Aham....

aham.cs

/// <summary>
        /// </summary>
        public static string Cypher(string input)
        {
            StringBuilder result = new StringBuilder();
            Regex regex = new Regex("[A-Za-z]" );

            foreach (char c in input)
            {
                if (regex.IsMatch(c.ToString ()))
                {
                    int charCode = ((c & 223) - 52) % 26 + (c & 32) + 65;
                    result.Append((char) charCode);
                }
                else
                {
                    result.Append(c );
                }
            }

            return result.ToString();
        }