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+/* MessageDigestSpi.java --- The message digest service provider interface.
+   Copyright (C) 1999, 2005  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;
+
+/**
+   This is the Service Provider Interface (SPI) for MessageDigest
+   class in java.security. It provides the back end functionality
+   for the MessageDigest class so that it can compute message
+   hashes. The default hashes are SHA-1 and MD5. A message hash
+   takes data of arbitrary length and produces a unique number
+   representing it.
+
+   Cryptography service providers who want to implement their
+   own message digest hashes need only to subclass this class.
+
+   The implementation of a Cloneable interface is left to up to
+   the programmer of a subclass.
+
+   @version 0.0
+
+   @author Mark Benvenuto (ivymccough@worldnet.att.net)
+ */
+public abstract class MessageDigestSpi
+{
+  /**
+     Default constructor of the MessageDigestSpi class
+   */
+  public MessageDigestSpi()
+  {
+  }
+
+  /**
+     Returns the length of the digest.  It may be overridden by the
+     provider to return the length of the digest.  Default is to
+     return 0.  It is concrete for backwards compatibility with JDK1.1
+     message digest classes.
+
+     @return Length of Digest in Bytes
+
+     @since 1.2
+   */
+  protected int engineGetDigestLength()
+  {
+    return 0;
+  }
+
+  /**
+     Updates the digest with the specified byte.
+
+     @param input the byte to update digest with
+   */
+  protected abstract void engineUpdate(byte input);
+
+
+  /**
+     Updates the digest with the specified bytes starting with the
+     offset and proceeding for the specified length.
+
+     @param input the byte array to update digest with
+     @param offset the offset of the byte to start with
+     @param len the number of the bytes to update with
+   */
+  protected abstract void engineUpdate(byte[]input, int offset, int len);
+
+  /**
+     Computes the final digest of the stored bytes and returns
+     them. It performs any necessary padding. The message digest
+     should reset sensitive data after performing the digest.
+
+     @return An array of bytes containing the digest
+   */
+  protected abstract byte[] engineDigest();
+
+  /**
+     Computes the final digest of the stored bytes and returns
+     them. It performs any necessary padding. The message digest
+     should reset sensitive data after performing the digest.  This
+     method is left concrete for backwards compatibility with JDK1.1
+     message digest classes.
+
+     @param buf An array of bytes to store the digest
+     @param offset An offset to start storing the digest at
+     @param len The length of the buffer
+     @return Returns the length of the buffer
+
+     @since 1.2
+   */
+  protected int engineDigest(byte[]buf, int offset, int len)
+    throws DigestException
+  {
+    if (engineGetDigestLength() > len)
+      throw new DigestException("Buffer is too small.");
+
+    byte[] tmp = engineDigest();
+    if (tmp.length > len)
+      throw new DigestException("Buffer is too small");
+
+    System.arraycopy(tmp, 0, buf, offset, tmp.length);
+    return tmp.length;
+  }
+
+  /**
+     Resets the digest engine. Reinitializes internal variables
+     and clears sensitive data.
+   */
+  protected abstract void engineReset();
+
+  /**
+     Returns a clone of this class.
+
+     If cloning is not supported, then by default the class throws a
+     CloneNotSupportedException.  The MessageDigestSpi provider
+     implementation has to overload this class in order to be
+     cloneable.
+   */
+  public Object clone() throws CloneNotSupportedException
+  {
+    return super.clone();
+  }
+}