Lampiran 10 : Class Mode Enkripsi OFB (OFBBlockCipher.java)
10. Lampiran 10 : Class Mode Enkripsi OFB (OFBBlockCipher.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;
/** * implements a Output-FeedBack (OFB) mode on top of a simple cipher. */
public class OFBBlockCipher implements BlockCipher { private byte[] IV; private byte[] ofbV; private byte[] ofbOutV;
private final int blockSize; private final BlockCipher cipher;
/** * Basic constructor. * * @param cipher the block cipher to be used as the basis of the * feedback mode. * @param blockSize the block size in bits (note: a multiple of 8) */
public OFBBlockCipher( BlockCipher cipher, int blockSize)
{ this.cipher = cipher; this.blockSize = blockSize / 8;
this.IV = new byte[cipher.getBlockSize()]; this.ofbV = new byte[cipher.getBlockSize()]; this.ofbOutV = new byte[cipher.getBlockSize()];
/** * return the underlying block cipher that we are wrapping. * * @return the underlying block cipher that we are wrapping. */
public BlockCipher getUnderlyingCipher() {
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.
* An IV which is too short is handled in FIPS compliant fashion. * * @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, //ignored by this OFB mode CipherParameters params) throws IllegalArgumentException
{ if (params instanceof ParametersWithIV) {
ParametersWithIV ivParam = (ParametersWithIV)params; byte[] iv = ivParam.getIV();
if (iv.length < IV.length) {
// prepend the supplied IV with zeros (per FIPS PUB 81) System.arraycopy(iv, 0, IV, IV.length - iv.length, iv.length); for (int i = 0; i < IV.length - iv.length; i++) {
IV[i] = 0; } } else {
System.arraycopy(iv, 0, IV, 0, IV.length); }
reset();
cipher.init(true, ivParam.getParameters());
else {
reset();
cipher.init(true, params); } }
/** * return the algorithm name and mode. * * @return the name of the underlying algorithm followed by "/OFB" * and the block size in bits */
public String getAlgorithmName() {
return cipher.getAlgorithmName() + "/OFB" + (blockSize * 8);
/** * return the block size we are operating at (in bytes). * * @return the block size we are operating at (in bytes). */
public int getBlockSize() {
return blockSize; }
/** * 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,
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byte[] out, int outOff) throws DataLengthException, IllegalStateException
{ if ((inOff + blockSize) > in.length) {
throw new DataLengthException("input buffer too short"); }
if ((outOff + blockSize) > out.length) {
throw new DataLengthException("output buffer too short"); }
cipher.processBlock(ofbV, 0, ofbOutV, 0);
// // XOR the ofbV with the plaintext producing the cipher text (and // the next input block). // for (int i = 0; i < blockSize; i++) {
out[outOff + i] = (byte)(ofbOutV[i] ^ in[inOff + i]);
// // change over the input block. // System.arraycopy(ofbV,
0, ofbV.length - blockSize); System.arraycopy(ofbOutV, 0, ofbV, ofbV.length - blockSize, blockSize);
blockSize,
ofbV,
return blockSize; }
/** * reset the feedback vector back to the IV and reset the underlying * cipher. */
public void reset() {
System.arraycopy(IV, 0, ofbV, 0, IV.length);
cipher.reset(); } }