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+/* 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.Configuration;
+import gnu.java.security.Registry;
+import gnu.java.security.util.Util;
+
+import java.util.logging.Logger;
+
+/**
+ * The implementation of the Trailing Bit Complement (TBC) padding algorithm.
+ * <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:
+ * <ol>
+ * <li><a
+ * href="http://csrc.nist.gov/encryption/modes/Recommendation/Modes01.pdf">
+ * Recommendation for Block Cipher Modes of Operation Methods and
+ * Techniques</a>, Morris Dworkin.</li>
+ * </ol>
+ */
+public final class TBC
+    extends BasePad
+{
+  private static final Logger log = Logger.getLogger(TBC.class.getName());
+
+  /**
+   * Trivial package-private constructor for use by the <i>Factory</i> class.
+   *
+   * @see PadFactory
+   */
+  TBC()
+  {
+    super(Registry.TBC_PAD);
+  }
+
+  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 (Configuration.DEBUG)
+      log.fine("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 (Configuration.DEBUG)
+      log.fine("padding length: " + result);
+    return result;
+  }
+}