3DES (ECB) implementation in Java

TripleDES.java

import javax.crypto.*;
import javax.crypto.spec.DESKeySpec;
import java.util.Arrays;

public class TripleDES {

    enum MODE {
        ENCRYPT(0), DECRYPT(1);
        int code;

        MODE(int code) {
            this.code = code;
        }
    }

    public static byte[] encrypt(String plaintext, String rawkey) throws Exception {
        return _trip(plaintext.getBytes(), rawkey.getBytes(), MODE.ENCRYPT);
    }

    public static String decrypt(byte[] encrypted, String rawkey) throws Exception {
        String res = "";

        for (byte b : _trip(encrypted, rawkey.getBytes(), MODE.DECRYPT))
            res += String.format("%c", b);

        return res;
    }

    private static SecretKey prepKey(byte[] key) throws Exception {
        DESKeySpec dks = new DESKeySpec(key);
        SecretKeyFactory skf = SecretKeyFactory.getInstance("DES");
        return skf.generateSecret(dks);
    }

    private static byte[] _trip(byte[] input, byte[] key, MODE mode) throws Exception {
        int process[][] = {
                {Cipher.ENCRYPT_MODE, Cipher.DECRYPT_MODE, Cipher.ENCRYPT_MODE},  // encrypt
                {Cipher.DECRYPT_MODE, Cipher.ENCRYPT_MODE, Cipher.DECRYPT_MODE}}; // decrypt
        byte[] res = input;

        for (int i = 0; i < 3; i++)
            res = _digest(res, Arrays.copyOfRange(key, 0 * 8, (i + 1) * 8), process[mode.code][i]);

        return res;
    }

    private static byte[] _digest(byte[] plain, byte[] key, int mode) throws Exception {
        Cipher cipher = Cipher.getInstance("DES");
        cipher.init(mode, prepKey(key));
        return cipher.doFinal(plain);
    }

    public static void main(String[] args) {
        String plaintext = "Did you hear about the restaurant on the moon?",
                passphrase = "Good food, no atmosphere";
        try {
            byte[] encrypted = TripleDES.encrypt(plaintext, passphrase);
            System.out.println(TripleDES.decrypt(encrypted, passphrase));

        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}