// $Id: OFB.java,v 1.5 1997/11/21 05:45:11 hopwood Exp $//// $Log: OFB.java,v $// Revision 1.5  1997/11/21 05:45:11  hopwood// + Missed a name change.//// Revision 1.4  1997/11/20 19:39:32  hopwood// + cryptix.util.* name changes.//// Revision 1.3.1  1997/11/16  David Hopwood// + Removed commented-out code (since we will be using FeedbackMode//   permanently now).// + Fixed imports.// + Added check that IV is set in engineUpdate.// + Removed reset(byte[] iv) method.// + Removed (ivStart == null) case in cryptByte, since we now require//   the IV to always be set.//// Revision 1.3  1997/11/07 05:53:25  raif// *** empty log message ***//// Revision 1.2  1997/11/05 08:01:56  raif// + Added initialisation of currentByte in engineInitEncrypt/Decrypt//   to force proper handling of the iv in successive uses of the Mode//   instance object without the need to re-setInitializationVector().// + Call cipher.update instead of cipher.crypt.// + Added Aug/97 fixes.//// Revision 1.1.1.1  1997/11/03 22:36:56  hopwood// + Imported to CVS (tagged as 'start').//// $Endlog$/* * Copyright (c) 1995-1997 Systemics Ltd * on behalf of the Cryptix Development Team.  All rights reserved. */package cryptix.provider.mode;import cryptix.CryptixException;import java.security.Cipher;import java.security.Key;import java.security.KeyException;import java.security.InvalidParameterException;import java.security.IllegalBlockSizeException;/** * Implements a byte-oriented stream cipher using n-bit OFB with an * n-bit-sized block cipher. * <p> * The full block size of the supplied cipher is used for the * Output Feedback Mode. The bytes supplied are processed and * returned immediately. * <p> * <b>References:</b> * <ol> *   <li> <a href="mailto:schneier@counterpane.com">Bruce Schneier</a>, *        "Section 9.8 Output Feedback Mode," and "Section 9.11 Choosing a Cipher Mode," *        <cite>Applied Cryptography, 2nd edition</cite>, *        John Wiley &amp; Sons, 1996 *        <p> *   <li> <code>sci.crypt</code> FAQ, "Part 5: Product Ciphers," *        <a href="ftp://ftp.rtfm.mit.edu/pub/usenet/news.answers/cryptography-faq/part05"> *        ftp://ftp.rtfm.mit.edu/pub/usenet/news.answers/cryptography-faq/part05</a> *        <p> *   <li> National Bureau of Standards (now NIST), *        "DES Modes of Operation," *        <cite>NBS FIPS PUB 81</cite>, *        U.S. Department of Commerce, December 1980 * </ol> * <p> * <b>Copyright</b> &copy; 1997 * <a href="http://www.systemics.com/">Systemics Ltd</a> on behalf of the * <a href="http://www.systemics.com/docs/cryptix/">Cryptix Development Team</a>. * <br>All rights reserved. * <p> * <b>$Revision: 1.5 $</b> * @author David Hopwood * @author Raif S. Naffah * @since  Cryptix 2.2.2 */public class OFBextends FeedbackMode{// Constructors//...........................................................................    /**     * Constructs an OFB cipher, assuming that the IV will be provided     * via <code>setInitializationVector</code>.     * <p>     * The IV value must be unique during the lifetime of the key.     * <strong>If it is not unique, and an attacker has access to a different     * message encrypted under the same IV and key, all of the plaintext can     * normally be recovered.</strong>     */    public OFB() {        super(true, false, "Cryptix");  // implements its own buffering    }    /**     * Constructs an OFB cipher, assuming that the IV will be provided     * via <code>setInitializationVector</code>.     * See the previous constructor for more details.     *     * @param  cipher   the cipher object to use in OFB mode.     * @exception NullPointerException if cipher == null     * @exception IllegalBlockSizeException if cipher.getPlaintextBlockSize() !=     *                  cipher.getCiphertextBlockSize()     */    public OFB(Cipher cipher) {        this();        engineSetCipher(cipher);    }    /**     * Constructs a OFB cipher, using an initialization vector     * provided in the constructor.     * <p>     * The IV value must be unique during the lifetime of the key.     * <strong>If it is not unique, and an attacker has access to a different     * message encrypted under the same IV and key, all of the plaintext can     * normally be recovered.</strong>     *     * @param  cipher   the block cipher to use     * @param  iv       the initial value for the shift register (IV)     * @exception NullPointerException if cipher == null     */    public OFB(Cipher cipher, byte[] iv) {        this(cipher);        setInitializationVector(iv);    }// FeedbackMode and Mode methods//...........................................................................// Implementations from FeedbackMode are sufficient.// Cipher methods//...........................................................................    protected int engineBlockSize() { return 1; }    protected void engineInitEncrypt(Key newkey)    throws KeyException {        cipher.initEncrypt(newkey);        if (ivStart != null) System.arraycopy(ivStart, 0, ivBlock, 0, length);        currentByte = length;               // to force crypting the iv    }    protected void engineInitDecrypt(Key newkey)    throws KeyException {        cipher.initEncrypt(newkey);        if (ivStart != null) System.arraycopy(ivStart, 0, ivBlock, 0, length);        currentByte = length;               // to force crypting the iv    }    /**     * <b>SPI</b>: This is the main engine method for updating data.     * It may be called with any size of input.     * <p>     * <code>in</code> and <code>out</code> may be the same array, and the     * input and output regions may overlap.     *     * @param in        the input data.     * @param inOffset  the offset into <code>in</code> specifying where     *                  the data starts.     * @param inLen     the length of the subarray.     * @param out       the output array.     * @param outOffset the offset indicating where to start writing into     *                  the <code>out</code> array.     * @return the number of bytes written.     */    protected int engineUpdate(byte[] in, int inOffset, int inLen, byte[] out,                                int outOffset) {        if (ivBlock == null)            throw new InvalidParameterException("OFB: IV is not set");        if (getState() == UNINITIALIZED)            throw new CryptixException("OFB: Cipher not initialized");        if (in == out && outOffset > inOffset &&            outOffset < (long)inOffset+inLen) {            // The input array would be overwritten, so copy it.            byte[] newin = new byte[inLen];            System.arraycopy(in, inOffset, newin, 0, inLen);            in = newin;            inOffset = 0;        }        for (int i = 0; i < inLen; i++)            out[i + outOffset] = cryptByte(in[i + inOffset]);        return inLen;    }// Own methods//...........................................................................    /**     * Encrypts or decrypts a byte in OFB mode (encryption and decryption     * use the same algorithm).     */    private byte cryptByte(byte b) {        if (currentByte >= length) {            currentByte = 0;//            cipher.crypt(ivBlock, 0, length, ivBlock, 0);            cipher.update(ivBlock, 0, length, ivBlock, 0);        }        b ^= ivBlock[currentByte];        currentByte++;        return b;    }}