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Version modificada de iText 2.1.7 con el paquete cambiado, adaptaciones menores para firma y dependencias actualizadas.
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/*
 * $Id: IVGenerator.java 3242 2008-04-13 23:00:20Z xlv $
 *
 * 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/
 */
package com.aowagie.text.pdf.crypto;

/**
 * An initialization vector generator for a CBC block encryption. It's a random generator based on ARCFOUR.
 * @author Paulo Soares ([email protected])
 */
public final class IVGenerator {

    private static ARCFOUREncryption arcfour;

    static {
        arcfour = new ARCFOUREncryption();
        final long time = System.currentTimeMillis();
        final long mem = Runtime.getRuntime().freeMemory();
        final String s = time + "+" + mem;
        arcfour.prepareARCFOURKey(s.getBytes());
    }

    /** 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
     */
    private static byte[] getIV(final int len) {
        final byte[] b = new byte[len];
        synchronized (arcfour) {
            arcfour.encryptARCFOUR(b);
        }
        return b;
    }
}