001    /* MessageDigestSpi.java --- The message digest service provider interface.
002       Copyright (C) 1999, 2005  Free Software Foundation, Inc.
003    
004    This file is part of GNU Classpath.
005    
006    GNU Classpath is free software; you can redistribute it and/or modify
007    it under the terms of the GNU General Public License as published by
008    the Free Software Foundation; either version 2, or (at your option)
009    any later version.
010    
011    GNU Classpath is distributed in the hope that it will be useful, but
012    WITHOUT ANY WARRANTY; without even the implied warranty of
013    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
014    General Public License for more details.
015    
016    You should have received a copy of the GNU General Public License
017    along with GNU Classpath; see the file COPYING.  If not, write to the
018    Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
019    02110-1301 USA.
020    
021    Linking this library statically or dynamically with other modules is
022    making a combined work based on this library.  Thus, the terms and
023    conditions of the GNU General Public License cover the whole
024    combination.
025    
026    As a special exception, the copyright holders of this library give you
027    permission to link this library with independent modules to produce an
028    executable, regardless of the license terms of these independent
029    modules, and to copy and distribute the resulting executable under
030    terms of your choice, provided that you also meet, for each linked
031    independent module, the terms and conditions of the license of that
032    module.  An independent module is a module which is not derived from
033    or based on this library.  If you modify this library, you may extend
034    this exception to your version of the library, but you are not
035    obligated to do so.  If you do not wish to do so, delete this
036    exception statement from your version. */
037    
038    package java.security;
039    
040    import java.nio.ByteBuffer;
041    
042    /**
043       This is the Service Provider Interface (SPI) for MessageDigest
044       class in java.security. It provides the back end functionality
045       for the MessageDigest class so that it can compute message
046       hashes. The default hashes are SHA-1 and MD5. A message hash
047       takes data of arbitrary length and produces a unique number
048       representing it.
049    
050       Cryptography service providers who want to implement their
051       own message digest hashes need only to subclass this class.
052    
053       The implementation of a Cloneable interface is left to up to
054       the programmer of a subclass.
055    
056       @version 0.0
057    
058       @author Mark Benvenuto (ivymccough@worldnet.att.net)
059     */
060    public abstract class MessageDigestSpi
061    {
062      /**
063         Default constructor of the MessageDigestSpi class
064       */
065      public MessageDigestSpi()
066      {
067      }
068    
069      /**
070         Returns the length of the digest.  It may be overridden by the
071         provider to return the length of the digest.  Default is to
072         return 0.  It is concrete for backwards compatibility with JDK1.1
073         message digest classes.
074    
075         @return Length of Digest in Bytes
076    
077         @since 1.2
078       */
079      protected int engineGetDigestLength()
080      {
081        return 0;
082      }
083    
084      /**
085         Updates the digest with the specified byte.
086    
087         @param input the byte to update digest with
088       */
089      protected abstract void engineUpdate(byte input);
090    
091    
092      /**
093         Updates the digest with the specified bytes starting with the
094         offset and proceeding for the specified length.
095    
096         @param input the byte array to update digest with
097         @param offset the offset of the byte to start with
098         @param len the number of the bytes to update with
099       */
100      protected abstract void engineUpdate(byte[]input, int offset, int len);
101    
102      /**
103       * Updates this digest with the remaining bytes of a byte buffer.
104       * 
105       * @param input The input buffer.
106       * @since 1.5
107       */
108      protected void engineUpdate (ByteBuffer input)
109      {
110        byte[] buf = new byte[1024];
111        while (input.hasRemaining())
112          {
113            int n = Math.min(input.remaining(), buf.length);
114            input.get (buf, 0, n);
115            engineUpdate (buf, 0, n);
116          }
117      }
118      
119      /**
120         Computes the final digest of the stored bytes and returns
121         them. It performs any necessary padding. The message digest
122         should reset sensitive data after performing the digest.
123    
124         @return An array of bytes containing the digest
125       */
126      protected abstract byte[] engineDigest();
127    
128      /**
129         Computes the final digest of the stored bytes and returns
130         them. It performs any necessary padding. The message digest
131         should reset sensitive data after performing the digest.  This
132         method is left concrete for backwards compatibility with JDK1.1
133         message digest classes.
134    
135         @param buf An array of bytes to store the digest
136         @param offset An offset to start storing the digest at
137         @param len The length of the buffer
138         @return Returns the length of the buffer
139    
140         @since 1.2
141       */
142      protected int engineDigest(byte[]buf, int offset, int len)
143        throws DigestException
144      {
145        if (engineGetDigestLength() > len)
146          throw new DigestException("Buffer is too small.");
147    
148        byte[] tmp = engineDigest();
149        if (tmp.length > len)
150          throw new DigestException("Buffer is too small");
151    
152        System.arraycopy(tmp, 0, buf, offset, tmp.length);
153        return tmp.length;
154      }
155    
156      /**
157         Resets the digest engine. Reinitializes internal variables
158         and clears sensitive data.
159       */
160      protected abstract void engineReset();
161    
162      /**
163         Returns a clone of this class.
164    
165         If cloning is not supported, then by default the class throws a
166         CloneNotSupportedException.  The MessageDigestSpi provider
167         implementation has to overload this class in order to be
168         cloneable.
169       */
170      public Object clone() throws CloneNotSupportedException
171      {
172        return super.clone();
173      }
174    }