Shift Cipher with variable length key

static void Main(string[] args)
        {
            Console.Write("Please enter your message (no spaces, they will be removed): ");
            var message = Console.ReadLine();
            message = message.ToLower().Replace(" ", "");
            Console.Write("Enter your encryption key (number series)");
            var key = Console.ReadLine();
            var encoded = Caesar(message, KeyToArray(key, true), true);
            Console.WriteLine("Your encoded message: " + encoded + "\n\n\n");

            Console.WriteLine("Switch sides, your are the receiver.  Encoded message already put in");

            Console.Write("Enter your key length:");
            var length = Int32.Parse(s: Console.ReadLine());
            var decode = Caesar(encoded, KeyToArray(encoded.Substring(0,length), false), false);
            Console.Write("Message decoded: " + decode);

            Console.Read();
        }

        private static int[] KeyToArray(string key, bool Encode)
        {
            var result = new int[key.Length];
            for (var i = 0; i < key.Length; i++)
                result[i] = Encode ? Int32.Parse(key.Substring(i, 1)) : -(key.Substring(i, 1).ToCharArray()[0] - 96);
            return result;
        }

        static string Caesar(string value, int[] shift, bool Encode)
        {
            var s = 0;
            var startIndex = Encode ? 0 : shift.Length;
            var shiftLength = shift.Length;
            char[] buffer = value.ToCharArray(startIndex, value.Length - startIndex);
            var key = "";

            for (int x = 0; x < shiftLength; x++)
            {
                key += (char) (shift[x] + 96);
            }
            for (int i = 0; i < buffer.Length; i++)
            {
                char letter = buffer[i];
                letter = (char)(letter + shift[s]);
                if (letter > 'z')
                {
                    letter = (char)(letter - 26);
                }
                else if (letter < 'a')
                {
                    letter = (char)(letter + 26);
                }
                buffer[i] = letter;
                s++;
                if (s == shiftLength)
                    s = 0;
            }
            return (Encode ? key : "") + new string(buffer);
        }