1 files changed, 84 insertions, 0 deletions
diff --git a/crypto/src/tls/DtlsReplayWindow.cs b/crypto/src/tls/DtlsReplayWindow.cs
new file mode 100644
index 000000000..a08114c2a
--- /dev/null
+++ b/crypto/src/tls/DtlsReplayWindow.cs
@@ -0,0 +1,84 @@
+using System;
+
+namespace Org.BouncyCastle.Tls
+{
+    /**
+     * RFC 4347 4.1.2.5 Anti-replay
+     * <p>
+     * Support fast rejection of duplicate records by maintaining a sliding receive window
+     * </p>
+     */
+    internal sealed class DtlsReplayWindow
+    {
+        private const long ValidSeqMask = 0x0000FFFFFFFFFFFFL;
+
+        private const long WindowSize = 64L;
+
+        private long m_latestConfirmedSeq = -1;
+        private ulong m_bitmap = 0;
+
+        /// <summary>Check whether a received record with the given sequence number should be rejected as a duplicate.
+        /// </summary>
+        /// <param name="seq">the 48-bit DTLSPlainText.sequence_number field of a received record.</param>
+        /// <returns>true if the record should be discarded without further processing.</returns>
+        internal bool ShouldDiscard(long seq)
+        {
+            if ((seq & ValidSeqMask) != seq)
+                return true;
+
+            if (seq <= m_latestConfirmedSeq)
+            {
+                long diff = m_latestConfirmedSeq - seq;
+                if (diff >= WindowSize)
+                    return true;
+
+                if ((m_bitmap & (1UL << (int)diff)) != 0)
+                    return true;
+            }
+
+            return false;
+        }
+
+        /// <summary>Report that a received record with the given sequence number passed authentication checks.
+        /// </summary>
+        /// <param name="seq">the 48-bit DTLSPlainText.sequence_number field of an authenticated record.</param>
+        internal void ReportAuthenticated(long seq)
+        {
+            if ((seq & ValidSeqMask) != seq)
+                throw new ArgumentException("out of range", "seq");
+
+            if (seq <= m_latestConfirmedSeq)
+            {
+                long diff = m_latestConfirmedSeq - seq;
+                if (diff < WindowSize)
+                {
+                    m_bitmap |= (1UL << (int)diff);
+                }
+            }
+            else
+            {
+                long diff = seq - m_latestConfirmedSeq;
+                if (diff >= WindowSize)
+                {
+                    m_bitmap = 1;
+                }
+                else
+                {
+                    m_bitmap <<= (int)diff;        // for earlier JDKs
+                    m_bitmap |= 1UL;
+                }
+                m_latestConfirmedSeq = seq;
+            }
+        }
+
+        internal void Reset(long seq)
+        {
+            if ((seq & ValidSeqMask) != seq)
+                throw new ArgumentException("out of range", "seq");
+
+            // Discard future records unless sequence number > 'seq'
+            m_latestConfirmedSeq = seq;
+            m_bitmap = ulong.MaxValue >> (int)System.Math.Max(0, 63 - seq);
+        }
+    }
+}