Lampiran 8 : Class Mode Enkripsi CBC (CBCBlockCipher.java)

8. Lampiran 8 : Class Mode Enkripsi CBC (CBCBlockCipher.java)

package org.bouncycastle.crypto.modes;

import org.bouncycastle.crypto.BlockCipher; import org.bouncycastle.crypto.CipherParameters; import org.bouncycastle.crypto.DataLengthException; import org.bouncycastle.crypto.params.ParametersWithIV; import org.bouncycastle.util.Arrays;

/** * implements Cipher-Block-Chaining (CBC) mode on top of a simple cipher. */

public class CBCBlockCipher implements BlockCipher { private byte[] IV; private byte[] cbcV; private byte[] cbcNextV;

private int blockSize; private BlockCipher cipher = null; private boolean encrypting;

/** * Basic constructor. * * @param cipher the block cipher to be used as the basis of

chaining. */ public CBCBlockCipher( BlockCipher cipher) { this.cipher = cipher; this.blockSize = cipher.getBlockSize();

this.IV = new byte[blockSize]; this.cbcV = new byte[blockSize]; this.cbcNextV = new byte[blockSize];

/** * return the underlying block cipher that we are wrapping. * * @return the underlying block cipher that we are wrapping. */ /** * return the underlying block cipher that we are wrapping. * * @return the underlying block cipher that we are wrapping. */

return cipher; }

/** * Initialise the cipher and, possibly, the initialisation vector (IV). * If an IV isn't passed as part of the parameter, the IV will be all zeros. * * @param encrypting if true the cipher is initialised for * encryption, if false for decryption. * @param params the key and other data required by the cipher. * @exception IllegalArgumentException if the params argument is * inappropriate. */

public void init( boolean encrypting, CipherParameters params) throws IllegalArgumentException

{ this.encrypting = encrypting;

if (params instanceof ParametersWithIV) {

ParametersWithIV ivParam = (ParametersWithIV)params; byte[] iv = ivParam.getIV();

if (iv.length != blockSize) {

throw new IllegalArgumentException("initialisation vector must be the same length as block size"); }

System.arraycopy(iv, 0, IV, 0, iv.length);

reset();

cipher.init(encrypting, ivParam.getParameters()); } else {

reset();

cipher.init(encrypting, params); } }

/** * return the algorithm name and mode. * * @return the name of the underlying algorithm followed by "/CBC". */

public String getAlgorithmName() {

return cipher.getAlgorithmName() + "/CBC"; }

/** * return the block size of the underlying cipher. * * @return the block size of the underlying cipher. */

public int getBlockSize() {

return cipher.getBlockSize(); }

/** * Process one block of input from the array in and write it to * the out array. * * @param in the array containing the input data. * @param inOff offset into the in array the data starts at. * @param out the array the output data will be copied into. * @param outOff the offset into the out array the output will start

at. * @exception DataLengthException if there isn't enough data in in, or * space in out. * @exception IllegalStateException if the cipher isn't initialised. * @return the number of bytes processed and produced. */

public int processBlock( byte[] in, int inOff, byte[] out, int outOff) throws DataLengthException, IllegalStateException

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

* reset the chaining vector back to the IV and reset the underlying * cipher. */

public void reset() {

System.arraycopy(IV, 0, cbcV, 0, IV.length); Arrays.fill(cbcNextV, (byte)0);

cipher.reset(); }

/** * Do the appropriate chaining step for CBC mode encryption. * * @param in the array containing the data to be encrypted. * @param inOff offset into the in array the data starts at. * @param out the array the encrypted data will be copied into. * @param outOff the offset into the out array the output will start

at. * @exception DataLengthException if there isn't enough data in in, or * space in out. * @exception IllegalStateException if the cipher isn't initialised. * @return the number of bytes processed and produced. */

private int encryptBlock( byte[] in, int inOff, byte[] out, int outOff) throws DataLengthException, IllegalStateException

{ if ((inOff + blockSize) > in.length) {

throw new DataLengthException("input buffer too short"); }

/* * XOR the cbcV and the input, * then encrypt the cbcV */

for (int i = 0; i < blockSize; i++) {

cbcV[i] ^= in[inOff + i]; }

int length = cipher.processBlock(cbcV, 0, out, outOff);

/* * copy ciphertext to cbcV */

System.arraycopy(out, outOff, cbcV, 0, cbcV.length);

return length; }

/** * Do the appropriate chaining step for CBC mode decryption. * * @param in the array containing the data to be decrypted. * @param inOff offset into the in array the data starts at. * @param out the array the decrypted data will be copied into. * @param outOff the offset into the out array the output will start

at. * @exception DataLengthException if there isn't enough data in in, or * space in out. * @exception IllegalStateException if the cipher isn't initialised. * @return the number of bytes processed and produced. */

private int decryptBlock( byte[] in, int inOff, byte[] out, int outOff) throws DataLengthException, IllegalStateException

{ if ((inOff + blockSize) > in.length) {

throw new DataLengthException("input buffer too short"); }

System.arraycopy(in, inOff, cbcNextV, 0, blockSize);

int length = cipher.processBlock(in, inOff, out, outOff);

/* * XOR the cbcV and the output */

for (int i = 0; i < blockSize; i++) {

out[outOff + i] ^= cbcV[i]; }

/* * swap the back up buffer into next position

100

*/ byte[] tmp;

tmp = cbcV; cbcV = cbcNextV; cbcNextV = tmp;

return length; } }