Joker Codes Gift Card Decryption Java Implementation

JokerCodesSecurityUtil.java

import java.security.InvalidAlgorithmParameterException;
import java.security.InvalidKeyException;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.Base64;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.crypto.BadPaddingException;
import javax.crypto.Cipher;
import javax.crypto.IllegalBlockSizeException;
import javax.crypto.NoSuchPaddingException;
import javax.crypto.SecretKey;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.SecretKeySpec;

/**
 *
 * @author Mohammed
 */
public class JokerCodesSecurityUtil {
    
    public static String decryptGiftCardNumber(String encrypted, String secretKey, String secretIv) {
        try {
            encrypted = new String(Base64.getDecoder().decode(encrypted));
            
            MessageDigest digest = MessageDigest.getInstance("SHA-256");
            
            String key = bytesToHex(digest.digest(secretKey.getBytes())).substring(0, 32);
            String iv = bytesToHex(digest.digest(secretIv.getBytes())).substring(0, 16);
            
            SecretKeySpec secretKeySpec = new SecretKeySpec(key.getBytes(), "AES");
            
            String returnVal = decrypt("AES/CBC/PKCS5Padding", encrypted, secretKeySpec, new IvParameterSpec(iv.getBytes()));
            
            return returnVal;
        } catch (Exception ex) {
            Logger.getLogger(JokerCodesSecurityUtil.class.getName()).log(Level.SEVERE, null, ex);
            
            throw new RuntimeException("Error while decrypting data");
        }
    }

    private static String bytesToHex(byte[] hash) {
        StringBuilder hexString = new StringBuilder(2 * hash.length);
        for (int i = 0; i < hash.length; i++) {
            String hex = Integer.toHexString(0xff & hash[i]);
            if (hex.length() == 1) {
                hexString.append('0');
            }
            hexString.append(hex);
        }
        return hexString.toString();
    }

    private static String decrypt(String algorithm, String cipherText, SecretKey key,
            IvParameterSpec iv) throws NoSuchPaddingException, NoSuchAlgorithmException,
            InvalidAlgorithmParameterException, InvalidKeyException,
            BadPaddingException, IllegalBlockSizeException {

        Cipher cipher = Cipher.getInstance(algorithm);
        cipher.init(Cipher.DECRYPT_MODE, key, iv);

        byte[] plainText = cipher.doFinal(Base64.getDecoder()
                .decode(cipherText));

        return new String(plainText);
    }
}