Android Util class to perform encryption/decryption over strings

UtilsEncryption.java

package com.example.encryptiondemo;

import android.util.Log;

import java.io.IOException;
import java.security.InvalidKeyException;
import java.security.NoSuchAlgorithmException;
import java.security.NoSuchProviderException;
import java.security.SecureRandom;

import javax.crypto.BadPaddingException;
import javax.crypto.Cipher;
import javax.crypto.IllegalBlockSizeException;
import javax.crypto.KeyGenerator;
import javax.crypto.NoSuchPaddingException;
import javax.crypto.SecretKey;
import javax.crypto.spec.SecretKeySpec;

/**
 * Util class to perform encryption/decryption over strings. <br/>
 */
public final class UtilsEncryption {
   
    private static final String TAG = UtilsEncryption.class.getName();

    /**
     * Algorithm type
     */
    private static final String ALGORITHM = "AES";

    /**
     * Avoid instantiation. <br/>
     */

    private UtilsEncryption() {
    }

    /**
     * The HEX characters
     */
    private final static String HEX = "0123456789ABCDEF";

    /**
     * Encrypt a given string. <br/>
     *
     * @param cleartext the string to encrypt
     * @return the encrypted string in HEX
     */
    public static String encrypt(String secretKey, String cleartext) {
        try {
            byte[] result = process(secretKey, Cipher.ENCRYPT_MODE, cleartext.getBytes());
            return toHex(result);
        } catch (Exception e) {
            Log.e(TAG, "Encrypt: " + e.getMessage());
            e.printStackTrace();
        }
        return null;
    }

    /**
     * Decrypt a HEX encrypted string. <br/>
     *
     * @param encrypted the HEX string to decrypt
     * @return the decrypted string
     */
    public static String decrypt(String secretKey, String encrypted) {
        try {
            byte[] enc = fromHex(encrypted);
            byte[] result = process(secretKey, Cipher.DECRYPT_MODE, enc);
            return new String(result);
        } catch (Exception e) {
            Log.e(TAG, "Decrypt: " + e.getMessage());
            e.printStackTrace();
        }
        return null;
    }

    /**
     * Get the raw encryption key. <br/>
     *
     * @param secretKey the encryption key
     * @return the SecretKeySpec key
     * @throws NoSuchAlgorithmException
     */
    private static SecretKeySpec generateKey(String secretKey) throws NoSuchAlgorithmException {
        MessageDigest digest = MessageDigest.getInstance("SHA-256");
        byte[] bytes = secretKey.getBytes();
        digest.update(bytes, 0, bytes.length);
        byte[] key = digest.digest();
        return new SecretKeySpec(key, ALGORITHM);
    }

    /**
     * Process the given input with the provided mode. <br/>
     *
     * @param mode  the cipher mode
     * @param value the value to process
     * @return the processed value as byte[]
     * @throws InvalidKeyException
     * @throws IllegalBlockSizeException
     * @throws BadPaddingException
     * @throws NoSuchAlgorithmException
     * @throws NoSuchPaddingException
     * @throws NoSuchProviderException
     */
    private static byte[] process(String secretKey, int mode, byte[] value)
            throws InvalidKeyException, IllegalBlockSizeException, BadPaddingException, NoSuchAlgorithmException,
            NoSuchPaddingException {
        SecretKeySpec skeySpec = generateKey(secretKey);
        Cipher cipher = Cipher.getInstance(ALGORITHM);
        cipher.init(mode, keySpec);
        return cipher.doFinal(value);
    }

    /**
     * Decode an HEX encoded string into a byte[]. <br/>
     *
     * @param value the HEX string value
     * @return the decoded byte[]
     */
    private static byte[] fromHex(String value) {
        int len = value.length() / 2;
        byte[] result = new byte[len];
        for (int i = 0; i < len; i++) {
            result[i] = Integer.valueOf(value.substring(2 * i, 2 * i + 2), 16).byteValue();
        }
        return result;
    }

    /**
     * Encode a byte[] into an HEX string. <br/>
     *
     * @param value the byte[] value
     * @return the HEX encoded string
     */
    private static String toHex(byte[] value) {
        if (value == null) {
            return "";
        }
        StringBuilder result = new StringBuilder(2 * value.length);
        for (byte b : value) {
            result.append(HEX.charAt((b >> 4) & 0x0f));
            result.append(HEX.charAt(b & 0x0f));
        }
        return result.toString();
    }
}