de.schlichtherle.truezip.zip.WinZipAesCipher Maven / Gradle / Ivy

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/*
 * Copyright (C) 2005-2015 Schlichtherle IT Services.
 * All rights reserved. Use is subject to license terms.
 */
package de.schlichtherle.truezip.zip;

import de.schlichtherle.truezip.crypto.SICSeekableBlockCipher;
import org.bouncycastle.crypto.DataLengthException;
import org.bouncycastle.crypto.engines.AESFastEngine;

/**
 * Implements Counter (CTR) mode (alias Segmented Integer Counter - SIC)
 * on top of an AES engine.
 * This class is almost identical to {@link SICSeekableBlockCipher} except that
 * the block counter is incremented before updating the cipher input
 * in little endian order.
 *
 * @since   TrueZIP 7.3
 * @see     A Password Based File Encyption Utility (Dr. Gladman)
 * @author  Christian Schlichtherle
 */
final class WinZipAesCipher extends SICSeekableBlockCipher {

    /**
     * Constructs a new block cipher mode for use with WinZip AES.
     * This constructor uses an {@link AESFastEngine} as the underlying block
     * cipher.
     */
    WinZipAesCipher() {
        super(new AESFastEngine());
    }

    @Override
    public int processBlock(
            final byte[] in,
            int inOff,
            final byte[] out,
            int outOff)
    throws DataLengthException, IllegalStateException {
        incCounter();
        this.cipher.processBlock(this.cipherIn, 0, this.cipherOut, 0);

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

        return blockSize;
    }

    private void incCounter() {
        final int blockSize = this.blockSize;
        long blockCounter = ++this.blockCounter; // pre-increment the block counter!
        for (int i = 0; i < blockSize; i++) { // little endian order!
            blockCounter += IV[i] & 0xff;
            this.cipherIn[i] = (byte) blockCounter;
            blockCounter >>>= 8;
        }
    }
}