SimpleCrypto.java

/*
 * Copyright (C) 2012-2016 The Android Money Manager Ex Project Team
 *
 * 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.money.manager.ex.passcode;

import android.os.Build;

import java.nio.charset.StandardCharsets;
import java.security.SecureRandom;
import java.security.spec.KeySpec;

import javax.crypto.Cipher;
import javax.crypto.KeyGenerator;
import javax.crypto.SecretKey;
import javax.crypto.SecretKeyFactory;
import javax.crypto.spec.PBEKeySpec;
import javax.crypto.spec.SecretKeySpec;

import timber.log.Timber;

/**
 * http://www.androidsnippets.com/encryptdecrypt-strings
 * http://android-developers.blogspot.co.at/2016/06/security-crypto-provider-deprecated-in.html
 * @author ferenc.hechler
 */
public class SimpleCrypto {

	public static String encrypt(String seed, String cleartext) throws Exception {
		byte[] rawKey = getRawKey(seed.getBytes());

        byte[] result = encrypt(rawKey, cleartext.getBytes());
		return toHex(result);
	}
	
	public static String decrypt(String seed, String encrypted) throws Exception {
		byte[] rawKey = getRawKey(seed.getBytes());
		byte[] enc = toByte(encrypted);
		byte[] result = decrypt(rawKey, enc);
		return new String(result);
	}

	private static byte[] getRawKey(byte[] seed) throws Exception {
		KeyGenerator kgen = KeyGenerator.getInstance("AES");
		SecureRandom sr;
		if (Build.VERSION.SDK_INT <= Build.VERSION_CODES.JELLY_BEAN) {
			sr = SecureRandom.getInstance("SHA1PRNG");
		} else {
			sr = SecureRandom.getInstance( "SHA1PRNG", "Crypto" );
		}
		sr.setSeed(seed);
	    kgen.init(128, sr); // 192 and 256 bits may not be available
	    SecretKey skey = kgen.generateKey();
	    byte[] raw = skey.getEncoded();
	    return raw;
	}

	
	private static byte[] encrypt(byte[] raw, byte[] clear) throws Exception {
	    SecretKeySpec skeySpec = new SecretKeySpec(raw, "AES");
		Cipher cipher = Cipher.getInstance("AES");
	    cipher.init(Cipher.ENCRYPT_MODE, skeySpec);
	    byte[] encrypted = cipher.doFinal(clear);
		return encrypted;
	}

	private static byte[] decrypt(byte[] raw, byte[] encrypted) throws Exception {
	    SecretKeySpec skeySpec = new SecretKeySpec(raw, "AES");
		Cipher cipher = Cipher.getInstance("AES");
	    cipher.init(Cipher.DECRYPT_MODE, skeySpec);
	    byte[] decrypted = cipher.doFinal(encrypted);
		return decrypted;
	}

	public static String toHex(String txt) {
		return toHex(txt.getBytes());
	}
	public static String fromHex(String hex) {
		return new String(toByte(hex));
	}
	
	public static byte[] toByte(String hexString) {
		int len = hexString.length()/2;
		byte[] result = new byte[len];
		for (int i = 0; i < len; i++)
			result[i] = Integer.valueOf(hexString.substring(2*i, 2*i+2), 16).byteValue();
		return result;
	}

	public static String toHex(byte[] buf) {
		if (buf == null)
			return "";
		StringBuffer result = new StringBuffer(2*buf.length);
		for (int i = 0; i < buf.length; i++) {
			appendHex(result, buf[i]);
		}
		return result.toString();
	}
	private final static String HEX = "0123456789ABCDEF";
	private static void appendHex(StringBuffer sb, byte b) {
		sb.append(HEX.charAt((b>>4)&0x0f)).append(HEX.charAt(b&0x0f));
	}
}