/* MD2.java -- 
   Copyright (C) 2001, 2002, 2006 Free Software Foundation, Inc.

This file is a part of GNU Classpath.

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Linking this library statically or dynamically with other modules is
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package gnu.java.security.hash;

import gnu.java.security.Registry;
import gnu.java.security.util.Util;

/**
 * <p>An implementation of the MD2 message digest algorithm.</p>
 *
 * <p>MD2 is not widely used. Unless it is needed for compatibility with
 * existing systems, it is not recommended for use in new applications.</p>
 *
 * <p>References:</p>
 *
 * <ol>
 *    <li>The <a href="http://www.ietf.org/rfc/rfc1319.txt">MD2</a>
 *    Message-Digest Algorithm.<br>
 *    B. Kaliski.</li>
 *    <li>The <a href="http://www.rfc-editor.org/errata.html">RFC ERRATA PAGE</a>
 *    under section RFC 1319.</li>
 * </ol>
 */
public class MD2 extends BaseHash
{

  // Constants and variables
  // -------------------------------------------------------------------------

  /** An MD2 message digest is always 128-bits long, or 16 bytes. */
  private static final int DIGEST_LENGTH = 16;

  /** The MD2 algorithm operates on 128-bit blocks, or 16 bytes. */
  private static final int BLOCK_LENGTH = 16;

  /** 256 byte "random" permutation of the digits of pi. */
  private static final byte[] PI = { 41, 46, 67, -55, -94, -40, 124, 1, 61, 54,
                                    84, -95, -20, -16, 6, 19, 98, -89, 5, -13,
                                    -64, -57, 115, -116, -104, -109, 43, -39,
                                    -68, 76, -126, -54, 30, -101, 87, 60, -3,
                                    -44, -32, 22, 103, 66, 111, 24, -118, 23,
                                    -27, 18, -66, 78, -60, -42, -38, -98, -34,
                                    73, -96, -5, -11, -114, -69, 47, -18, 122,
                                    -87, 104, 121, -111, 21, -78, 7, 63, -108,
                                    -62, 16, -119, 11, 34, 95, 33, -128, 127,
                                    93, -102, 90, -112, 50, 39, 53, 62, -52,
                                    -25, -65, -9, -105, 3, -1, 25, 48, -77, 72,
                                    -91, -75, -47, -41, 94, -110, 42, -84, 86,
                                    -86, -58, 79, -72, 56, -46, -106, -92, 125,
                                    -74, 118, -4, 107, -30, -100, 116, 4, -15,
                                    69, -99, 112, 89, 100, 113, -121, 32, -122,
                                    91, -49, 101, -26, 45, -88, 2, 27, 96, 37,
                                    -83, -82, -80, -71, -10, 28, 70, 97, 105,
                                    52, 64, 126, 15, 85, 71, -93, 35, -35, 81,
                                    -81, 58, -61, 92, -7, -50, -70, -59, -22,
                                    38, 44, 83, 13, 110, -123, 40, -124, 9,
                                    -45, -33, -51, -12, 65, -127, 77, 82, 106,
                                    -36, 55, -56, 108, -63, -85, -6, 36, -31,
                                    123, 8, 12, -67, -79, 74, 120, -120, -107,
                                    -117, -29, 99, -24, 109, -23, -53, -43, -2,
                                    59, 0, 29, 57, -14, -17, -73, 14, 102, 88,
                                    -48, -28, -90, 119, 114, -8, -21, 117, 75,
                                    10, 49, 68, 80, -76, -113, -19, 31, 26,
                                    -37, -103, -115, 51, -97, 17, -125, 20 };

  /** The output of this message digest when no data has been input. */
  private static final String DIGEST0 = "8350E5A3E24C153DF2275C9F80692773";

  /** caches the result of the correctness test, once executed. */
  private static Boolean valid;

  /** The checksum computed so far. */
  private byte[] checksum;

  /**
   * Work array needed by encrypt method. First <code>BLOCK_LENGTH</code> bytes
   * are also used to store the running digest.
   */
  private byte[] work;

  // Constructor(s)
  // -------------------------------------------------------------------------

  /** Creates a new MD2 digest ready for use. */
  public MD2()
  {
    super(Registry.MD2_HASH, DIGEST_LENGTH, BLOCK_LENGTH);
  }

  /**
   * <p>Private constructor used for cloning.</p>
   *
   * @param md2 the instance to clone.
   */
  private MD2(MD2 md2)
  {
    this();

    // superclass field
    this.count = md2.count;
    this.buffer = (byte[]) md2.buffer.clone();

    // private field
    this.checksum = (byte[]) md2.checksum.clone();
    this.work = (byte[]) md2.work.clone();
  }

  // Class methods
  // -------------------------------------------------------------------------

  // Instance methods
  // -------------------------------------------------------------------------

  // java.lang.Cloneable interface implementation ----------------------------

  public Object clone()
  {
    return new MD2(this);
  }

  // Implementation of abstract methods in BaseHash --------------------------

  protected byte[] getResult()
  {
    byte[] result = new byte[DIGEST_LENGTH];

    // Encrypt checksum as last block.
    encryptBlock(checksum, 0);

    for (int i = 0; i < BLOCK_LENGTH; i++)
      {
        result[i] = work[i];
      }

    return result;
  }

  protected void resetContext()
  {
    checksum = new byte[BLOCK_LENGTH];
    work = new byte[BLOCK_LENGTH * 3];
  }

  public boolean selfTest()
  {
    if (valid == null)
      {
        valid = Boolean.valueOf(DIGEST0.equals(Util.toString(new MD2().digest())));
      }
    return valid.booleanValue();
  }

  /**
   * <p>Generates an array of padding bytes. The padding is defined as
   * <code>i</code> bytes of value <code>i</code>, where <code>i</code> is the
   * number of bytes to fill the last block of the message to
   * <code>BLOCK_LENGTH</code> bytes (or <code>BLOCK_LENGTH</code> bytes when
   * the last block was completely full).</p>
   *
   * @return the bytes to pad the remaining bytes in the buffer before
   * completing a hash operation.
   */
  protected byte[] padBuffer()
  {
    int length = BLOCK_LENGTH - (int) (count % BLOCK_LENGTH);
    if (length == 0)
      {
        length = BLOCK_LENGTH;
      }
    byte[] pad = new byte[length];
    for (int i = 0; i < length; i++)
      {
        pad[i] = (byte) length;
      }
    return pad;
  }

  /**
   * <p>Adds <code>BLOCK_LENGTH</code> bytes to the running digest.</p>
   *
   * @param in the byte array to take the <code>BLOCK_LENGTH</code> bytes from.
   * @param off the offset to start from in the given byte array.
   */
  protected void transform(byte[] in, int off)
  {
    // encryptBlock(in, off);
    // updateCheckSum(in, off);
    updateCheckSumAndEncryptBlock(in, off);
  }

  // Private instance methods ------------------------------------------------

  /**
   * Updates the checksum with the <code>BLOCK_LENGTH</code> bytes from the
   * given array starting at <code>off</code>.
   */
  /*
   private void updateCheckSum(byte[] in, int off) {
   byte l = checksum[BLOCK_LENGTH-1];
   for (int i = 0; i < BLOCK_LENGTH; i++) {
   byte b = in[off+i];
   //         l = (byte)((checksum[i] & 0xFF) ^ (PI[((b & 0xFF) ^ (l & 0xFF))] & 0xFF));
   l = (byte)(checksum[i] ^ PI[(b ^ l) & 0xFF]);
   checksum[i] = l;
   }
   }
   */
  /**
   * Adds a new block (<code>BLOCK_LENGTH</code> bytes) to the running digest
   * from the given byte array starting from the given offset.
   */
  private void encryptBlock(byte[] in, int off)
  {
    for (int i = 0; i < BLOCK_LENGTH; i++)
      {
        byte b = in[off + i];
        work[BLOCK_LENGTH + i] = b;
        work[BLOCK_LENGTH * 2 + i] = (byte) (work[i] ^ b);
      }

    byte t = 0;
    for (int i = 0; i < 18; i++)
      {
        for (int j = 0; j < 3 * BLOCK_LENGTH; j++)
          {
            //            t = (byte)((work[j] & 0xFF) ^ (PI[t & 0xFF] & 0xFF));
            t = (byte) (work[j] ^ PI[t & 0xFF]);
            work[j] = t;
          }
        //         t = (byte)((t + i) & 0xFF);
        t = (byte) (t + i);
      }
  }

  /**
   * Optimized method that combines a checksum update and encrypt of a block.
   */
  private void updateCheckSumAndEncryptBlock(byte[] in, int off)
  {
    byte l = checksum[BLOCK_LENGTH - 1];
    for (int i = 0; i < BLOCK_LENGTH; i++)
      {
        byte b = in[off + i];
        work[BLOCK_LENGTH + i] = b;
        //         work[BLOCK_LENGTH*2+i] = (byte)((work[i] & 0xFF) ^ (b & 0xFF));
        work[BLOCK_LENGTH * 2 + i] = (byte) (work[i] ^ b);
        //         l = (byte)((checksum[i] & 0xFF) ^ (PI[((b & 0xFF) ^ (l & 0xFF))] & 0xFF));
        l = (byte) (checksum[i] ^ PI[(b ^ l) & 0xFF]);
        checksum[i] = l;
      }

    byte t = 0;
    for (int i = 0; i < 18; i++)
      {
        for (int j = 0; j < 3 * BLOCK_LENGTH; j++)
          {
            //            t = (byte)((work[j] & 0xFF) ^ (PI[t & 0xFF] & 0xFF));
            t = (byte) (work[j] ^ PI[t & 0xFF]);
            work[j] = t;
          }
        //         t = (byte)((t + i) & 0xFF);
        t = (byte) (t + i);
      }
  }
}