/* MessageDigest.java --- The message digest interface.
   Copyright (C) 1999, 2002, 2003 Free Software Foundation, Inc.

This file is 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
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permission to link this library with independent modules to produce an
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package java.security;

import gnu.java.security.Engine;

/**
 * <p>This <code>MessageDigest</code> class provides applications the
 * functionality of a message digest algorithm, such as <i>MD5</i> or <i>SHA</i>.
 * Message digests are secure one-way hash functions that take arbitrary-sized
 * data and output a fixed-length hash value.</p>
 *
 * <p>A <code>MessageDigest</code> object starts out initialized. The data is
 * processed through it using the <code>update()</code> methods. At any point
 * <code>reset()</code> can be called to reset the digest. Once all the data to
 * be updated has been updated, one of the <code>digest()</code> methods should
 * be called to complete the hash computation.</p>
 *
 * <p>The <code>digest()</code> method can be called <b>once</b> for a given
 * number of updates. After <code>digest()</code> has been called, the
 * <code>MessageDigest</code> object is <b>reset</b> to its initialized state.
 * </p>
 *
 * <p>Implementations are free to implement the {@link Cloneable} interface.
 * Client applications can test cloneability by attempting cloning and catching
 * the {@link CloneNotSupportedException}:
 *
 * <pre>
 *    MessageDigest md = MessageDigest.getInstance("SHA");
 *    try
 *      {
 *        md.update(toChapter1);
 *        MessageDigest tc1 = md.clone();
 *        byte[] toChapter1Digest = tc1.digest();
 *        md.update(toChapter2);
 *        // ...
 *      }
 *    catch (CloneNotSupportedException x)
 *      {
 *        throw new DigestException("couldn't make digest of partial content");
 *      }
 * </pre>
 *
 * <p>Note that if a given implementation is not cloneable, it is still possible
 * to compute intermediate digests by instantiating several instances, if the
 * number of digests is known in advance.</p>
 *
 * <p>Note that this class is abstract and extends from {@link MessageDigestSpi}
 * for historical reasons. Application developers should only take notice of the
 * methods defined in this <code>MessageDigest</code> class; all the methods in
 * the superclass are intended for cryptographic service providers who wish to
 * supply their own implementations of message digest algorithms.</p>
 *
 * @see MessageDigestSpi
 * @see Provider
 * @since JDK 1.1
 */
public abstract class MessageDigest extends MessageDigestSpi
{
  /** The service name for message digests. */
  private static final String MESSAGE_DIGEST = "MessageDigest";

  private String algorithm;
  Provider provider;
  private byte[] lastDigest;

  /**
   * Creates a message digest with the specified algorithm name.
   *
   * @param algorithm the standard name of the digest algorithm.
   * See Appendix A in the Java Cryptography Architecture API
   * Specification &amp; Reference for information about standard
   * algorithm names.
   */
  protected MessageDigest(String algorithm)
  {
    this.algorithm = algorithm;
    provider = null;
  }

  /**
   * Generates a <code>MessageDigest</code> object that implements the specified
   * digest algorithm. If the default provider package provides an
   * implementation of the requested digest algorithm, an instance of
   * <code>MessageDigest</code> containing that implementation is returned. If
   * the algorithm is not available in the default package, other packages are
   * searched.
   *
   * @param algorithm the name of the algorithm requested. See Appendix A in the
   * Java Cryptography Architecture API Specification &amp; Reference for
   * information about standard algorithm names.
   * @return a Message Digest object implementing the specified algorithm.
   * @throws NoSuchAlgorithmException if the algorithm is not available in the
   * caller's environment.
   */
  public static MessageDigest getInstance(String algorithm)
    throws NoSuchAlgorithmException
  {
    Provider[] p = Security.getProviders();
    for (int i = 0; i < p.length; i++)
      {
        try
          {
            return getInstance(algorithm, p[i]);
          }
        catch (NoSuchAlgorithmException ignored)
	  {
	    // Ignore.
	  }
      }

    throw new NoSuchAlgorithmException(algorithm);
  }

  /**
   * Generates a <code>MessageDigest</code> object implementing the specified
   * algorithm, as supplied from the specified provider, if such an algorithm is
   * available from the provider.
   *
   * @param algorithm the name of the algorithm requested. See Appendix A in the
   * Java Cryptography Architecture API Specification &amp; Reference for
   * information about standard algorithm names.
   * @param provider the name of the provider.
   * @return a Message Digest object implementing the specified algorithm.
   * @throws NoSuchAlgorithmException if the algorithm is not available in the
   * package supplied by the requested provider.
   * @throws NoSuchProviderException if the provider is not available in the
   * environment.
   * @throws IllegalArgumentException if the provider name is null or empty.
   * @see Provider
   */
  public static MessageDigest getInstance(String algorithm, String provider)
    throws NoSuchAlgorithmException, NoSuchProviderException
  {
    if (provider == null || provider.length() == 0)
      throw new IllegalArgumentException("Illegal provider");

    Provider p = Security.getProvider(provider);
    if (p == null)
      throw new NoSuchProviderException(provider);

    return getInstance(algorithm, p);
  }

  /**
   * Generates a <code>MessageDigest</code> object implementing the specified
   * algorithm, as supplied from the specified provider, if such an algorithm
   * is available from the provider. Note: the provider doesn't have to be
   * registered.
   *
   * @param algorithm the name of the algorithm requested. See Appendix A in
   * the Java Cryptography Architecture API Specification &amp; Reference for
   * information about standard algorithm names.
   * @param provider the provider.
   * @return a Message Digest object implementing the specified algorithm.
   * @throws NoSuchAlgorithmException if the <code>algorithm</code> is not
   * available in the package supplied by the requested <code>provider</code>.
   * @throws IllegalArgumentException if the <code>provider</code> is
   * <code>null</code>.
   * @since 1.4
   * @see Provider
   */
  public static MessageDigest getInstance(String algorithm, Provider provider)
    throws NoSuchAlgorithmException
  {
    if (provider == null)
      throw new IllegalArgumentException("Illegal provider");

    MessageDigest result = null;
    Object o = null;
    try
      {
        o = Engine.getInstance(MESSAGE_DIGEST, algorithm, provider);
      }
    catch (java.lang.reflect.InvocationTargetException ite)
      {
        throw new NoSuchAlgorithmException(algorithm);
      }

    if (o instanceof MessageDigestSpi)
      {
        result = new DummyMessageDigest((MessageDigestSpi) o, algorithm);
      }
    else if (o instanceof MessageDigest)
      {
        result = (MessageDigest) o;
        result.algorithm = algorithm;
      }
    else
      {
        throw new NoSuchAlgorithmException(algorithm);
      }
    result.provider = provider;
    return result;
  }

  /**
   * Returns the provider of this message digest object.
   *
   * @return the provider of this message digest object.
   */
  public final Provider getProvider()
  {
    return provider;
  }

  /**
   * Updates the digest using the specified byte.
   *
   * @param input the byte with which to update the digest.
   */
  public void update(byte input)
  {
    engineUpdate(input);
  }

  /**
   * Updates the digest using the specified array of bytes, starting at the
   * specified offset.
   *
   * @param input the array of bytes.
   * @param offset the offset to start from in the array of bytes.
   * @param len the number of bytes to use, starting at offset.
   */
  public void update(byte[] input, int offset, int len)
  {
    engineUpdate(input, offset, len);
  }

  /**
   * Updates the digest using the specified array of bytes.
   *
   * @param input the array of bytes.
   */
  public void update(byte[] input)
  {
    engineUpdate(input, 0, input.length);
  }

  /**
   * Completes the hash computation by performing final operations such as
   * padding. The digest is reset after this call is made.
   *
   * @return the array of bytes for the resulting hash value.
   */
  public byte[] digest()
  {
    return lastDigest = engineDigest();
  }

  /**
   * Completes the hash computation by performing final operations such as
   * padding. The digest is reset after this call is made.
   *
   * @param buf An output buffer for the computed digest.
   * @param offset The offset into the output buffer to begin storing the digest.
   * @param len The number of bytes within buf allotted for the digest.
   * @return The number of bytes placed into buf.
   * @throws DigestException if an error occurs.
   */
  public int digest(byte[] buf, int offset, int len) throws DigestException
  {
    return engineDigest(buf, offset, len);
  }

  /**
   * Performs a final update on the digest using the specified array of bytes,
   * then completes the digest computation. That is, this method first calls
   * <code>update(input)</code>, passing the input array to the <code>update()
   * </code> method, then calls <code>digest()</code>.
   *
   * @param input the input to be updated before the digest is completed.
   * @return the array of bytes for the resulting hash value.
   */
  public byte[] digest(byte[] input)
  {
    update(input);
    return digest();
  }

  /**
   * Returns a string representation of this message digest object.
   *
   * @return a string representation of the object.
   */
  public String toString()
  {
    return (getClass()).getName() + " Message Digest <" + digestToString() + ">";
  }

  /**
   * Compares two digests for equality. Does a simple byte compare.
   *
   * @param digesta one of the digests to compare.
   * @param digestb the other digest to compare.
   * @return <code>true</code> if the digests are equal, <code>false</code>
   * otherwise.
   */
  public static boolean isEqual(byte[] digesta, byte[] digestb)
  {
    if (digesta.length != digestb.length)
      return false;

    for (int i = digesta.length - 1; i >= 0; --i)
      if (digesta[i] != digestb[i])
        return false;

    return true;
  }

  /** Resets the digest for further use. */
  public void reset()
  {
    engineReset();
  }

  /**
   * Returns a string that identifies the algorithm, independent of
   * implementation details. The name should be a standard Java Security name
   * (such as <code>"SHA"</code>, <code>"MD5"</code>, and so on). See Appendix
   * A in the Java Cryptography Architecture API Specification &amp; Reference
   * for information about standard algorithm names.
   *
   * @return the name of the algorithm.
   */
  public final String getAlgorithm()
  {
    return algorithm;
  }

  /**
   * Returns the length of the digest in bytes, or <code>0</code> if this
   * operation is not supported by the provider and the implementation is not
   * cloneable.
   *
   * @return the digest length in bytes, or <code>0</code> if this operation is
   * not supported by the provider and the implementation is not cloneable.
   * @since 1.2
   */
  public final int getDigestLength()
  {
    return engineGetDigestLength();
  }

  /**
   * Returns a clone if the implementation is cloneable.
   *
   * @return a clone if the implementation is cloneable.
   * @throws CloneNotSupportedException if this is called on an implementation
   * that does not support {@link Cloneable}.
   */
  public Object clone() throws CloneNotSupportedException
  {
    return super.clone();
  }

  private String digestToString()
  {
    byte[] digest = lastDigest;

    if (digest == null)
      return "incomplete";

    StringBuffer buf = new StringBuffer();
    int len = digest.length;
    for (int i = 0; i < len; ++i)
      {
        byte b = digest[i];
        byte high = (byte) ((b & 0xff) >>> 4);
        byte low = (byte) (b & 0xf);

        buf.append(high > 9 ? ('a' - 10) + high : '0' + high);
        buf.append(low > 9 ? ('a' - 10) + low : '0' + low);
      }

    return buf.toString();
  }
}