Decodex User Guide

Table of Contents

• Introduction
• Terminologies
• Symbols
• Quick Start
• List of Available Modules
• Features
  • Basic Commands
    • Help: help
    • Input of Data: input
    • List Available Modules or Recipes: list
    • Select a Module or Recipe: select
    • Show Current Data: show
    • Reset Data: reset
    • Exit the Program: exit
  • Recipe Commands: recipe
    • Create a New Recipe: recipe new
    • Select a Recipe for Editing: recipe select
    • Deselect the Current Editing Recipe: recipe deselect
    • List Modules in a Recipe: recipe list
    • Add a Module to a Recipe: recipe push
    • Remove a Module from a Recipe: recipe pop
    • Clear All Modules in a Recipe: recipe reset
    • Delete a Recipe: recipe delete
  • Storage of Recipe Files
    • Load Recipe Files on Startup
    • Save Recipe to File
    • Delete Recipe File
  • Reading/Writing Data from/to File coming soon in the future
• Command Summary
• FAQ

Introduction

Decodex is a Command Line Interface (CLI) application for Capture-The-Flag (CTF) players to perform encoding, decoding, encryption and decryption of data, which come in the form of modules that can be executed with ease and without any programming needed. Decodex also provides recipes which can also be used to link several of these modules together so that they could be executed in one go to speed up repetitive tasks. The intuitive interaction can thus help to speed up a player’s performance during CTFs and save time without having to manually code the tedious data transformations.

This guide serves to help you understand the usage of the program, which includes performing data transformations using basic commands as well as developing and managing recipes using recipe commands.

This user guide is tailor-made for CTF players who have some technical understanding of encoding schemes and cryptography.

Terminologies

This section serves to help you better understand the terminologies used in this user guide.

Terminology	Definition
Data transformation	The conversion of one data format to another.
Application, Program	Refers to the Decodex program. These two terms are used interchangeably in this User Guide.
Encoding	Converting a message into a coded form.
Decoding	Converting a coded message into an intelligible form.
Encryption	Converting a message into a form where only authorized parties are able to decipher it.
Decryption	Converting an encrypted message back to its original form by deciphering it.
Base64, Binary, Hexadecimal	Common types of data encoding standards.
Console	This refers to your command prompt window.
Argument	Additional information that you provide to the program’s command.
Module	A self-contained set of instructions to process your data into another form. A full list of supported modules can be found here.
Recipe	Acts as a container for you to link several modules together that will be executed back-to-back on your data. By default, the application does not have any default recipes installed.

Symbols

Symbol	Definition
	Represents a good tip for you.
	Represents something important that you should take note of.
	Represents additional information regarding commands/features for you to better understand how to use it.
	Represents something optional that you can try out, mostly for exploring or fun.

Quick Start

1. Ensure you have Java version 11 or above installed on your computer.
   1. If you haven’t, you may download it here.

      You should download the installation relative to your Operating System.

2. Next, download the latest decodex.jar here.
   1. Simply click on decodex.jar under “Assets” and the download should start.
3. After downloading, you can open up command prompt.

   To open command prompt, press win + r at the same time, then type and enter cmd.

4. Afterwards, you can run decodex.jar by typing in java -jar decodex.jar and Decodex’s prompt should appear. Please also ensure that you are in the same directory as where you have downloaded decodex.jar.
   1. In the screenshot below, you can see that decodex.jar is run in the Downloads folder. To add on, it also shows you how to better understand the startup prompt of Decodex.
5. Now, you are ready to try out some of the basic commands below:
   1. input I am groot: Inputs the text data I am groot into the program.
   2. list: Lists all available modules and recipes that you can use.
   3. select module base64encode: Selects and runs the base64-encoding module on the data.
   4. reset: Resets the changes made to data - resetting to its original data.
   5. exit: Exits the application.
6. For more information on Decodex’s features, please refer to the Features Section.

To make things more interesting while learning how to use Decodex, you may try to find out what NTEgMzEgNTIgNDcgNjUgMzAgNGUgNTQgNGQgNmEgNDUgNzggNGQgMzEgNTIgMzk= using our application! If you are new here, you can continue reading this guide to understand how to unravel this mysterious text!

List of Available Modules

Below, you can see the list of available modules and what they do.

These are some of the more common encoding/decoding/cipher methods that can be found in CTF competitions.

Module	Description	moduleArgument
base64encode	Encodes the data using base64 format.	N.A
base64decode	Decodes the data using base64 format.	N.A
hexencode	Converts the input string to hexadecimal bytes.	N.A
hexdecode	Converts a hexadecimal string back into its raw value. Note that this module does not accept any form of separators (space, commas, etc.) in the data.	N.A
binencode	Encodes the data using binary format.	N.A
bindecode	Decodes the data using binary format. Note that this module does not accept any form of separators (space, commas, etc.) in the data.	N.A
rotencode	Rotates alphabetical characters by a specified integer offset. E.g., select module rotencode 13, recipe push rotencode 13	The rotation offset. Must be an integer between -2,147,483,648 (MIN_INT) and 2,147,483,647 (MAX_INT).

Features

Notes about the commands and arguments:

• Arguments enclosed in <> are mandatory arguments while arguments enclosed in {} are optional arguments. For example, select <moduleName> {moduleArgument} would mean that moduleName is mandatory while moduleArgument is optional.
• Arguments must be entered in the exact order and position as specified in the commands’ respective formats.
• All commands and arguments are case-sensitive.
• After the execution of a command, you may see a [+] , which means that it ran successfully or a [x], which denotes that an error has occurred.

Basic Commands

Help: help

Lists the syntax and descriptions of all available commands.

Format: help

Example:

Input of Data: input

Stores the data to be processed by modules.

Format: input <data>

data will be treated as text.

Examples:

• input HelloWorld! Enters the plain-text HelloWorld! as data.
• input SGVsbG9Xb3JsZA== Enters the base64-encoded text SGVsbG9Xb3JsZA== as data.

Behaviour of the input command:

• Note that the program will consider all characters as data following the first space character in the input command. You may observe leading and trailing whitespaces in the output.
• Non-printable characters (e.g. null characters) may not be correctly displayed and could potentially scramble the user interface.

List Available Modules or Recipes: list

Shows a list of all available modules or recipes.

Format: list {category}

Notes about the list command:

• The acceptable values of category are modules and recipes .
• When category is not specified, both lists of modules and recipes are printed.

Examples:

• list Lists all available modules and recipes.
• list modules Lists available modules only.
• list recipes Lists available recipes only.

Select a Module or Recipe: select

Selects a module or recipe and processes the data accordingly. Subsequent selection of modules or recipes will process the transformed data output from the previous module or recipe.

Format: select module <moduleName> {moduleArgument}, select recipe <recipeName>

Notes about the select command:

• moduleName is the name of an available module supported by Decodex. moduleArgument is an argument that certain modules accept as input.
• recipeName is the name of an available recipe that is loaded by the program.
• You may also refer here for more details on our modules and its usage.

Examples:

• select module base64decode Runs the base64decode module on the current data.
• select module rotencode 13 Runs the rotencode module with argument 13 on the current data.
• select recipe testRecipe1 Runs the testRecipe1 recipe on the current data.

Show Current Data: show

Shows you the current data.

Format: show

Reset Data: reset

Resets the transformed data back to the original input.

Format: reset

Exit the Program: exit

Exits the program.

Format: exit

If you are trying out the side-quest from earlier and can’t seem to find the solution to it, you may refer to the solution in the picture at the start of the user guide!

Recipe Commands: recipe

During the execution of the application, it would display the name of the recipe that is “currently being edited” (if any) in [] of the application’s prompt. This currently edited recipe will be the target for some recipe commands such as recipe push, recipe pop and recipe reset.

Create a New Recipe: recipe new

Creates a new recipe and sets it as currently being edited.

Format: recipe new <recipeName>

recipeName can only contain alphabets, numbers and underscores.

Example:

• recipe new testRecipe Creates a new recipe with the name testRecipe.

Select a Recipe for Editing: recipe select

Sets a recipe as currently being edited.

Format: recipe select <recipeName>

Example:

• recipe select testRecipe Selects testRecipe as the recipe to be edited.

Deselect the Current Editing Recipe: recipe deselect

Deselects the recipe currently being edited.

Format: recipe deselect

Example:

List Modules in a Recipe: recipe list

Show all the modules in a recipe, in the order they were added.

Format: recipe list {recipeName}

When recipeName is not specified, modules from the recipe that is currently being edited will be listed instead.

Example:

• recipe list testRecipe Lists the modules in the recipe named testRecipe.

Add a Module into a Recipe: recipe push

Adds a module into the recipe that is currently being edited.

Format: recipe push <moduleName> {moduleArgument}

Example:

• recipe push base64encode Adds the base64encode module into the current editing recipe.
• recipe push rotencode 13 Adds the rotencode module with a single argument 13 into the current editing recipe.

Remove a Module from a Recipe: recipe pop

Removes the most recently added module from the recipe that is currently being edited.

Format: recipe pop

Clear All Modules in a Recipe: recipe reset

Removes all modules from the recipe that is currently being edited.

Format: recipe reset

Delete a Recipe: recipe delete

Deletes a recipe from the program.

Format: recipe delete <recipeName>

Example:

• recipe delete testRecipe Deletes the recipe with the name testRecipe.

Storage of Recipe Files

Notes about the recipe files

• A recipe will correspond to a recipe file which is a plaintext file with the name <recipeName>.txt where recipeName is the name of the recipe.
• It is highly recommended that you only modify recipe files through the recipe commands in Decodex and not manually edit the recipe files.
• If you choose to manually edit the recipe files, the correct format would be that each line in the respective recipe file should contain only one module, and they should be formatted in the following syntax of <moduleName> {moduleArgument}. You should also not be editing while Decodex is running as Decodex could accidentally overwrite your changes.
• Incorrectly edited files will be considered as invalid and will not be loaded on program start up.
• The recipe files would also not be loaded successfully if Decodex does not have access rights to the files, or it is not in the valid filetype.

Load Recipe Files on Startup

Loads the recipes from the recipe files found in the recipe/ directory. This is done automatically for you on startup so that you do not have to manually add multiple recipe files into Decodex each time.

Save Recipe to File

Saves the recipe to a recipe file in the recipe/ directory. This is done automatically for you whenever a recipe is created or modified so that it is more convenient and less punishing for you (especially if you often forget to save your documents before exiting).

Delete Recipe File

Deletes the recipe file in the recipe/ directory. This is also done automatically for you (via the recipe delete command), so that you do not have to manually find the corresponding recipe file to delete it.

Reading/Writing Data from/to File [coming soon in the future]

Coming soon to a cinema near you in the future…

Command Summary

Action	Command Format	Example Usage
View the syntax and description of commands	help	help
Enter input data	input <data>	input HelloWorld!
List available modules/recipe	list {category}	list list modules list recipes
Select processing module/recipe	select module <moduleName> {moduleArgument}  OR select recipe <recipeName>	select module base64decode select module rotencode 13 select recipe testRecipe1
View current data	show	show
Reset to original data	reset	reset
Create new recipe	recipe new <recipeName>	recipe new testRecipe
Select recipe for editing	recipe select <recipeName>	recipe select testRecipe
Deselects the recipe currently being edited	recipe deselect	recipe deselect
List modules in recipe	recipe list {recipeName}	recipe list testRecipe
Add module to recipe	recipe push <moduleName> {moduleArgument}	recipe push base64encode recipe push rotencode 13
Remove module from recipe	recipe pop	recipe pop
Clear all modules in recipe	recipe reset	recipe reset
Delete recipe	recipe delete <recipeName>	recipe delete testRecipe
Exit program	exit	exit

FAQ

Q: How do I transfer my recipes to another computer?
A: Install the app on the other computer and copy the recipe files from the computer that you are transferring from, into the recipe folder of the computer that you are transferring to.