package org.bouncycastle.crypto.engines;import org.bouncycastle.crypto.BlockCipher;import org.bouncycastle.crypto.CipherParameters;import org.bouncycastle.crypto.params.KeyParameter;import org.bouncycastle.crypto.params.RC5Parameters;/** * The specification for RC5 came from the <code>RC5 Encryption Algorithm</code> * publication in RSA CryptoBytes, Spring of 1995.  * <em>http://www.rsasecurity.com/rsalabs/cryptobytes</em>. * <p> * This implementation has a word size of 32 bits. * <p> * Implementation courtesy of Tito Pena. */public class RC532Engine    implements BlockCipher{    /*     * the number of rounds to perform     */    private int _noRounds;    /*     * the expanded key array of size 2*(rounds + 1)     */    private int _S[];    /*     * our "magic constants" for 32 32     *     * Pw = Odd((e-2) * 2^wordsize)     * Qw = Odd((o-2) * 2^wordsize)     *     * where e is the base of natural logarithms (2.718281828...)     * and o is the golden ratio (1.61803398...)     */    private static final int P32 = 0xb7e15163;    private static final int Q32 = 0x9e3779b9;    private boolean forEncryption;    /**     * Create an instance of the RC5 encryption algorithm     * and set some defaults     */    public RC532Engine()    {        _noRounds     = 12;         // the default        _S            = null;    }    public String getAlgorithmName()    {        return "RC5-32";    }    public int getBlockSize()    {        return 2 * 4;    }    /**     * initialise a RC5-32 cipher.     *     * @param forEncryption whether or not we are for encryption.     * @param params the parameters required to set up the cipher.     * @exception IllegalArgumentException if the params argument is     * inappropriate.     */    public void init(        boolean             forEncryption,        CipherParameters    params)    {        if (params instanceof RC5Parameters)        {            RC5Parameters       p = (RC5Parameters)params;            _noRounds     = p.getRounds();            setKey(p.getKey());        }        else if (params instanceof KeyParameter)        {            KeyParameter       p = (KeyParameter)params;            setKey(p.getKey());        }        else        {            throw new IllegalArgumentException("invalid parameter passed to RC532 init - " + params.getClass().getName());        }        this.forEncryption = forEncryption;    }    public int processBlock(        byte[]  in,        int     inOff,        byte[]  out,        int     outOff)    {        return (forEncryption) ? encryptBlock(in, inOff, out, outOff)                                     : decryptBlock(in, inOff, out, outOff);    }    public void reset()    {    }    /**     * Re-key the cipher.     * <p>     * @param  key  the key to be used     */    private void setKey(        byte[]      key)    {        //        // KEY EXPANSION:        //        // There are 3 phases to the key expansion.        //        // Phase 1:        //   Copy the secret key K[0...b-1] into an array L[0..c-1] of        //   c = ceil(b/u), where u = 32/8 in little-endian order.        //   In other words, we fill up L using u consecutive key bytes        //   of K. Any unfilled byte positions in L are zeroed. In the        //   case that b = c = 0, set c = 1 and L[0] = 0.        //        int[]   L = new int[(key.length + (4 - 1)) / 4];        for (int i = 0; i != key.length; i++)        {            L[i / 4] += (key[i] & 0xff) << (8 * (i % 4));        }        //        // Phase 2:        //   Initialize S to a particular fixed pseudo-random bit pattern        //   using an arithmetic progression modulo 2^wordsize determined        //   by the magic numbers, Pw & Qw.        //        _S            = new int[2*(_noRounds + 1)];        _S[0] = P32;        for (int i=1; i < _S.length; i++)        {            _S[i] = (_S[i-1] + Q32);        }        //        // Phase 3:        //   Mix in the user's secret key in 3 passes over the arrays S & L.        //   The max of the arrays sizes is used as the loop control        //        int iter;        if (L.length > _S.length)        {            iter = 3 * L.length;        }        else        {            iter = 3 * _S.length;        }        int A = 0, B = 0;        int i = 0, j = 0;        for (int k = 0; k < iter; k++)        {            A = _S[i] = rotateLeft(_S[i] + A + B, 3);            B =  L[j] = rotateLeft(L[j] + A + B, A+B);            i = (i+1) % _S.length;            j = (j+1) %  L.length;        }    }    /**     * Encrypt the given block starting at the given offset and place     * the result in the provided buffer starting at the given offset.     * <p>     * @param  in     in byte buffer containing data to encrypt     * @param  inOff  offset into src buffer     * @param  out     out buffer where encrypted data is written     * @param  outOff  offset into out buffer     */    private int encryptBlock(        byte[]  in,        int     inOff,        byte[]  out,        int     outOff)    {        int A = bytesToWord(in, inOff) + _S[0];        int B = bytesToWord(in, inOff + 4) + _S[1];        for (int i = 1; i <= _noRounds; i++)        {            A = rotateLeft(A ^ B, B) + _S[2*i];            B = rotateLeft(B ^ A, A) + _S[2*i+1];        }                wordToBytes(A, out, outOff);        wordToBytes(B, out, outOff + 4);                return 2 * 4;    }    private int decryptBlock(        byte[]  in,        int     inOff,        byte[]  out,        int     outOff)    {        int A = bytesToWord(in, inOff);        int B = bytesToWord(in, inOff + 4);        for (int i = _noRounds; i >= 1; i--)        {            B = rotateRight(B - _S[2*i+1], A) ^ A;            A = rotateRight(A - _S[2*i],   B) ^ B;        }                wordToBytes(A - _S[0], out, outOff);        wordToBytes(B - _S[1], out, outOff + 4);                return 2 * 4;    }        //////////////////////////////////////////////////////////////    //    // PRIVATE Helper Methods    //    //////////////////////////////////////////////////////////////    /**     * Perform a left "spin" of the word. The rotation of the given     * word <em>x</em> is rotated left by <em>y</em> bits.     * Only the <em>lg(32)</em> low-order bits of <em>y</em>     * are used to determine the rotation amount. Here it is      * assumed that the wordsize used is a power of 2.     * <p>     * @param  x  word to rotate     * @param  y    number of bits to rotate % 32     */    private int rotateLeft(int x, int y)    {        return ((x << (y & (32-1))) | (x >>> (32 - (y & (32-1)))));    }    /**     * Perform a right "spin" of the word. The rotation of the given     * word <em>x</em> is rotated left by <em>y</em> bits.     * Only the <em>lg(32)</em> low-order bits of <em>y</em>     * are used to determine the rotation amount. Here it is      * assumed that the wordsize used is a power of 2.     * <p>     * @param  x  word to rotate     * @param  y    number of bits to rotate % 32     */    private int rotateRight(int x, int y)    {        return ((x >>> (y & (32-1))) | (x << (32 - (y & (32-1)))));    }    private int bytesToWord(        byte[]  src,        int     srcOff)    {        return (src[srcOff] & 0xff) | ((src[srcOff + 1] & 0xff) << 8)            | ((src[srcOff + 2] & 0xff) << 16) | ((src[srcOff + 3] & 0xff) << 24);    }    private void wordToBytes(        int    word,        byte[]  dst,        int     dstOff)    {        dst[dstOff] = (byte)word;        dst[dstOff + 1] = (byte)(word >> 8);        dst[dstOff + 2] = (byte)(word >> 16);        dst[dstOff + 3] = (byte)(word >> 24);    }}