mirror of git://gcc.gnu.org/git/gcc.git
120 lines
3.9 KiB
Java
120 lines
3.9 KiB
Java
/* TBC.java --
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Copyright (C) 2001, 2002, 2006, 2010 Free Software Foundation, Inc.
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This file is a part of GNU Classpath.
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GNU Classpath is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2 of the License, or (at
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your option) any later version.
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GNU Classpath is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with GNU Classpath; if not, write to the Free Software
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Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301
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USA
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Linking this library statically or dynamically with other modules is
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making a combined work based on this library. Thus, the terms and
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conditions of the GNU General Public License cover the whole
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combination.
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As a special exception, the copyright holders of this library give you
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permission to link this library with independent modules to produce an
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executable, regardless of the license terms of these independent
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modules, and to copy and distribute the resulting executable under
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terms of your choice, provided that you also meet, for each linked
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independent module, the terms and conditions of the license of that
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module. An independent module is a module which is not derived from
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or based on this library. If you modify this library, you may extend
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this exception to your version of the library, but you are not
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obligated to do so. If you do not wish to do so, delete this
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exception statement from your version. */
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package gnu.javax.crypto.pad;
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import gnu.java.security.Configuration;
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import gnu.java.security.Registry;
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import gnu.java.security.util.Util;
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import java.util.logging.Logger;
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/**
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* The implementation of the Trailing Bit Complement (TBC) padding algorithm.
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* <p>
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* In this mode, "...the data string is padded at the trailing end with the
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* complement of the trailing bit of the unpadded message: if the trailing bit
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* is <tt>1</tt>, then <tt>0</tt> bits are appended, and if the trailing
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* bit is <tt>0</tt>, then <tt>1</tt> bits are appended. As few bits are
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* added as are necessary to meet the formatting size requirement."
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* <p>
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* References:
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* <ol>
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* <li><a
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* href="http://csrc.nist.gov/encryption/modes/Recommendation/Modes01.pdf">
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* Recommendation for Block Cipher Modes of Operation Methods and
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* Techniques</a>, Morris Dworkin.</li>
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* </ol>
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*/
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public final class TBC
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extends BasePad
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{
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private static final Logger log = Configuration.DEBUG ?
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Logger.getLogger(TBC.class.getName()) : null;
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/**
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* Trivial package-private constructor for use by the <i>Factory</i> class.
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*
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* @see PadFactory
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*/
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TBC()
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{
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super(Registry.TBC_PAD);
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}
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public void setup()
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{
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if (blockSize < 1 || blockSize > 256)
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throw new IllegalArgumentException();
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}
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public byte[] pad(byte[] in, int offset, int length)
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{
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int padLength = blockSize;
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if (length % blockSize != 0)
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padLength = blockSize - length % blockSize;
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byte[] result = new byte[padLength];
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int lastBit = in[offset + length - 1] & 0x01;
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if (lastBit == 0)
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for (int i = 0; i < padLength;)
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result[i++] = 0x01;
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// else it's already set to zeroes by virtue of initialisation
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if (Configuration.DEBUG)
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log.fine("padding: 0x" + Util.toString(result));
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return result;
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}
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public int unpad(byte[] in, int offset, int length)
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throws WrongPaddingException
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{
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int limit = offset + length - 1;
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int lastBit = in[limit] & 0xFF;
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int result = 0;
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while (lastBit == (in[limit] & 0xFF))
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{
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result++;
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limit--;
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}
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if (result > length)
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throw new WrongPaddingException();
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if (Configuration.DEBUG)
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log.fine("padding length: " + result);
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return result;
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}
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}
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