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TrueZIP is a Java based Virtual File System (VFS) to enable transparent, multi-threaded read/write access to archive files (ZIP, TAR etc.) as if they were directories. Archive files may be arbitrarily nested and the nesting level is only limited by heap and file system size.

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/*
 * Copyright (C) 2005-2010 Schlichtherle IT Services
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package de.schlichtherle.crypto.modes;

import de.schlichtherle.crypto.*;

import org.bouncycastle.crypto.*;
import org.bouncycastle.crypto.params.*;

/**
 * Implements the Segmented Integer Counter (SIC) alias Counter (CTR) mode
 * on top of a simple block cipher.
 * This code is based on the {@code SICBlockCipher} class
 * (as of version 1.30 of Bouncy Castle's Lightweight API for JDK 1.4),
 * but also allows random access to a block.
 * 
 * @author The Legion of the Bouncy Castle (majority of the code)
 * @author Christian Schlichtherle (optimizations and extension to support seeking)
 * @version $Id: SICSeekableBlockCipher.java,v 1.4 2010/08/20 13:09:55 christian_schlichtherle Exp $
 * @since TrueZIP 3.1
 */
public class SICSeekableBlockCipher implements SeekableBlockCipher {

    private final BlockCipher cipher;
    private final int blockSize;
    private final byte[] IV;
    private final byte[] counter;
    private long blockCounter; // the blockCounter counter
    private final byte[] counterOut;

    /**
     * Basic constructor.
     * 
     * @param c the blockCounter cipher to be used.
     */
    public SICSeekableBlockCipher(BlockCipher c) {
        this.cipher = c;
        this.blockSize = cipher.getBlockSize();
        this.IV = new byte[blockSize];
        this.counter = new byte[blockSize];
        this.counterOut = new byte[blockSize];
    }

    /**
     * return the underlying blockCounter cipher that we are wrapping.
     * 
     * @return the underlying blockCounter cipher that we are wrapping.
     */
    public BlockCipher getUnderlyingCipher() {
        return cipher;
    }

    public void init(boolean forEncryption, CipherParameters params)
    throws IllegalArgumentException {
        if (params instanceof ParametersWithIV) {
          ParametersWithIV ivParams = (ParametersWithIV) params;
          byte[] iv = ivParams.getIV();
          System.arraycopy(iv, 0, IV, 0, IV.length);

          reset();
          cipher.init(true, ivParams.getParameters());
        }
    }

    public String getAlgorithmName() {
        // Must add "/SIC" in order to make BufferedBlockCipher work correctly.
        return cipher.getAlgorithmName() + "/SIC";
    }

    public int getBlockSize() {
        assert blockSize == cipher.getBlockSize();
        return blockSize;
    }

    public int processBlock(
            final byte[] in,
            final int inOff,
            final byte[] out,
            final int outOff)
    throws DataLengthException, IllegalStateException {
        updateCounter();
        cipher.processBlock(counter, 0, counterOut, 0);

        // XOR the counterOut with the plaintext producing the cipher text.
        for (int i = blockSize; --i >= 0; ) {
          out[outOff + i] = (byte)(counterOut[i] ^ in[inOff + i]);
        }

        blockCounter++;

        return blockSize;
    }

    private final void updateCounter() {
        long block = this.blockCounter;
        for (int i = blockSize; --i >= 0; ) {
            block += IV[i] & 0xff;
            counter[i] = (byte) block;
            block >>>= 8;
        }
    }

    public void setBlockCounter(long block) {
        blockCounter = block;
    }

    public long getBlockCounter() {
        return blockCounter;
    }

    public void reset() {
        // Effectively the same as setBlockCounter(0).
        //System.arraycopy(IV, 0, counter, 0, blockSize);
        blockCounter = 0;
        
        cipher.reset();
    }
}