HmacBlockStream.java

/*
 * Copyright 2017 Brian Pellin.
 *
 * This file is part of KeePassDroid.
 *
 *  KeePassDroid is free software: you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation, either version 2 of the License, or
 *  (at your option) any later version.
 *
 *  KeePassDroid 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 General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with KeePassDroid.  If not, see <http://www.gnu.org/licenses/>.
 *
 */
package com.keepassdroid.stream;

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.security.DigestOutputStream;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

public class HmacBlockStream {
    public static byte[] GetHmacKey64(byte[] key, long blockIndex) {
        MessageDigest hash;
        try {
            hash = MessageDigest.getInstance("SHA-512");
        } catch (NoSuchAlgorithmException e) {
            throw new RuntimeException(e);
        }

        NullOutputStream nos = new NullOutputStream();
        DigestOutputStream dos = new DigestOutputStream(nos, hash);
        LEDataOutputStream leos = new LEDataOutputStream(dos);

        try {
            leos.writeLong(blockIndex);
            leos.write(key);
            leos.close();
        } catch (IOException e) {
            throw new RuntimeException(e);
        }

        byte[] hashKey = hash.digest();
        assert(hashKey.length == 64);

        return hashKey;
    }

}