TorHop.java

package tor;

/*
        Tor Research Framework - easy to use tor client library/framework
        Copyright (C) 2014  Dr Gareth Owen <drgowen@gmail.com>
        www.ghowen.me / github.com/drgowen/tor-research-framework

        This program 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 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 General Public License for more details.

        You should have received a copy of the GNU General Public License
        along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/

import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;
import tor.util.TorCircuitException;

import javax.crypto.Cipher;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.SecretKeySpec;
import java.nio.ByteBuffer;
import java.security.GeneralSecurityException;
import java.security.MessageDigest;
import java.util.Arrays;

public class TorHop {
    final static Logger log = LogManager.getLogger();

    byte[] kh = new byte[TorCrypto.HASH_LEN], df = new byte[TorCrypto.HASH_LEN], db = new byte[TorCrypto.HASH_LEN];
    byte[] kf = new byte[TorCrypto.KEY_LEN], kb = new byte[TorCrypto.KEY_LEN];
    public MessageDigest df_md, db_md;
    Cipher encf, encb;
    OnionRouter router;

    /**
     * Creates TorHop object taking derived key data and calculating keys
     *
     * @param kdf Derived key data from created/extended cell
     * @param _kh KH for verification of correct KDF
     * @param _r  Router which this hop represents
     */
    public TorHop(byte kdf[], byte _kh[], OnionRouter _r) throws TorCircuitException {
        router = _r;
        ByteBuffer buf = ByteBuffer.wrap(kdf);
        buf.get(kh);
        buf.get(df);
        buf.get(db);
        buf.get(kf);
        buf.get(kb);

        try {
            df_md = MessageDigest.getInstance("SHA-1");
            df_md.update(df);
            db_md = MessageDigest.getInstance("SHA-1");
            db_md.update(db);

            IvParameterSpec ivSpec = new IvParameterSpec(new byte[]{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0});
            SecretKeySpec keysp = new SecretKeySpec(kf, "AES");
            encf = Cipher.getInstance("AES/CTR/NoPadding");
            encf.init(Cipher.ENCRYPT_MODE, keysp, ivSpec);

            keysp = new SecretKeySpec(kb, "AES");
            encb = Cipher.getInstance("AES/CTR/NoPadding");
            ivSpec = new IvParameterSpec(new byte[]{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0});
            encb.init(Cipher.DECRYPT_MODE, keysp, ivSpec);
        } catch (GeneralSecurityException e) {
            throw new RuntimeException(e);
        }


        if (!Arrays.equals(_kh, kh))
            log.error("hop key setup failed to router: " + router);

        log.debug("Hop added " + router);
    }

    @Override
    public String toString() {
        return "TorHop{" +
                "router=" + router +
                '}';
    }

    public byte[] encrypt(byte[] in) {
        return encf.update(in);
    }

    protected byte[] decrypt(byte[] in) {
        return encb.update(in);
    }

}