/// <summary>
        /// Generate a Totp using provided binary data.
        /// </summary>
        /// <param name="key">Binary data.</param>
        /// <returns>Time-based One Time Password.</returns>
        public string Generate(byte[] key)
        {
            System.Security.Cryptography.HMACSHA1 hmac = new System.Security.Cryptography.HMACSHA1(key, true); //Instanciates a new hash provider with a key.
            byte[] hash = hmac.ComputeHash(GetBytes((ulong)Counter));                                          //Generates hash from key using counter.
            hmac.Clear();                                                                                      //Clear hash instance securing the key.

            int offset = hash[hash.Length - 1] & 0xf;                                                          //Math.
            int binary =                                                                                       //Math.
                         ((hash[offset] & 0x7f) << 24)                                                         //Math.
                         | ((hash[offset + 1] & 0xff) << 16)                                                   //Math.
                         | ((hash[offset + 2] & 0xff) << 8)                                                    //Math.
                         | (hash[offset + 3] & 0xff);                                                          //Math.

            int password = binary % (int)Math.Pow(10, _Length);                                                //Math.

            return(password.ToString(new string('0', _Length)));                                               //Math.
        }
        /// <summary>
        /// Generate a Totp using provided binary data.
        /// </summary>
        /// <param name="key">Binary data.</param>
        /// <returns>Time-based One Time Password.</returns>
        public string Generate(byte[] key)
        {
            System.Security.Cryptography.HMACSHA1 hmac = new System.Security.Cryptography.HMACSHA1(key, true); //Instanciates a new hash provider with a key.
            byte[] hash = hmac.ComputeHash(GetBytes((ulong)Counter)); //Generates hash from key using counter.
            hmac.Clear(); //Clear hash instance securing the key.

            int offset = hash[hash.Length - 1] & 0xf;           //Math.
            int binary =                                        //Math.
                ((hash[offset] & 0x7f) << 24)                   //Math.
                | ((hash[offset + 1] & 0xff) << 16)             //Math.
                | ((hash[offset + 2] & 0xff) << 8)              //Math.
                | (hash[offset + 3] & 0xff);                    //Math.

            int password = binary % (int)Math.Pow(10, _Length); //Math.
            return password.ToString(new string('0', _Length)); //Math.
        }