Scripting for CTFs - A New Tutorial Series

In the interest of developing and improving the scripting skills useful for Capture the Flag competitions of beginners who are not exactly new to programming but have no idea how to start doing the On-the-Fly hacks required, the Nandy Narwhals have decided to begin writing a series of tutorials to address this need. This is especially directed at students of the Dip. in Infocomm Security Management Course at Singapore Polytechnic who learn the basics of programming basic applications but run into difficulties dealing with solving problems requiring quick and dirty tricks favouring speed over robust design.

Now, our usual approach to teaching these students our methodology in tackling CTF challenges involves forcing them to learn a language we prefer over one they already know (i.e. Python) before actually getting into the gritty and useful content. So, we’ve decided to swap out this approach for something that might work better: introducing an objective (such as “opening a TCP socket and receiving data”) at the high level and then demonstrating the implementation in multiple languages such as Java and C which should be more familiar to DISM students to make making the connection easier.

To benefit from these tutorials, we recommend that you are familiar with at least one of the languages. Do note that we will be primarily using Python 2, unless otherwise stated.

Let’s demonstrate this.

Hello World!

A simple Hello, World! program done in Python, Java, C, Perl, and Ruby. Output should look something like this:

$ python helloworld.py
Hello, World!

Python

print("Hello, World!")

Java

public class HelloWorld {
    public static void main(String[] args) {
        System.out.println("Hello, World!");
    }
}

Perl

use strict;
use warnings;

print "Hello, World!\n";

C

#include <stdio.h>

int main()
{
    printf("Hello, World!\n");
}

Ruby

puts 'Hello, World!'