| /* CTR.java -- |
| Copyright (C) 2001, 2002, 2006 Free Software Foundation, Inc. |
| |
| This file is a part of GNU Classpath. |
| |
| GNU Classpath is free software; you can redistribute it and/or modify |
| it under the terms of the GNU General Public License as published by |
| the Free Software Foundation; either version 2 of the License, or (at |
| your option) any later version. |
| |
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| WITHOUT ANY WARRANTY; without even the implied warranty of |
| MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
| General Public License for more details. |
| |
| You should have received a copy of the GNU General Public License |
| along with GNU Classpath; if not, write to the Free Software |
| Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 |
| USA |
| |
| Linking this library statically or dynamically with other modules is |
| making a combined work based on this library. Thus, the terms and |
| conditions of the GNU General Public License cover the whole |
| combination. |
| |
| As a special exception, the copyright holders of this library give you |
| permission to link this library with independent modules to produce an |
| executable, regardless of the license terms of these independent |
| modules, and to copy and distribute the resulting executable under |
| terms of your choice, provided that you also meet, for each linked |
| independent module, the terms and conditions of the license of that |
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| exception statement from your version. */ |
| |
| |
| package gnu.javax.crypto.mode; |
| |
| import gnu.java.security.Registry; |
| import gnu.java.security.util.Sequence; |
| import gnu.javax.crypto.cipher.IBlockCipher; |
| |
| import java.util.Arrays; |
| import java.util.Iterator; |
| |
| /** |
| * The implementation of the Counter Mode. |
| * <p> |
| * The algorithm steps are formally described as follows: |
| * |
| * <pre> |
| * CTR Encryption: O[j] = E(K)(T[j]); for j = 1, 2...n; |
| * C[j] = P[j] ˆ O[j]; for j = 1, 2...n. |
| * CTR Decryption: O[j] = E(K)(T[j]); for j = 1, 2...n; |
| * P[j] = C[j] ˆ O[j]; for j = 1, 2...n. |
| * </pre> |
| * |
| * <p> |
| * where <code>P</code> is the plaintext, <code>C</code> is the ciphertext, |
| * <code>E(K)</code> is the underlying block cipher encryption function |
| * parametrised with the session key <code>K</code>, and <code>T</code> is |
| * the <i>Counter</i>. |
| * <p> |
| * This implementation, uses a standard incrementing function with a step of 1, |
| * and an initial value similar to that described in the NIST document. |
| * <p> |
| * References: |
| * <ol> |
| * <li><a |
| * href="http://csrc.nist.gov/encryption/modes/Recommendation/Modes01.pdf"> |
| * Recommendation for Block Cipher Modes of Operation Methods and Techniques</a>, |
| * Morris Dworkin.</li> |
| * </ol> |
| */ |
| public class CTR |
| extends BaseMode |
| implements Cloneable |
| { |
| private int off; |
| private byte[] counter, enc; |
| |
| /** |
| * Trivial package-private constructor for use by the Factory class. |
| * |
| * @param underlyingCipher the underlying cipher implementation. |
| * @param cipherBlockSize the underlying cipher block size to use. |
| */ |
| CTR(IBlockCipher underlyingCipher, int cipherBlockSize) |
| { |
| super(Registry.CTR_MODE, underlyingCipher, cipherBlockSize); |
| } |
| |
| /** |
| * Private constructor for cloning purposes. |
| * |
| * @param that the instance to clone. |
| */ |
| private CTR(CTR that) |
| { |
| this((IBlockCipher) that.cipher.clone(), that.cipherBlockSize); |
| } |
| |
| public Object clone() |
| { |
| return new CTR(this); |
| } |
| |
| public void setup() |
| { |
| if (modeBlockSize > cipherBlockSize) |
| throw new IllegalArgumentException("mode size exceeds cipher block size"); |
| off = 0; |
| counter = new byte[cipherBlockSize]; |
| int i = cipherBlockSize - 1; |
| int j = iv.length - 1; |
| while (i >= 0 && j >= 0) |
| counter[i--] = iv[j--]; |
| enc = new byte[cipherBlockSize]; |
| cipher.encryptBlock(counter, 0, enc, 0); |
| } |
| |
| public void teardown() |
| { |
| if (counter != null) |
| Arrays.fill(counter, (byte) 0); |
| if (enc != null) |
| Arrays.fill(enc, (byte) 0); |
| } |
| |
| public void encryptBlock(byte[] in, int i, byte[] out, int o) |
| { |
| ctr(in, i, out, o); |
| } |
| |
| public void decryptBlock(byte[] in, int i, byte[] out, int o) |
| { |
| ctr(in, i, out, o); |
| } |
| |
| public Iterator blockSizes() |
| { |
| return new Sequence(1, cipherBlockSize).iterator(); |
| } |
| |
| private void ctr(byte[] in, int inOffset, byte[] out, int outOffset) |
| { |
| for (int i = 0; i < modeBlockSize; i++) |
| { |
| out[outOffset++] = (byte)(in[inOffset++] ^ enc[off++]); |
| if (off == cipherBlockSize) |
| { |
| int j; |
| for (j = cipherBlockSize - 1; j >= 0; j--) |
| { |
| counter[j]++; |
| if ((counter[j] & 0xFF) != 0) |
| break; |
| } |
| if (j == 0) |
| counter[cipherBlockSize - 1]++; |
| off = 0; |
| cipher.encryptBlock(counter, 0, enc, 0); |
| } |
| } |
| } |
| } |