1 files changed, 91 insertions, 0 deletions
diff --git a/libraries/spongycastle/core/src/main/java/org/spongycastle/crypto/tls/DTLSReplayWindow.java b/libraries/spongycastle/core/src/main/java/org/spongycastle/crypto/tls/DTLSReplayWindow.java
new file mode 100644
index 000000000..1ce21b5b3
--- /dev/null
+++ b/libraries/spongycastle/core/src/main/java/org/spongycastle/crypto/tls/DTLSReplayWindow.java
@@ -0,0 +1,91 @@
+package org.spongycastle.crypto.tls;
+
+/**
+ * RFC 4347 4.1.2.5 Anti-replay
+ * <p/>
+ * Support fast rejection of duplicate records by maintaining a sliding receive window
+ */
+class DTLSReplayWindow
+{
+
+    private static final long VALID_SEQ_MASK = 0x0000FFFFFFFFFFFFL;
+
+    private static final long WINDOW_SIZE = 64L;
+
+    private long latestConfirmedSeq = -1;
+    private long bitmap = 0;
+
+    /**
+     * Check whether a received record with the given sequence number should be rejected as a duplicate.
+     *
+     * @param seq the 48-bit DTLSPlainText.sequence_number field of a received record.
+     * @return true if the record should be discarded without further processing.
+     */
+    boolean shouldDiscard(long seq)
+    {
+        if ((seq & VALID_SEQ_MASK) != seq)
+        {
+            return true;
+        }
+
+        if (seq <= latestConfirmedSeq)
+        {
+            long diff = latestConfirmedSeq - seq;
+            if (diff >= WINDOW_SIZE)
+            {
+                return true;
+            }
+            if ((bitmap & (1L << diff)) != 0)
+            {
+                return true;
+            }
+        }
+
+        return false;
+    }
+
+    /**
+     * Report that a received record with the given sequence number passed authentication checks.
+     *
+     * @param seq the 48-bit DTLSPlainText.sequence_number field of an authenticated record.
+     */
+    void reportAuthenticated(long seq)
+    {
+        if ((seq & VALID_SEQ_MASK) != seq)
+        {
+            throw new IllegalArgumentException("'seq' out of range");
+        }
+
+        if (seq <= latestConfirmedSeq)
+        {
+            long diff = latestConfirmedSeq - seq;
+            if (diff < WINDOW_SIZE)
+            {
+                bitmap |= (1L << diff);
+            }
+        }
+        else
+        {
+            long diff = seq - latestConfirmedSeq;
+            if (diff >= WINDOW_SIZE)
+            {
+                bitmap = 1;
+            }
+            else
+            {
+                bitmap <<= (int)diff;        // for earlier JDKs
+                bitmap |= 1;
+            }
+            latestConfirmedSeq = seq;
+        }
+    }
+
+    /**
+     * When a new epoch begins, sequence numbers begin again at 0
+     */
+    void reset()
+    {
+        latestConfirmedSeq = -1;
+        bitmap = 0;
+    }
+}