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 }