/* TripleDES.java -- 
   Copyright (C) 2002, 2006 Free Software Foundation, Inc.

This file is a part of GNU Classpath.

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it under the terms of the GNU General Public License as published by
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Linking this library statically or dynamically with other modules is
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package gnu.javax.crypto.cipher;

import gnu.java.security.Registry;

import java.util.ArrayList;
import java.util.Collections;
import java.util.Iterator;
import java.security.InvalidKeyException;

/**
 * Triple-DES, 3DES, or DESede is a <i>combined cipher</i> that uses three
 * iterations of the Data Encryption Standard cipher to theoretically improve
 * the security of plain DES, at the cost of speed.
 * <p>
 * Triple-DES runs the DES algorithm three times with one, two or three
 * independent 56-bit (DES) keys. When used with one DES key, the cipher behaves
 * exactly like a (slower) DES.
 * <p>
 * To encrypt:
 * <blockquote><i>C<sub>i</sub> = E<sub>k3</sub> ( E<sub>k2</sub><sup>-1</sup> (
 * E<sub>k1</sub> ( P<sub>i</sub> )))</i>
 * </blockquote>
 * <p>
 * And to decrypt:
 * <blockquote><i>P<sub>i</sub> = E<sub>k1</sub><sup>-1</sup> (
 * E<sub>k2</sub> ( E<sub>k3</sub><sup>-1</sup> ( C<sub>i</sub> )))</i>
 * </blockquote>
 * <p>
 * (The "ede" comes from the encryption operation, which runs
 * Encrypt-Decrypt-Encrypt)
 * <p>
 * References:
 * <ol>
 * <li>Bruce Schneier, <i>Applied Cryptography: Protocols, Algorithms, and
 * Source Code in C, Second Edition</i>. (1996 John Wiley and Sons) ISBN
 * 0-471-11709-9. Page 294--295.</li>
 * </ol>
 */
public class TripleDES
    extends BaseCipher
{
  /** Triple-DES only operates on 64 bit blocks. */
  public static final int BLOCK_SIZE = 8;
  /** By default, Triple-DES uses 168 bits of a parity-adjusted 192 bit key. */
  public static final int KEY_SIZE = 24;
  /** The underlying DES instance. */
  private DES des;

  /**
   * Default 0-arguments constructor.
   */
  public TripleDES()
  {
    super(Registry.TRIPLEDES_CIPHER, BLOCK_SIZE, KEY_SIZE);
    des = new DES();
  }

  /**
   * Convenience method which calls the method with same name and three
   * arguments, passing <code>3</code> as the value of the first parameter.
   * 
   * @param kb The key bytes to adjust.
   * @param offset The starting offset into the key bytes.
   */
  public static void adjustParity(byte[] kb, int offset)
  {
    adjustParity(3, kb, offset);
  }

  /**
   * Adjusts, in-situ, the parity of the designated bytes, so they can be used
   * as DES keys for a 3-DES 1-, 2- or 3-key cipher.
   * 
   * @param keyCount the number of independent DES keys. Can be either
   *          <code>1</code>, <code>2</code> or <code>3</code>. Any other value
   *          will cause an {@link IllegalArgumentException} to be raised.
   * @param kb the array containing the key bytes to adjust. MUST have at least
   *          <code>8 * keyCount</code> bytes starting at offset position
   *          <code>offset</code>, otherwise an
   *          {@link ArrayIndexOutOfBoundsException} will be raised.
   * @param offset the starting offset into the array.
   * @see DES#adjustParity(byte[],int)
   */
  public static void adjustParity(int keyCount, byte[] kb, int offset)
  {
    if (keyCount < 1 || keyCount > 3)
      throw new IllegalArgumentException("Invalid keyCount value: " + keyCount);
    DES.adjustParity(kb, offset);
    if (keyCount > 1)
      DES.adjustParity(kb, offset + 8);
    if (keyCount > 2)
      DES.adjustParity(kb, offset + 16);
  }

  /**
   * Convenience method which calls the method with same name and three
   * arguments, passing <code>3</code> as the value of the first parameter.
   * 
   * @param kb The key bytes to test.
   * @param offset The starting offset into the key bytes.
   * @return <code>true</code> if the bytes in <i>kb</i> starting at
   *         <i>offset</i> are parity adjusted.
   * @see DES#isParityAdjusted(byte[],int)
   * @see #adjustParity(byte[],int)
   */
  public static boolean isParityAdjusted(byte[] kb, int offset)
  {
    return isParityAdjusted(3, kb, offset);
  }

  /**
   * Tests if enough bytes, expected to be used as DES keys for a 3-DES 1-, 2-
   * or 3-key cipher, located in a designated byte array, has already been
   * parity adjusted.
   * 
   * @param keyCount the number of independent DES keys. Can be either
   *          <code>1</code>, <code>2</code> or <code>3</code>. Any other value
   *          will cause an {@link IllegalArgumentException} to be raised.
   * @param kb the array containing the key bytes to test. MUST have at least
   *          <code>8 * keyCount</code> bytes starting at offset position
   *          <code>offset</code>, otherwise an
   *          {@link ArrayIndexOutOfBoundsException} will be raised.
   * @param offset the starting offset into the array.
   * @return <code>true</code> if the bytes in <i>kb</i> starting at
   *         <i>offset</i> are parity adjusted.
   * @see DES#isParityAdjusted(byte[],int)
   * @see #adjustParity(int,byte[],int)
   */
  public static boolean isParityAdjusted(int keyCount, byte[] kb, int offset)
  {
    if (keyCount < 1 || keyCount > 3)
      throw new IllegalArgumentException("Invalid keyCount value: " + keyCount);
    boolean result = DES.isParityAdjusted(kb, offset);
    if (keyCount > 1)
      result = result && DES.isParityAdjusted(kb, offset + 8);
    if (keyCount > 2)
      result = result && DES.isParityAdjusted(kb, offset + 16);
    return result;
  }

  public Object clone()
  {
    return new TripleDES();
  }

  public Iterator blockSizes()
  {
    return Collections.singleton(Integer.valueOf(BLOCK_SIZE)).iterator();
  }

  public Iterator keySizes()
  {
    ArrayList al = new ArrayList();
    al.add(Integer.valueOf(8));
    al.add(Integer.valueOf(16));
    al.add(Integer.valueOf(24));
    return Collections.unmodifiableList(al).iterator();
  }

  public Object makeKey(byte[] kb, int bs) throws InvalidKeyException
  {
    if (kb.length != 8 && kb.length != 16 && kb.length != 24)
      throw new InvalidKeyException("TripleDES key must be 8, 16 or 24 bytes: "
                                    + kb.length);
    Context ctx = new Context();
    byte[] k1 = new byte[DES.KEY_SIZE];
    System.arraycopy(kb, 0, k1, 0, DES.KEY_SIZE);
    if (! DES.isParityAdjusted(k1, 0))
      DES.adjustParity(k1, 0);
    ctx.k1 = (DES.Context) des.makeKey(k1, bs);

    if (kb.length == 8)
      {
        ctx.k2 = (DES.Context) des.makeKey(k1, bs);
        ctx.k3 = (DES.Context) des.makeKey(k1, bs);
      }
    else
      {
        byte[] k2 = new byte[DES.KEY_SIZE];
        System.arraycopy(kb, DES.KEY_SIZE, k2, 0, DES.KEY_SIZE);
        if (! DES.isParityAdjusted(k2, 0))
          DES.adjustParity(k2, 0);
        ctx.k2 = (DES.Context) des.makeKey(k2, bs);

        byte[] k3 = new byte[DES.KEY_SIZE];
        if (kb.length == 16)
          ctx.k3 = (DES.Context) des.makeKey(k1, bs);
        else
          {
            System.arraycopy(kb, 2 * DES.KEY_SIZE, k3, 0, DES.KEY_SIZE);
            if (! DES.isParityAdjusted(k3, 0))
              DES.adjustParity(k3, 0);
            ctx.k3 = (DES.Context) des.makeKey(k3, bs);
          }
      }
    return ctx;
  }

  public void encrypt(byte[] in, int i, byte[] out, int o, Object K, int bs)
  {
    byte[] temp = new byte[BLOCK_SIZE];
    des.encrypt(in, i, temp, 0, ((Context) K).k1, bs);
    des.decrypt(temp, 0, temp, 0, ((Context) K).k2, bs);
    des.encrypt(temp, 0, out, o, ((Context) K).k3, bs);
  }

  public void decrypt(byte[] in, int i, byte[] out, int o, Object K, int bs)
  {
    byte[] temp = new byte[BLOCK_SIZE];
    des.decrypt(in, i, temp, 0, ((Context) K).k3, bs);
    des.encrypt(temp, 0, temp, 0, ((Context) K).k2, bs);
    des.decrypt(temp, 0, out, o, ((Context) K).k1, bs);
  }

  private final class Context
  {
    DES.Context k1, k2, k3;
  }
}