1 files changed, 119 insertions, 0 deletions
diff --git a/src/timedata.cpp b/src/timedata.cpp
new file mode 100644
index 000000000..25fc49412
--- /dev/null
+++ b/src/timedata.cpp
@@ -0,0 +1,119 @@
+// Copyright (c) 2014-2015 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#if defined(HAVE_CONFIG_H)
+#include "config/bitcoin-config.h"
+#endif
+
+#include "timedata.h"
+
+#include "netaddress.h"
+#include "sync.h"
+#include "ui_interface.h"
+#include "util.h"
+#include "utilstrencodings.h"
+
+#include <boost/foreach.hpp>
+
+using namespace std;
+
+static CCriticalSection cs_nTimeOffset;
+static int64_t nTimeOffset = 0;
+
+/**
+ * "Never go to sea with two chronometers; take one or three."
+ * Our three time sources are:
+ *  - System clock
+ *  - Median of other nodes clocks
+ *  - The user (asking the user to fix the system clock if the first two disagree)
+ */
+int64_t GetTimeOffset()
+{
+    LOCK(cs_nTimeOffset);
+    return nTimeOffset;
+}
+
+int64_t GetAdjustedTime()
+{
+    return GetTime() + GetTimeOffset();
+}
+
+static int64_t abs64(int64_t n)
+{
+    return (n >= 0 ? n : -n);
+}
+
+#define BITCOIN_TIMEDATA_MAX_SAMPLES 200
+
+void AddTimeData(const CNetAddr& ip, int64_t nOffsetSample)
+{
+    LOCK(cs_nTimeOffset);
+    // Ignore duplicates
+    static set<CNetAddr> setKnown;
+    if (setKnown.size() == BITCOIN_TIMEDATA_MAX_SAMPLES)
+        return;
+    if (!setKnown.insert(ip).second)
+        return;
+
+    // Add data
+    static CMedianFilter<int64_t> vTimeOffsets(BITCOIN_TIMEDATA_MAX_SAMPLES, 0);
+    vTimeOffsets.input(nOffsetSample);
+    LogPrint("net","added time data, samples %d, offset %+d (%+d minutes)\n", vTimeOffsets.size(), nOffsetSample, nOffsetSample/60);
+
+    // There is a known issue here (see issue #4521):
+    //
+    // - The structure vTimeOffsets contains up to 200 elements, after which
+    // any new element added to it will not increase its size, replacing the
+    // oldest element.
+    //
+    // - The condition to update nTimeOffset includes checking whether the
+    // number of elements in vTimeOffsets is odd, which will never happen after
+    // there are 200 elements.
+    //
+    // But in this case the 'bug' is protective against some attacks, and may
+    // actually explain why we've never seen attacks which manipulate the
+    // clock offset.
+    //
+    // So we should hold off on fixing this and clean it up as part of
+    // a timing cleanup that strengthens it in a number of other ways.
+    //
+    if (vTimeOffsets.size() >= 5 && vTimeOffsets.size() % 2 == 1)
+    {
+        int64_t nMedian = vTimeOffsets.median();
+        std::vector<int64_t> vSorted = vTimeOffsets.sorted();
+        // Only let other nodes change our time by so much
+        if (abs64(nMedian) <= std::max<int64_t>(0, GetArg("-maxtimeadjustment", DEFAULT_MAX_TIME_ADJUSTMENT)))
+        {
+            nTimeOffset = nMedian;
+        }
+        else
+        {
+            nTimeOffset = 0;
+
+            static bool fDone;
+            if (!fDone)
+            {
+                // If nobody has a time different than ours but within 5 minutes of ours, give a warning
+                bool fMatch = false;
+                BOOST_FOREACH(int64_t nOffset, vSorted)
+                    if (nOffset != 0 && abs64(nOffset) < 5 * 60)
+                        fMatch = true;
+
+                if (!fMatch)
+                {
+                    fDone = true;
+                    string strMessage = strprintf(_("Please check that your computer's date and time are correct! If your clock is wrong, %s will not work properly."), _(PACKAGE_NAME));
+                    strMiscWarning = strMessage;
+                    uiInterface.ThreadSafeMessageBox(strMessage, "", CClientUIInterface::MSG_WARNING);
+                }
+            }
+        }
+        
+        BOOST_FOREACH(int64_t n, vSorted)
+            LogPrint("net", "%+d  ", n);
+        LogPrint("net", "|  ");
+        
+        LogPrint("net", "nTimeOffset = %+d  (%+d minutes)\n", nTimeOffset, nTimeOffset/60);
+    }
+}