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+/* 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
+the Free Software Foundation; either version 2, or (at your option)
+any later version.
+
+GNU Classpath is distributed in the hope that it will be useful, but
+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; see the file COPYING.  If not, write to the
+Free Software Foundation, Inc., 51 Franklin Street, 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
+module.  An independent module is a module which is not derived from
+or based on this library.  If you modify this library, you may extend
+this exception to your version of the library, but you are not
+obligated to do so.  If you do not wish to do so, delete this
+exception statement from your version. */
+
+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();
+  }
+}