AES encryption helper

Recently I used AES encryption using Java. AES is an efficient algorithm for encryption. You can benefit from the helper class I wrote to perform the encryption and decryption using AES.

To read mode about the AES encryption please follow this link

AES Encryption Wiki

Following is link to AES Helper source code

AES Helper on github

Java source code for the helper class

package com.techmali.aes;


import java.security.InvalidKeyException;
import java.security.NoSuchAlgorithmException;

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


public class AESHelper
{
    private static final char hexDigits[] = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F' };

    private static SecretKeySpec getSecretKey(final String myKey) throws NoSuchPaddingException, NoSuchAlgorithmException, InvalidKeyException {
        return new SecretKeySpec(HexFromString(myKey), "AES");
    }

    private static byte[] HexFromString(String s) {
        int i = s.length();
        byte abyte0[] = new byte[(i + 1) / 2];
        int j = 0;
        int k = 0;
        if (i % 2 == 1)
            abyte0[k++] = (byte) HexFromDigit(s.charAt(j++));
        while (j < i)
            abyte0[k++] = (byte) (HexFromDigit(s.charAt(j++)) << 4 | HexFromDigit(s.charAt(j++)));
        return abyte0;
    }

    private static int HexFromDigit(char c) {
        if (c >= '0' && c <= '9')
            return c - 48;
        if (c >= 'A' && c <= 'F')
            return (c - 65) + 10;
        if (c >= 'a' && c <= 'f')
            return (c - 97) + 10;
        else
            throw new IllegalArgumentException("invalid hex digit '" + c + "'");
    }

    public static String encrypt(final String strToEncrypt, final String secretKey)
    {
        try
        {
            final SecretKeySpec key = getSecretKey(secretKey);
            final Cipher cipher = Cipher.getInstance("AES");
            cipher.init(Cipher.ENCRYPT_MODE, key);
            final byte encstr[] = cipher.doFinal(strToEncrypt.getBytes());
            return HexToString(encstr);
        }
        catch (Exception e)
        {
            throw new RuntimeException("Error while encrypting message:" + e.getMessage());
        }
    }

    private static String HexToString(final byte bytes[]) {
        return HexToString(bytes, 0, bytes.length);
    }

    private static String HexToString(final byte bytes[], final int i, final int j) {
        char ac[] = new char[j * 2];
        int k = 0;
        for (int l = i; l < i + j; l++) {
            byte byte0 = bytes[l];
            ac[k++] = hexDigits[byte0 >>> 4 & 0xf];
            ac[k++] = hexDigits[byte0 & 0xf];
        }

        return new String(ac);
    }


    public static String decrypt(final String strToDecrypt, final String secretKey)
    {
        try {
            final SecretKeySpec key = getSecretKey(secretKey);
            final Cipher cipher = Cipher.getInstance("AES");
            cipher.init(Cipher.DECRYPT_MODE, key);
            if (strToDecrypt != null && !strToDecrypt.equals("")) {
                byte encStr[] = cipher.doFinal(HexFromString(strToDecrypt));
                return new String(encStr).trim();
            } else {
                return "";
            }
        } catch (NoSuchPaddingException | NoSuchAlgorithmException | IllegalBlockSizeException | InvalidKeyException | BadPaddingException e) {
            throw new RuntimeException("Error while decrypting message:" + e.getMessage());
        }
    }
}