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Diffstat (limited to 'libjava/classpath/gnu/javax/crypto/pad/TBC.java')
| -rw-r--r-- | libjava/classpath/gnu/javax/crypto/pad/TBC.java | 156 |
1 files changed, 156 insertions, 0 deletions
diff --git a/libjava/classpath/gnu/javax/crypto/pad/TBC.java b/libjava/classpath/gnu/javax/crypto/pad/TBC.java new file mode 100644 index 00000000000..25c3e4286bc --- /dev/null +++ b/libjava/classpath/gnu/javax/crypto/pad/TBC.java @@ -0,0 +1,156 @@ +/* TBC.java -- + Copyright (C) 2001, 2002, 2006 Free Software Foundation, Inc. + +This file is a part of GNU Classpath. + +GNU Classpath is free software; you can redistribute it and/or modify +it under the terms of the GNU General Public License as published by +the Free Software Foundation; either version 2 of the License, or (at +your option) any later version. + +GNU Classpath is distributed in the hope that it will be useful, but +WITHOUT ANY WARRANTY; without even the implied warranty of +MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU +General Public License for more details. + +You should have received a copy of the GNU General Public License +along with GNU Classpath; if not, write to the Free Software +Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 +USA + +Linking this library statically or dynamically with other modules is +making a combined work based on this library. Thus, the terms and +conditions of the GNU General Public License cover the whole +combination. + +As a special exception, the copyright holders of this library give you +permission to link this library with independent modules to produce an +executable, regardless of the license terms of these independent +modules, and to copy and distribute the resulting executable under +terms of your choice, provided that you also meet, for each linked +independent module, the terms and conditions of the license of that +module. An independent module is a module which is not derived from +or based on this library. If you modify this library, you may extend +this exception to your version of the library, but you are not +obligated to do so. If you do not wish to do so, delete this +exception statement from your version. */ + + +package gnu.javax.crypto.pad; + +import gnu.java.security.Registry; +import gnu.java.security.util.Util; + +import java.io.PrintWriter; + +/** + * <p>The implementation of the Trailing Bit Complement (TBC) padding algorithm.</p> + * + * <p>In this mode, "...the data string is padded at the trailing end with the + * complement of the trailing bit of the unpadded message: if the trailing bit + * is <tt>1</tt>, then <tt>0</tt> bits are appended, and if the trailing bit is + * <tt>0</tt>, then <tt>1</tt> bits are appended. As few bits are added as are + * necessary to meet the formatting size requirement."</p> + * + * References:<br> + * <a href="http://csrc.nist.gov/encryption/modes/Recommendation/Modes01.pdf"> + * Recommendation for Block Cipher Modes of Operation Methods and Techniques</a>, + * Morris Dworkin.<p> + */ +public final class TBC extends BasePad +{ + + // Debugging methods and variables + // ------------------------------------------------------------------------- + + private static final String NAME = "tbc"; + + private static final boolean DEBUG = false; + + private static final int debuglevel = 9; + + private static final PrintWriter err = new PrintWriter(System.out, true); + + private static void debug(String s) + { + err.println(">>> " + NAME + ": " + s); + } + + // Constants and variables + // ------------------------------------------------------------------------- + + // Constructor(s) + // ------------------------------------------------------------------------- + + /** + * Trivial package-private constructor for use by the <i>Factory</i> class.<p> + * + * @see gnu.crypto.pad.PadFactory + */ + TBC() + { + super(Registry.TBC_PAD); + } + + // Class methods + // ------------------------------------------------------------------------- + + // Implementation of abstract methods in BasePad + // ------------------------------------------------------------------------- + + public void setup() + { + if (blockSize < 1 || blockSize > 256) + { + throw new IllegalArgumentException(); + } + } + + public byte[] pad(byte[] in, int offset, int length) + { + int padLength = blockSize; + if (length % blockSize != 0) + { + padLength = blockSize - length % blockSize; + } + byte[] result = new byte[padLength]; + int lastBit = in[offset + length - 1] & 0x01; + if (lastBit == 0) + { + for (int i = 0; i < padLength;) + { + result[i++] = 0x01; + } + } // else it's already set to zeroes by virtue of initialisation + + if (DEBUG && debuglevel > 8) + { + debug("padding: 0x" + Util.toString(result)); + } + return result; + } + + public int unpad(byte[] in, int offset, int length) + throws WrongPaddingException + { + int limit = offset + length - 1; + int lastBit = in[limit] & 0xFF; + int result = 0; + while (lastBit == (in[limit] & 0xFF)) + { + result++; + limit--; + } + + if (result > length) + { + throw new WrongPaddingException(); + } + + if (DEBUG && debuglevel > 8) + { + debug("padding length: " + String.valueOf(result)); + } + return result; + } +}
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