--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/app/src/main/java/ch/ethz/ssh2/crypto/cipher/CTRMode.java	Thu Dec 03 11:23:55 2015 -0800
@@ -0,0 +1,57 @@
+/*
+ * Copyright (c) 2006-2011 Christian Plattner. All rights reserved.
+ * Please refer to the LICENSE.txt for licensing details.
+ */
+package ch.ethz.ssh2.crypto.cipher;
+
+/**
+ * This is CTR mode as described in draft-ietf-secsh-newmodes-XY.txt
+ *
+ * @author Christian Plattner
+ * @version 2.50, 03/15/10
+ */
+public class CTRMode implements BlockCipher {
+    byte[] X;
+    byte[] Xenc;
+
+    BlockCipher bc;
+    int blockSize;
+    boolean doEncrypt;
+
+    int count = 0;
+
+    public void init(boolean forEncryption, byte[] key) {
+    }
+
+    public CTRMode(BlockCipher tc, byte[] iv, boolean doEnc) throws IllegalArgumentException {
+        bc = tc;
+        blockSize = bc.getBlockSize();
+        doEncrypt = doEnc;
+
+        if (blockSize != iv.length)
+            throw new IllegalArgumentException("IV must be " + blockSize + " bytes long! (currently " + iv.length + ")");
+
+        X = new byte[blockSize];
+        Xenc = new byte[blockSize];
+        System.arraycopy(iv, 0, X, 0, blockSize);
+    }
+
+    public final int getBlockSize() {
+        return blockSize;
+    }
+
+    public final void transformBlock(byte[] src, int srcoff, byte[] dst, int dstoff) {
+        bc.transformBlock(X, 0, Xenc, 0);
+
+        for (int i = 0; i < blockSize; i++) {
+            dst[dstoff + i] = (byte)(src[srcoff + i] ^ Xenc[i]);
+        }
+
+        for (int i = (blockSize - 1); i >= 0; i--) {
+            X[i]++;
+
+            if (X[i] != 0)
+                break;
+        }
+    }
+}