/// <summary>
        /// ValidateKey method implmentation
        /// </summary>
        public bool ValidateKey(string upn)
        {
            if (string.IsNullOrEmpty(upn))
            {
                return(false);
            }
            string lupn = upn.ToLower();
            string key  = ReadKey(lupn);

            if (string.IsNullOrEmpty(key))
            {
                return(false);
            }
            if (HasStorageInfos(key))
            {
                byte[] crypted = StripStorageInfos(key);
                if (crypted == null)
                {
                    return(false);
                }
                using (var prov = new AES256CNGEncryption(XORSecret))
                {
                    byte[] cleared = prov.GetDecryptedKey(crypted, lupn);

                    if (cleared == null)
                    {
                        return(false); // Key corrupted
                    }
                    if (prov.CheckSum == null)
                    {
                        return(false); // Key corrupted
                    }
                    if (prov.CheckSum.SequenceEqual(CheckSumEncoding.CheckSum(lupn)))
                    {
                        return(true);  // OK
                    }
                    else
                    {
                        return(false); // Key corrupted
                    }
                }
            }
            else
            {
                return(false);
            }
        }
        /// <summary>
        /// ProbeKey method implmentation
        /// </summary>
        public byte[] ProbeKey(string upn)
        {
            if (string.IsNullOrEmpty(upn))
            {
                return(null);
            }
            string lupn = upn.ToLower();
            string key  = ReadKey(lupn);

            if (string.IsNullOrEmpty(key))
            {
                return(null);
            }

            byte[] probed  = null;
            byte[] crypted = StripStorageInfos(key);
            if (crypted == null)
            {
                return(null);
            }
            using (var prov = new AES256CNGEncryption(XORSecret))
            {
                probed = prov.GetDecryptedKey(crypted, lupn);
                if (probed == null)
                {
                    return(null);
                }
            }
            if (probed.Length > MAX_PROBE_LEN)
            {
                byte[] buffer = new byte[MAX_PROBE_LEN];
                Buffer.BlockCopy(probed, 0, buffer, 0, MAX_PROBE_LEN);
                return(buffer);
            }
            else
            {
                return(probed);
            }
        }