Token.java

/*
 Swisscom Safe Connect
 Copyright (C) 2014 Swisscom

 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/>.
*/
package com.swisscom.safeconnect.security;

import java.io.UnsupportedEncodingException;
import java.net.URLEncoder;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

import android.util.Log;

import com.swisscom.safeconnect.BuildConfig;
import com.swisscom.safeconnect.utils.Config;

public class Token {
	
	private static String bytesToHex(byte[] a) {
		StringBuilder sb = new StringBuilder();
		for(byte b: a)
			sb.append(String.format("%02x", b&0xff));
		return sb.toString();
	}
	
	/**
	 * will generate a token for the specified data
	 * @param data data to be sent
	 * @return token that the server will check to prove the validity of the data
	 */
	public static String generateToken(String phoneNumber, String data) {
		if (data == null) throw new NullPointerException("data cannot be null");

		String preKey = "";
		byte[] key = hash(preKey);
		
		Encryptor enc = new Encryptor(key, hash(data));

		long timestamp = System.currentTimeMillis();

        try {
            return URLEncoder.encode(enc.encrypt(String.valueOf(timestamp)), "UTF-8");
        } catch (UnsupportedEncodingException e) {
            if (BuildConfig.DEBUG) Log.e(Config.TAG, "encoding error", e);
            return "";
        }
    }
	
	public static byte[] hash(String data) {
		MessageDigest digest = null;
		
		try {
			digest = MessageDigest.getInstance("SHA-256");
		} catch (NoSuchAlgorithmException e) {
			if (BuildConfig.DEBUG) Log.e(Config.TAG, "digest error ", e);
		}
		
		if (digest != null) {
			digest.update(data.getBytes());
			return digest.digest();
		}
		
		return new byte[32];
	}
}