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package org.bouncycastle.crypto.engines;

import org.bouncycastle.crypto.BlockCipher;
import org.bouncycastle.crypto.CipherParameters;
import org.bouncycastle.crypto.DataLengthException;
import org.bouncycastle.crypto.OutputLengthException;
import org.bouncycastle.crypto.params.KeyParameter;

/**
 * An RC6 engine.
 */
public class RC6Engine
    implements BlockCipher
{
    private static final int wordSize = 32;
    private static final int bytesPerWord = wordSize / 8;

    /*
     * the number of rounds to perform
     */
    private static final int _noRounds = 20;

    /*
     * the expanded key array of size 2*(rounds + 1)
     */
    private int _S[];

    /*
     * our "magic constants" for wordSize 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 static final int    LGW = 5;        // log2(32)

    private boolean forEncryption;

    /**
     * Create an instance of the RC6 encryption algorithm
     * and set some defaults
     */
    public RC6Engine()
    {
        _S            = null;
    }

    public String getAlgorithmName()
    {
        return "RC6";
    }

    public int getBlockSize()
    {
        return 4 * bytesPerWord;
    }

    /**
     * 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 KeyParameter))
        {
            throw new IllegalArgumentException("invalid parameter passed to RC6 init - " + params.getClass().getName());
        }

        KeyParameter       p = (KeyParameter)params;
        this.forEncryption = forEncryption;
        setKey(p.getKey());
    }

    public int processBlock(
        byte[]  in,
        int     inOff,
        byte[]  out,
        int     outOff)
    {
        int blockSize = getBlockSize();
        if (_S == null)
        {
            throw new IllegalStateException("RC6 engine not initialised");
        }
        if ((inOff + blockSize) > in.length)
        {
            throw new DataLengthException("input buffer too short");
        }
        if ((outOff + blockSize) > out.length)
        {
            throw new OutputLengthException("output buffer too short");
        }

        return (forEncryption)
            ?   encryptBlock(in, inOff, out, outOff) 
            :   decryptBlock(in, inOff, out, outOff);
    }

    public void reset()
    {
    }

    /**
     * Re-key the cipher.
     * 

* @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 = wordSize/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. // // compute number of dwords int c = (key.length + (bytesPerWord - 1)) / bytesPerWord; if (c == 0) { c = 1; } int[] L = new int[(key.length + bytesPerWord - 1) / bytesPerWord]; // load all key bytes into array of key dwords for (int i = key.length - 1; i >= 0; i--) { L[i / bytesPerWord] = (L[i / bytesPerWord] << 8) + (key[i] & 0xff); } // // Phase 2: // Key schedule is placed in a array of 2+2*ROUNDS+2 = 44 dwords. // 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+2*_noRounds+2]; _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; int 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; } } private int encryptBlock( byte[] in, int inOff, byte[] out, int outOff) { // load A,B,C and D registers from in. int A = bytesToWord(in, inOff); int B = bytesToWord(in, inOff + bytesPerWord); int C = bytesToWord(in, inOff + bytesPerWord*2); int D = bytesToWord(in, inOff + bytesPerWord*3); // Do pseudo-round #0: pre-whitening of B and D B += _S[0]; D += _S[1]; // perform round #1,#2 ... #ROUNDS of encryption for (int i = 1; i <= _noRounds; i++) { int t = 0,u = 0; t = B*(2*B+1); t = rotateLeft(t,5); u = D*(2*D+1); u = rotateLeft(u,5); A ^= t; A = rotateLeft(A,u); A += _S[2*i]; C ^= u; C = rotateLeft(C,t); C += _S[2*i+1]; int temp = A; A = B; B = C; C = D; D = temp; } // do pseudo-round #(ROUNDS+1) : post-whitening of A and C A += _S[2*_noRounds+2]; C += _S[2*_noRounds+3]; // store A, B, C and D registers to out wordToBytes(A, out, outOff); wordToBytes(B, out, outOff + bytesPerWord); wordToBytes(C, out, outOff + bytesPerWord*2); wordToBytes(D, out, outOff + bytesPerWord*3); return 4 * bytesPerWord; } private int decryptBlock( byte[] in, int inOff, byte[] out, int outOff) { // load A,B,C and D registers from out. int A = bytesToWord(in, inOff); int B = bytesToWord(in, inOff + bytesPerWord); int C = bytesToWord(in, inOff + bytesPerWord*2); int D = bytesToWord(in, inOff + bytesPerWord*3); // Undo pseudo-round #(ROUNDS+1) : post whitening of A and C C -= _S[2*_noRounds+3]; A -= _S[2*_noRounds+2]; // Undo round #ROUNDS, .., #2,#1 of encryption for (int i = _noRounds; i >= 1; i--) { int t=0,u = 0; int temp = D; D = C; C = B; B = A; A = temp; t = B*(2*B+1); t = rotateLeft(t, LGW); u = D*(2*D+1); u = rotateLeft(u, LGW); C -= _S[2*i+1]; C = rotateRight(C,t); C ^= u; A -= _S[2*i]; A = rotateRight(A,u); A ^= t; } // Undo pseudo-round #0: pre-whitening of B and D D -= _S[1]; B -= _S[0]; wordToBytes(A, out, outOff); wordToBytes(B, out, outOff + bytesPerWord); wordToBytes(C, out, outOff + bytesPerWord*2); wordToBytes(D, out, outOff + bytesPerWord*3); return 4 * bytesPerWord; } ////////////////////////////////////////////////////////////// // // PRIVATE Helper Methods // ////////////////////////////////////////////////////////////// /** * Perform a left "spin" of the word. The rotation of the given * word x is rotated left by y bits. * Only the lg(wordSize) low-order bits of y * are used to determine the rotation amount. Here it is * assumed that the wordsize used is 32. *

* @param x word to rotate * @param y number of bits to rotate % wordSize */ private int rotateLeft(int x, int y) { return (x << y) | (x >>> -y); } /** * Perform a right "spin" of the word. The rotation of the given * word x is rotated left by y bits. * Only the lg(wordSize) low-order bits of y * are used to determine the rotation amount. Here it is * assumed that the wordsize used is a power of 2. *

* @param x word to rotate * @param y number of bits to rotate % wordSize */ private int rotateRight(int x, int y) { return (x >>> y) | (x << -y); } private int bytesToWord( byte[] src, int srcOff) { int word = 0; for (int i = bytesPerWord - 1; i >= 0; i--) { word = (word << 8) + (src[i + srcOff] & 0xff); } return word; } private void wordToBytes( int word, byte[] dst, int dstOff) { for (int i = 0; i < bytesPerWord; i++) { dst[i + dstOff] = (byte)word; word >>>= 8; } } }





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