/*
 * $Id: StandardDecryption.java,v 1.2 2006/11/09 18:20:12 xlv 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/
 */
package com.lowagie.text.pdf;

import com.lowagie.text.pdf.crypto.AESCipher;
import com.lowagie.text.pdf.crypto.RC4Encryption;

public class StandardDecryption {
    protected RC4Encryption rc4;
    protected AESCipher cipher;
    private byte[] key;
    private static final int AES_128 = 4;
    private boolean aes;
    private boolean initiated;
    private byte[] iv = new byte[16];
    private int ivptr;

    /** Creates a new instance of StandardDecryption */
    public StandardDecryption(byte key[], int off, int len, int revision) {
        aes = revision == AES_128;
        if (aes) {
            this.key = new byte[len];
            System.arraycopy(key, off, this.key, 0, len);
        }
        else {
            rc4 = new RC4Encryption();
            rc4.prepareRC4Key(key, off, len);
        }
    }
    
    public byte[] update(byte[] b, int off, int len) {
        if (aes) {
            if (initiated)
                return cipher.update(b, off, len);
            else {
                int left = Math.min(iv.length - ivptr, len);
                System.arraycopy(b, off, iv, ivptr, left);
                off += left;
                len -= left;
                ivptr += left;
                if (ivptr == iv.length) {
                    cipher = new AESCipher(false, key, iv);
                    initiated = true;
                    if (len > 0)
                        return cipher.update(b, off, len);
                }
                return null;
            }
        }
        else {
            byte[] b2 = new byte[len];
            rc4.encryptRC4(b, off, len, b2, 0);
            return b2;
        }
    }
    
    public byte[] finish() {
        if (aes) {
            return cipher.doFinal();
        }
        else
            return null;
    }
}