BasicFilenameEncryptionStrategy.java

/*
 * EncFS Java Library
 * Copyright (C) 2013 encfs-java authors
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as published
 * by the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Lesser General Public License for more details.
 */
package org.mrpdaemon.sec.encfs;

import java.util.Arrays;


/**
 * Common class for filename encryption strategies.
 */
abstract class BasicFilenameEncryptionStrategy extends FilenameEncryptionStrategy {

    BasicFilenameEncryptionStrategy(EncFSVolume volume, String volumePath, EncFSFilenameEncryptionAlgorithm algorithm) {
        super(volume, volumePath, algorithm);
    }


    /**
     * Actual encryption to be implemented by the subclass.
     */
    protected abstract byte[] encryptConcrete(EncFSVolume volume, byte[] paddedDecFileName, byte[] fileIv) throws EncFSCorruptDataException;


    /**
     * Filename encryption implementation.
     */
    protected String encryptImpl(String fileName) throws EncFSCorruptDataException {
        EncFSVolume volume = getVolume();
        String volumePath = getVolumePath();
        EncFSConfig config = volume.getConfig();

        byte[] decFileName = fileName.getBytes();
        byte[] paddedDecFileName = getPaddedDecFilename(decFileName);
        byte[] chainIv = EncFSCrypto.computeChainedIV(volume, volumePath,
                config);
        byte[] mac16 = getMac16(volume, paddedDecFileName, chainIv);
        byte[] macBytes = EncFSCrypto.getMacBytes(mac16);
        byte[] fileIv = EncFSCrypto.computeFileIV(chainIv, macBytes);

        byte[] encFileName = encryptConcrete(volume, paddedDecFileName, fileIv);

        return getBase256Filename(mac16, encFileName);
    }


    /**
     * Filename padding implementation hook for subclasses.
     */
    protected abstract byte[] getPaddedDecFilename(byte[] decFileName);


    /**
     * Returns the base 256 filename for the given encrypted filename.
     */
    private String getBase256Filename(byte[] mac16, byte[] encFileName) {
        // current versions store the checksum at the beginning (encfs 0.x
        // stored checksums at the end)

        byte[] base256FileName = new byte[encFileName.length+2];
        base256FileName[0] = mac16[0];
        base256FileName[1] = mac16[1];
        System.arraycopy(encFileName, 0, base256FileName, 2, encFileName.length);

        byte[] fileNameOutput = EncFSBase64.encodeEncfs(base256FileName);

        return new String(fileNameOutput);
    }


    /**
     * Returns the mac16 of the given file name.
     */
    private byte[] getMac16(EncFSVolume volume, byte[] paddedDecFileName, byte[] chainIv) {
        if (volume.getConfig().isChainedNameIV()) {
            return EncFSCrypto.mac16(volume.getMAC(), paddedDecFileName, Arrays.copyOf(chainIv, chainIv.length));
        } else {
            return EncFSCrypto.mac16(volume.getMAC(), paddedDecFileName);
        }
    }

}