001/* MessageDigestSpi.java --- The message digest service provider interface.
002   Copyright (C) 1999, 2005  Free Software Foundation, Inc.
003
004This file is part of GNU Classpath.
005
006GNU Classpath is free software; you can redistribute it and/or modify
007it under the terms of the GNU General Public License as published by
008the Free Software Foundation; either version 2, or (at your option)
009any later version.
010
011GNU Classpath is distributed in the hope that it will be useful, but
012WITHOUT ANY WARRANTY; without even the implied warranty of
013MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
014General Public License for more details.
015
016You should have received a copy of the GNU General Public License
017along with GNU Classpath; see the file COPYING.  If not, write to the
018Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
01902110-1301 USA.
020
021Linking this library statically or dynamically with other modules is
022making a combined work based on this library.  Thus, the terms and
023conditions of the GNU General Public License cover the whole
024combination.
025
026As a special exception, the copyright holders of this library give you
027permission to link this library with independent modules to produce an
028executable, regardless of the license terms of these independent
029modules, and to copy and distribute the resulting executable under
030terms of your choice, provided that you also meet, for each linked
031independent module, the terms and conditions of the license of that
032module.  An independent module is a module which is not derived from
033or based on this library.  If you modify this library, you may extend
034this exception to your version of the library, but you are not
035obligated to do so.  If you do not wish to do so, delete this
036exception statement from your version. */
037
038package java.security;
039
040import 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 */
060public 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}