CcSalted.java

/**
 * The MIT License (MIT)
 *
 * Copyright (c) 2014-2017 Yegor Bugayenko
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included
 * in all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NON-INFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */
package org.takes.facets.auth.codecs;

import com.jcabi.aspects.Tv;
import java.io.IOException;
import java.security.SecureRandom;
import java.util.Random;
import lombok.EqualsAndHashCode;
import org.takes.facets.auth.Identity;

/**
 * Salted codec.
 *
 * <p>The class is immutable and thread-safe.
 *
 * @author Yegor Bugayenko (yegor256@gmail.com)
 * @version $Id: e9c8c847bc8b125f869d866cd30171a67f630089 $
 * @since 0.1
 */
@EqualsAndHashCode
public final class CcSalted implements Codec {

    /**
     * Random generator.
     */
    private static final Random RND = new SecureRandom();

    /**
     * Original codec.
     */
    private final Codec origin;

    /**
     * Ctor.
     * @param codec Original
     */
    public CcSalted(final Codec codec) {
        this.origin = codec;
    }

    @Override
    public byte[] encode(final Identity identity) throws IOException {
        return CcSalted.salt(this.origin.encode(identity));
    }

    @Override
    public Identity decode(final byte[] bytes) throws IOException {
        return this.origin.decode(CcSalted.unsalt(bytes));
    }

    /**
     * Salt the string.
     * @param text Original text to salt
     * @return Salted string
     */
    @SuppressWarnings("PMD.AvoidArrayLoops")
    private static byte[] salt(final byte[] text) {
        final byte size = (byte) CcSalted.RND.nextInt(Tv.TEN);
        final byte[] output = new byte[text.length + (int) size + 2];
        output[0] = size;
        byte sum = (byte) 0;
        for (int idx = 0; idx < (int) size; ++idx) {
            output[idx + 1] = (byte) CcSalted.RND.nextInt();
            sum += output[idx + 1];
        }
        System.arraycopy(text, 0, output, (int) size + 1, text.length);
        output[output.length - 1] = sum;
        return output;
    }

    /**
     * Un-salt the string.
     * @param text Salted text
     * @return Original text
     */
    private static byte[] unsalt(final byte[] text) {
        if (text.length == 0) {
            throw new DecodingException("empty input");
        }
        final int size = text[0];
        if (text.length < size + 2) {
            throw new DecodingException(
                String.format(
                    "not enough bytes for salt, length is %d while %d required",
                    text.length, size + 2
                )
            );
        }
        byte sum = (byte) 0;
        for (int idx = 0; idx < size; ++idx) {
            sum += text[idx + 1];
        }
        if (text[text.length - 1] != sum) {
            throw new DecodingException(
                String.format(
                    "checksum %d failure, while %d expected",
                    text[text.length - 1], sum
                )
            );
        }
        final byte[] output = new byte[text.length - size - 2];
        System.arraycopy(text, size + 1, output, 0, output.length);
        return output;
    }

}