Source for java.security.MessageDigestSpi

   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., 51 Franklin Street, Fifth Floor, Boston, MA
  19: 02110-1301 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: }