libjava/java/security/MessageDigestSpi.java

   1 /* MessageDigestSpi.java --- The message digest service provider interface.
   2    Copyright (C) 1999, 2005  Free Software Foundation, Inc.
   3
   4 This file is part of GNU Classpath.
   5
   6 GNU Classpath is free software; you can redistribute it and/or modify
   7 it under the terms of the GNU General Public License as published by
   8 the Free Software Foundation; either version 2, or (at your option)
   9 any later version.
  10
  11 GNU Classpath is distributed in the hope that it will be useful, but
  12 WITHOUT ANY WARRANTY; without even the implied warranty of
  13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14 General Public License for more details.
  15
  16 You should have received a copy of the GNU General Public License
  17 along with GNU Classpath; see the file COPYING.  If not, write to the
  18 Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  19 02111-1307 USA.
  20
  21 Linking this library statically or dynamically with other modules is
  22 making a combined work based on this library.  Thus, the terms and
  23 conditions of the GNU General Public License cover the whole
  24 combination.
  25
  26 As a special exception, the copyright holders of this library give you
  27 permission to link this library with independent modules to produce an
  28 executable, regardless of the license terms of these independent
  29 modules, and to copy and distribute the resulting executable under
  30 terms of your choice, provided that you also meet, for each linked
  31 independent module, the terms and conditions of the license of that
  32 module.  An independent module is a module which is not derived from
  33 or based on this library.  If you modify this library, you may extend
  34 this exception to your version of the library, but you are not
  35 obligated to do so.  If you do not wish to do so, delete this
  36 exception statement from your version. */
  37
  38 package java.security;
  39
  40 /**
  41    This is the Service Provider Interface (SPI) for MessageDigest
  42    class in java.security. It provides the back end functionality
  43    for the MessageDigest class so that it can compute message
  44    hashes. The default hashes are SHA-1 and MD5. A message hash
  45    takes data of arbitrary length and produces a unique number
  46    representing it.
  47
  48    Cryptography service providers who want to implement their
  49    own message digest hashes need only to subclass this class.
  50
  51    The implementation of a Cloneable interface is left to up to
  52    the programmer of a subclass.
  53
  54    @version 0.0
  55
  56    @author Mark Benvenuto (ivymccough@worldnet.att.net)
  57  */
  58 public abstract class MessageDigestSpi
  59 {
  60   /**
  61      Default constructor of the MessageDigestSpi class
  62    */
  63   public MessageDigestSpi()
  64   {
  65   }
  66
  67   /**
  68      Returns the length of the digest.  It may be overridden by the
  69      provider to return the length of the digest.  Default is to
  70      return 0.  It is concrete for backwards compatibility with JDK1.1
  71      message digest classes.
  72
  73      @return Length of Digest in Bytes
  74
  75      @since 1.2
  76    */
  77   protected int engineGetDigestLength()
  78   {
  79     return 0;
  80   }
  81
  82   /**
  83      Updates the digest with the specified byte.
  84
  85      @param input the byte to update digest with
  86    */
  87   protected abstract void engineUpdate(byte input);
  88
  89
  90   /**
  91      Updates the digest with the specified bytes starting with the
  92      offset and proceeding for the specified length.
  93
  94      @param input the byte array to update digest with
  95      @param offset the offset of the byte to start with
  96      @param len the number of the bytes to update with
  97    */
  98   protected abstract void engineUpdate(byte[]input, int offset, int len);
  99
 100   /**
 101      Computes the final digest of the stored bytes and returns
 102      them. It performs any necessary padding. The message digest
 103      should reset sensitive data after performing the digest.
 104
 105      @return An array of bytes containing the digest
 106    */
 107   protected abstract byte[] engineDigest();
 108
 109   /**
 110      Computes the final digest of the stored bytes and returns
 111      them. It performs any necessary padding. The message digest
 112      should reset sensitive data after performing the digest.  This
 113      method is left concrete for backwards compatibility with JDK1.1
 114      message digest classes.
 115
 116      @param buf An array of bytes to store the digest
 117      @param offset An offset to start storing the digest at
 118      @param len The length of the buffer
 119      @return Returns the length of the buffer
 120
 121      @since 1.2
 122    */
 123   protected int engineDigest(byte[]buf, int offset, int len)
 124     throws DigestException
 125   {
 126     if (engineGetDigestLength() > len)
 127       throw new DigestException("Buffer is too small.");
 128
 129     byte[] tmp = engineDigest();
 130     if (tmp.length > len)
 131       throw new DigestException("Buffer is too small");
 132
 133     System.arraycopy(tmp, 0, buf, offset, tmp.length);
 134     return tmp.length;
 135   }
 136
 137   /**
 138      Resets the digest engine. Reinitializes internal variables
 139      and clears sensitive data.
 140    */
 141   protected abstract void engineReset();
 142
 143   /**
 144      Returns a clone of this class.
 145
 146      If cloning is not supported, then by default the class throws a
 147      CloneNotSupportedException.  The MessageDigestSpi provider
 148      implementation has to overload this class in order to be
 149      cloneable.
 150    */
 151   public Object clone() throws CloneNotSupportedException
 152   {
 153     return super.clone();
 154   }
 155 }