using System;

/*
 * $Id: IVGenerator.cs,v 1.3 2006/12/25 00:38:15 psoares33 Exp $
 *
 * Copyright 2006 Paulo Soares
 *
 * The contents of this file are subject to the Mozilla Public License Version 1.1
 * (the "License"); you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at http://www.mozilla.org/MPL/
 *
 * Software distributed under the License is distributed on an "AS IS" basis,
 * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
 * for the specific language governing rights and limitations under the License.
 *
 * The Original Code is 'iText, a free JAVA-PDF library'.
 *
 * The Initial Developer of the Original Code is Bruno Lowagie. Portions created by
 * the Initial Developer are Copyright (C) 1999, 2000, 2001, 2002 by Bruno Lowagie.
 * All Rights Reserved.
 * Co-Developer of the code is Paulo Soares. Portions created by the Co-Developer
 * are Copyright (C) 2000, 2001, 2002 by Paulo Soares. All Rights Reserved.
 *
 * Contributor(s): all the names of the contributors are added in the source code
 * where applicable.
 *
 * Alternatively, the contents of this file may be used under the terms of the
 * LGPL license (the "GNU LIBRARY GENERAL PUBLIC LICENSE"), in which case the
 * provisions of LGPL are applicable instead of those above.  If you wish to
 * allow use of your version of this file only under the terms of the LGPL
 * License and not to allow others to use your version of this file under
 * the MPL, indicate your decision by deleting the provisions above and
 * replace them with the notice and other provisions required by the LGPL.
 * If you do not delete the provisions above, a recipient may use your version
 * of this file under either the MPL or the GNU LIBRARY GENERAL PUBLIC LICENSE.
 *
 * This library is free software; you can redistribute it and/or modify it
 * under the terms of the MPL as stated above or under the terms of the GNU
 * Library General Public License as published by the Free Software Foundation;
 * either version 2 of the License, or any later version.
 *
 * This library 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 Library general Public License for more
 * details.
 *
 * If you didn't download this code from the following link, you should check if
 * you aren't using an obsolete version:
 * http://www.lowagie.com/iText/
 */
namespace iTextSharp.text.pdf.crypto {

/**
 * An initialization vector generator for a CBC block encryption. It's a random generator based on RC4.
 * @author Paulo Soares (psoares@consiste.pt)
 */
    public class IVGenerator {
        
        private static RC4Encryption rc4;
        
        static IVGenerator(){
            rc4 = new RC4Encryption();
            byte[] longBytes = new byte[8];
            long val = DateTime.Now.Ticks;
            for (int i = 0; i != 8; i++) {
                longBytes[i] = (byte)val;
                val = (long)((ulong)val >> 8);
            }
            rc4.PrepareRC4Key(longBytes);
        }
        
        /** Creates a new instance of IVGenerator */
        private IVGenerator() {
        }
        
    /**
     * Gets a 16 byte random initialization vector.
     * @return a 16 byte random initialization vector
     */
        public static byte[] GetIV() {
            return GetIV(16);
        }

        /**
        * Gets a random initialization vector.
        * @param len the length of the initialization vector
        * @return a random initialization vector
        */
        public static byte[] GetIV(int len) {
            byte[] b = new byte[len];
            lock (rc4) {
                rc4.EncryptRC4(b);
            }
            return b;
        }    
    }
}