Android AES

/*
 * 참조한 문서
 * http://stackoverflow.com/questions/13389870/android-4-2-broke-my-aes-encrypt-decrypt-code
 */
public class SimpleCrypto {
    private final static String HEX = "0123456789ABCDEF";
    private final static int JELLY_BEAN_4_2 = 17;

    // 암호화에 사용할 키. 원하는 값으로 바꿔주자.
    private final static byte[] key = {(byte)0x00, (byte)0x00, (byte)0x00, (byte)0x00, (byte)0x00, (byte)0x00, (byte)0x00, (byte)0x00, (byte)0x00, (byte)0x00, (byte)0x00, (byte)0x00, (byte)0x00, (byte)0x00, (byte)0x00, (byte)0x00 };

    /**
     * AES 암호화
     * @param seed 암호화에 사용할 seed
     * @param cleartext 암호화 할 문자열
     * @return 암호화된 문자열
     * @throws Exception 암호화 key 사이즈가 192bit 또는 128bit로 감소함.
     */
    public static String encrypt(String seed, String cleartext) throws Exception {
        if (cleartext == null || cleartext == "") return null;
        byte[] rawKey = getRawKey(seed.getBytes());
        byte[] result = encrypt(rawKey, cleartext.getBytes());
        String fromHex = toHex(result);
        String base64 = new String(Base64.encodeToString(fromHex.getBytes(), 0));
        return base64;
    }

    /**
     * AES 복호화
     * @param seed 복호화에 사용할 seed
     * @param encrypted 복호화 할 문자열
     * @return 복호화한 문자열
     * @throws Exception 암호화 key 사이즈가 192bit 또는 128bit로 감소함.
     */
    public static String decrypt(String seed, String encrypted) throws Exception {
        if (encrypted == null || encrypted == "") return null;
        byte[] seedByte = seed.getBytes();
        System.arraycopy(seedByte, 0, key, 0, ((seedByte.length < 16) ? seedByte.length : 16));
        String base64 = new String(Base64.decode(encrypted, 0));
        byte[] rawKey = getRawKey(seedByte);
        byte[] enc = toByte(base64);
        byte[] result = decrypt(rawKey, enc);
        return new String(result);
    }


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

    public static byte[] decryptBytes(String seed, byte[] encrypted) throws Exception {
        byte[] rawKey = getRawKey(seed.getBytes());
        byte[] result = decrypt(rawKey, encrypted);
        return result;
    }

    private static byte[] getRawKey(byte[] seed) throws Exception {
        KeyGenerator kgen = KeyGenerator.getInstance("AES");
        SecureRandom sr = null;
        if (android.os.Build.VERSION.SDK_INT >= JELLY_BEAN_4_2) {
            sr = SecureRandom.getInstance("SHA1PRNG", "Crypto");
        } else {
            sr = SecureRandom.getInstance("SHA1PRNG");
        }
        sr.setSeed(seed);
        try {
            kgen.init(256, sr);
            // kgen.init(128, sr);
        } catch (Exception e) {
            // Log.w(LOG, "This device doesn't suppor 256bits, trying 192bits.");
            try {
                kgen.init(192, sr);
            } catch (Exception e1) {
                // Log.w(LOG, "This device doesn't suppor 192bits, trying 128bits.");
                kgen.init(128, sr);
            }
        }
        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 static void appendHex(StringBuffer sb, byte b) {
        sb.append(HEX.charAt((b >> 4) & 0x0f)).append(HEX.charAt(b & 0x0f));
    }

}