encryption decryption ideas and sample code

// CALL LIKE THIS :
//string str = Encrypt(s_querystring, "#@$&%")
//string str = Decrypt(s_querystring, "#@$&%");
//--------------------------------------------//

public static string Encrypt(string stringToEncrypt, string encryptionKey)
        {
            byte[] key = { };
            byte[] IV = { 10, 20, 30, 40, 50, 60, 70, 80 };
            byte[] inputByteArray;

            try
            {
                key = Encoding.UTF8.GetBytes(encryptionKey.Substring(0, 8));
                DESCryptoServiceProvider des = new DESCryptoServiceProvider();
                inputByteArray = Encoding.UTF8.GetBytes(stringToEncrypt);
                MemoryStream ms = new MemoryStream();
                CryptoStream cs = new CryptoStream(ms, des.CreateEncryptor(key, IV), CryptoStreamMode.Write);
                cs.Write(inputByteArray, 0, inputByteArray.Length);
                cs.FlushFinalBlock();
                return Convert.ToBase64String(ms.ToArray()).Replace("+", "-").Replace("/", "_"); ;
            }
            catch (System.Exception ex)
            {
                return (string.Empty);
            }
        }

        public static string Decrypt(string stringToDecrypt, string sEncryptionKey)
        {
            byte[] key = { };
            byte[] IV = { 10, 20, 30, 40, 50, 60, 70, 80 };
            byte[] inputByteArray = new byte[stringToDecrypt.Length];
            try
            {
                stringToDecrypt = stringToDecrypt.Replace("-", "+").Replace("_", "/");
                key = Encoding.UTF8.GetBytes(sEncryptionKey.Substring(0, 8));
                DESCryptoServiceProvider des = new DESCryptoServiceProvider();
                inputByteArray = Convert.FromBase64String(stringToDecrypt);
                MemoryStream ms = new MemoryStream();
                CryptoStream cs = new CryptoStream(ms, des.CreateDecryptor(key, IV), CryptoStreamMode.Write);
                cs.Write(inputByteArray, 0, inputByteArray.Length);
                cs.FlushFinalBlock();
                Encoding encoding = Encoding.UTF8;
                return encoding.GetString(ms.ToArray());
            }
            catch (System.Exception ex)
            {
                return (string.Empty);
            }
        }