//@nuget: Microsoft.VisualBasic -Version 10.0.0

using System;

using Microsoft.VisualBasic;

using Microsoft.VisualBasic.CompilerServices;

​

public class Program

{

    public static string Crypt(ref string Action, ref string Key, ref string Src)

    {

        string text = "";

        checked

        {

            short num = (short)Strings.Len(Key);

            short num6 = default(short);

            if (Operators.CompareString(Action, "E", TextCompare: false) == 0)

            {

                short num2 = 91;

                text = Conversion.Hex(num2);

                short num3 = (short)Strings.Len(Src);

                for (short num4 = 1; num4 <= num3; num4 = (short)unchecked(num4 + 1))

                {

                    short num5 = (short)unchecked(checked(Strings.Asc(Strings.Mid(Src, num4, 1)) + num2) % 255);

                    unchecked

                    {

                        num6 = (short)((num6 >= num) ? 1 : checked((short)(num6 + 1)));

                    }

​

                    num5 = (short)(num5 ^ Strings.Asc(Strings.Mid(Key, num6, 1)));

                    text += Strings.Mid(Conversion.Hex(num5), 1, 2);

                    num2 = num5;

                }

            }

            else if (Operators.CompareString(Action, "D", TextCompare: false) == 0)

            {

                short num2 = (short)Math.Round(Conversion.Val("&H" + Strings.Left(Src, 2)));

                short num7 = (short)Strings.Len(Src);

                for (short num4 = 3; num4 <= num7; num4 = (short)unchecked(num4 + 2))

                {

                    short num5 = (short)Math.Round(Conversion.Val("&H" + Strings.Trim(Strings.Mid(Src, num4, 2))));

                    unchecked

                    {

                        num6 = (short)((num6 >= num) ? 1 : checked((short)(num6 + 1)));

                        object obj = num5 ^ Strings.Asc(Strings.Mid(Key, num6, 1));

                        obj = ((!Operators.ConditionalCompareObjectLessEqual(obj, num2, TextCompare: false)) ? Operators.SubtractObject(obj, num2) : Operators.SubtractObject(Operators.AddObject(255, obj), num2));

                        text += Conversions.ToString(Strings.Chr(Conversions.ToInteger(obj)));

                        num2 = num5;

                    }

                }

            }

​

            return text;

        }

    }

​

    public static void Main()

    {

        Console.WriteLine("Hello World");

        string Action = "D";

        string Key = "ROBERTFKAISER";

        string Src = "5B99B56B9B41E4113E1E76C4";

        Console.WriteLine(Crypt(ref Action, ref Key, ref Src));

    }

}