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DSSSignatureRawCodec.java

package gnu.crypto.sig.dss;

// ----------------------------------------------------------------------------
// $Id: DSSSignatureRawCodec.java,v 1.5 2005/10/06 04:24:18 rsdio Exp $
//
// Copyright (C) 2001, 2002, 2003 Free Software Foundation, Inc.
//
// This file is part of GNU Crypto.
//
// GNU Crypto 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, or (at your option)
// any later version.
//
// GNU Crypto 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 this program; see the file COPYING.  If not, write to the
//
//    Free Software Foundation Inc.,
//    51 Franklin Street, 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.
// ----------------------------------------------------------------------------

import gnu.crypto.Registry;
import gnu.crypto.sig.ISignatureCodec;

import java.io.ByteArrayOutputStream;
import java.math.BigInteger;

/**
 * <p>An object that implements the {@link ISignatureCodec} operations for the
 * <i>Raw</i> format to use with DSS signatures.</p>
 *
 * @version $Revision: 1.5 $
 */
00058 public class DSSSignatureRawCodec implements ISignatureCodec {

   // Constants and variables
   // -------------------------------------------------------------------------

   // Constructor(s)
   // -------------------------------------------------------------------------

   // implicit 0-arguments constructor

   // Class methods
   // -------------------------------------------------------------------------

   // Instance methods
   // -------------------------------------------------------------------------

   // gnu.crypto.sig.ISignatureCodec interface implementation -----------------

   public int getFormatID() {
      return RAW_FORMAT;
   }

   /**
    * <p>Returns the encoded form of the designated DSS (Digital Signature
    * Standard) signature object according to the <i>Raw</i> format supported by
    * this library.</p>
    *
    * <p>The <i>Raw</i> format for a DSA signature, in this implementation, is a
    * byte sequence consisting of the following:</p>
    *
    * <ol>
    *       <li>4-byte magic consisting of the value of the literal
    *    {@link Registry#MAGIC_RAW_DSS_SIGNATURE},</li>
    *       <li>1-byte version consisting of the constant: 0x01,</li>
    *       <li>4-byte count of following bytes representing the DSS parameter
    *       <code>r</code> in internet order,</li>
    *       <li>n-bytes representation of a {@link BigInteger} obtained by invoking
    *    the <code>toByteArray()</code> method on the DSS parameter <code>r</code>,</li>
    *       <li>4-byte count of following bytes representing the DSS parameter
    *       <code>s</code>,</li>
    *       <li>n-bytes representation of a {@link BigInteger} obtained by invoking
    *    the <code>toByteArray()</code> method on the DSS parameter <code>s</code>.</li>
    * </ol>
    *
    * @param signature the signature to encode, consisting of the two DSS
    * parameters <code>r</code> and <code>s</code> as a {@link java.math.BigInteger}
    * array.
    * @return the <i>Raw</i> format encoding of the designated signature.
    * @exception IllegalArgumentException if the designated signature is not a
    * DSS (Digital Signature Standard) one.
    */
00109    public byte[] encodeSignature(Object signature) {
      BigInteger r, s;
      try {
         BigInteger[] sig = (BigInteger[]) signature;
         r = sig[0];
         s = sig[1];
      } catch (Exception x) {
         throw new IllegalArgumentException("key");
      }

      ByteArrayOutputStream baos = new ByteArrayOutputStream();

      // magic
      baos.write(Registry.MAGIC_RAW_DSS_SIGNATURE[0]);
      baos.write(Registry.MAGIC_RAW_DSS_SIGNATURE[1]);
      baos.write(Registry.MAGIC_RAW_DSS_SIGNATURE[2]);
      baos.write(Registry.MAGIC_RAW_DSS_SIGNATURE[3]);

      // version
      baos.write(0x01);

      // r
      byte[] buffer = r.toByteArray();
      int length = buffer.length;
      baos.write( length >>> 24        );
      baos.write((length >>> 16) & 0xFF);
      baos.write((length >>>  8) & 0xFF);
      baos.write( length         & 0xFF);
      baos.write(buffer, 0, length);

      // s
      buffer = s.toByteArray();
      length = buffer.length;
      baos.write( length >>> 24        );
      baos.write((length >>> 16) & 0xFF);
      baos.write((length >>>  8) & 0xFF);
      baos.write( length         & 0xFF);
      baos.write(buffer, 0, length);

      return baos.toByteArray();
   }

   public Object decodeSignature(byte[] k) {
      // magic
      if (k[0] != Registry.MAGIC_RAW_DSS_SIGNATURE[0]
            || k[1] != Registry.MAGIC_RAW_DSS_SIGNATURE[1]
            || k[2] != Registry.MAGIC_RAW_DSS_SIGNATURE[2]
            || k[3] != Registry.MAGIC_RAW_DSS_SIGNATURE[3]) {
         throw new IllegalArgumentException("magic");
      }

      // version
      if (k[4] != 0x01) {
         throw new IllegalArgumentException("version");
      }

      int i = 5;
      int l;
      byte[] buffer;

      // r
      l = k[i++] << 24 | (k[i++] & 0xFF) << 16 | (k[i++] & 0xFF) << 8 | (k[i++] & 0xFF);
      buffer = new byte[l];
      System.arraycopy(k, i, buffer, 0, l);
      i += l;
      BigInteger r = new BigInteger(1, buffer);

      // s
      l = k[i++] << 24 | (k[i++] & 0xFF) << 16 | (k[i++] & 0xFF) << 8 | (k[i++] & 0xFF);
      buffer = new byte[l];
      System.arraycopy(k, i, buffer, 0, l);
      i += l;
      BigInteger s = new BigInteger(1, buffer);

      return new BigInteger[] {r, s};
   }
}

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