint64_t timestamp;
+            std::size_t tid;
+            std::uintptr_t ptr[4];
+        };
+
+        auto entropy = std::make_unique<entropy_t> ();
+
+        entropy->timestamp = beast::Time::currentTimeMillis ();
+        entropy->tid = std::hash <std::thread::id>() (std::this_thread::get_id ());
+        entropy->ptr[0] = reinterpret_cast<std::uintptr_t>(entropy.get ());
+        entropy->ptr[1] = reinterpret_cast<std::uintptr_t>(&argc);
+        entropy->ptr[2] = reinterpret_cast<std::uintptr_t>(argv);
+        entropy->ptr[3] = reinterpret_cast<std::uintptr_t>(argv[0]);
+
+        add_entropy (entropy.get (), sizeof (entropy_t));
+    }
 
     if (!iResult)
     {
@@ -346,6 +379,9 @@ int run (int argc, char** argv)
             getConfig ().RUN_STANDALONE = true;
             getConfig ().LEDGER_HISTORY = 0;
         }
+
+        // Use any previously available entropy to stir the pool
+        stir_entropy (getEntropyFile ().string ());
     }
 
     if (vm.count ("start")) getConfig ().START_UP = Config::FRESH;

src/ripple/core/Config.h

@@ -124,6 +124,9 @@ public:
     /** Returns the full path and filename of the debug log file. */
     boost::filesystem::path getDebugLogFile () const;
 
+    /** Returns the full path and filename of the entropy seed file. */
+    boost::filesystem::path getEntropyFile () const;
+
     // DEPRECATED
     boost::filesystem::path CONFIG_FILE; // used by UniqueNodeList
 private:

src/ripple/crypto/RandomNumbers.h

@@ -20,10 +20,21 @@
 #ifndef RIPPLE_CRYPTO_RANDOMNUMBERS_H_INCLUDED
 #define RIPPLE_CRYPTO_RANDOMNUMBERS_H_INCLUDED
 
+#include <string>
 #include <beast/cxx14/type_traits.h> // <type_traits>
 
 namespace ripple {
 
+/** Stir the RNG using entropy from stable storage.
+
+    @param file the file from which state is loaded and into
+           which it is saved.
+
+    @return true if the pool has sufficient entropy; false
+            otherwise.
+*/
+bool stir_entropy (std::string file);
+
 /** Adds entropy to the RNG pool.
 
     @param buffer An optional buffer that contains random data.

src/ripple/crypto/impl/RandomNumbers.cpp

@@ -26,6 +26,18 @@
 
 namespace ripple {
 
+bool stir_entropy (std::string file)
+{
+    // First, we attempt to stir any existing saved entropy
+    // into the pool: no use letting it go to waste.
+    RAND_load_file (file.c_str (), 1024);
+
+    // And now, we extract some entropy out, and save it for
+    // the future. If the quality of the entropy isn't great
+    // then we let the user know.
+    return RAND_write_file (file.c_str ()) != -1;
+}
+
 void add_entropy (void* buffer, int count)
 {
     assert (buffer == nullptr || count != 0);
@@ -35,7 +47,7 @@ void add_entropy (void* buffer, int count)
     if (buffer != nullptr && count != 0)
         RAND_add (buffer, count, count / 4.0);
 
-    // Try to add a bit more entropy from the system
+    // And try to add some entropy from the system
     unsigned int rdbuf[32];
 
     std::random_device rd;