rc4.java

来自「jpeg2000编解码」· Java 代码 · 共 456 行 · 第 1/2 页

//............................................................................

    /**
     * Will hold the contents of the current set S-box.
     */
    private int[] sBox = new int[256];

    /**
     * The two indices for the S-box computation referred to as i and j
     * in Schneier.
     */
    private int x, y;

    /**
     * The block size of this cipher. Being a stream cipher this value
     * is 1!
     */
    private static final int BLOCK_SIZE = 1;


// Constructor, finalizer, and clone()
//............................................................................

    /**
     * Constructs an RC4 cipher object, in the UNINITIALIZED state.
     * This calls the Cipher constructor with <i>implBuffering</i> false,
     * <i>implPadding</i> false and the provider set to "Cryptix".
     */
    public RC4() {
        super(false, false, "Cryptix");
    }

    /**
     * Cleans up resources used by this instance, if necessary.
     */
    protected final void finalize() {
        if (native_lock != null) {
            synchronized(native_lock) {
                String error = native_finalize(); // may be called more than once
                if (error != null)
                    debug(error + " in native_finalize");
            }
        }
    }

    /**
     * Always throws a CloneNotSupportedException (cloning of ciphers is not
     * supported for security reasons).
     */
    public final Object clone() throws CloneNotSupportedException {
        throw new CloneNotSupportedException();
    }


// Implementation of JCE methods
//............................................................................
    
    /**
     * <b>SPI</b>: Returns the length of an input block, in bytes.
     *
     * @return the length in bytes of an input block for this cipher.
     */
    public int engineBlockSize () { return BLOCK_SIZE; }

    /**
     * <b>SPI</b>: Initializes this cipher for encryption, using the
     * specified key.
     *
     * @param  key  the key to use for encryption.
     * @exception InvalidKeyException if the key is invalid.
     */
    public void engineInitEncrypt(Key key)
    throws InvalidKeyException {
        makeKey(key);
    }

    /**
     * <b>SPI</b>: Initializes this cipher for decryption, using the
     * specified key.
     *
     * @param  key  the key to use for decryption.
     * @exception InvalidKeyException if the key is invalid.
     */
    public void engineInitDecrypt(Key key)
    throws InvalidKeyException {
        makeKey(key);
    }

    /**
     * <b>SPI</b>: This is the main engine method for updating data.
     * <p>
     * <i>in</i> and <i>out</i> may be the same array, and the input and output
     * regions may overlap.
     *
     * @param  in           the input data.
     * @param  inOffset     the offset into in 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 out array.
     * @return the number of bytes written.
     * @exception CryptixException if the native library is being used, and it
     *                      reports an error.
     */
    protected int
    engineUpdate(byte[] in, int inOffset, int inLen, byte[] out, int outOffset) {
        if (inLen < 0) throw new IllegalArgumentException("inLen < 0");

        boolean doEncrypt = (getState() == ENCRYPT);

        // Avoid overlapping input and output regions.
        if (in == out && (outOffset >= inOffset && outOffset < (long)inOffset+inLen ||
                          inOffset >= outOffset && inOffset < (long)outOffset+inLen)) {
            byte[] newin = new byte[inLen];
            System.arraycopy(in, inOffset, newin, 0, inLen);
            in = newin;
            inOffset = 0;
        }
        if (native_lock != null) {
            synchronized(native_lock) {
                // If in == null || out == 0, evaluating their lengths will throw a
                // NullPointerException.

                if (inOffset < 0 || (long)inOffset + inLen > in.length ||
                    outOffset < 0 || (long)outOffset + inLen > out.length)
                    throw new ArrayIndexOutOfBoundsException(getAlgorithm() +
                        ": Arguments to native_crypt would cause a buffer overflow");

                if (0 == native_crypt(native_cookie, in, inOffset, inLen, out, outOffset))
                    throw new CryptixException(getAlgorithm() + ": Error in native code");
            }
        } else
            rc4(in, inOffset, inLen, out, outOffset);

        return inLen;
    }


// Own methods
//............................................................................

    /**
     * RC4 encryption/decryption. The input and output regions are assumed not to
     * overlap.
     *
     * @param  in           the input data.
     * @param  inOffset     the offset into in 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 out array.
     */
    private void rc4(byte[] in, int inOffset, int inLen, byte[] out, int outOffset) {
        int xorIndex, t;

        for (int i = 0; i < inLen; i++) {
            x = (x + 1) & 0xFF;
            y = (sBox[x] + y) & 0xFF;

            t = sBox[x];
            sBox[x] = sBox[y];
            sBox[y] = t;

            xorIndex = (sBox[x] + sBox[y]) & 0xFF;
            out[outOffset++] = (byte)(in[inOffset++] ^ sBox[xorIndex]);
        }
    }

    /**
     * Expands a user-key to a working key schedule.
     * <p>
     * The key bytes are first extracted from the user-key and then
     * used to build the contents of this key schedule.
     * <p>
     * The method's only exceptions are when the user-key's contents
     * are null, or a byte array of zero length.
     *
     * @param  key  the user-key object to use.
     * @exception InvalidKeyException if one of the following occurs: <ul>
     *                <li> key.getEncoded() == null;
     *                <li> The encoded byte array form of the key is zero-length;
     *              </ul>
     */
    private void makeKey(Key key)
    throws InvalidKeyException {

        byte[] userkey = key.getEncoded();
        if (userkey == null)
            throw new InvalidKeyException(getAlgorithm() + ": Null user key");

        int len = userkey.length;
        if (len == 0)
            throw new InvalidKeyException(getAlgorithm() + ": Invalid user key length");

        // If native library available then use it. If not or if
        // native method returned error then revert to 100% Java.

        if (native_lock != null) {
            synchronized(native_lock) {
                try {
                    linkStatus.check(native_ks(native_cookie, userkey));
                    return;
                } catch (Error error) {
                    native_finalize();
                    native_lock = null;
if (DEBUG && debuglevel > 0) debug(error + ". Will use 100% Java.");
                }
            }
        }

        x =  y = 0;
        for (int i = 0; i < 256; i++)
            sBox[i] = i;

        int i1 = 0, i2 = 0, t;

        for (int i = 0; i < 256; i++) {
            i2 = ((userkey[i1] & 0xFF) + sBox[i] + i2) & 0xFF;

            t = sBox[i];
            sBox[i] = sBox[i2];
            sBox[i2] = t;

            i1 = (i1 + 1) % len;
        }
    }
}