WAD Challenge

N.B.

For the solutions refer to https://github.com/marmos91/wad

Assignement

Well done! If you are here it means you have passed stage 0 of the challenge. NOTE: If you have landed here before completing stage 0, please go back to http://wad-challenge.s3-website.eu-central-1.amazonaws.com/. You will need some info contained there...

Introduction

The goal of the challenge is decrypt the following text:

&22.UJJ W$!U!MU "#UNOUO MUR|YUN KNKJ5', ,#0

Decrypting it you will access the final stage of the challenge and light up the IoT device.

You can use any programming language to complete this stage.

The algorithm

The algorithm used to encyrpt the message was a block cipher with the following rules:

The alphabet is restricted between ascii codes 33 ("!") and 125 ("}") included. If you are not familiar with ASCII give a look at http://www.asciitable.com/ and https://en.wikipedia.org/wiki/ASCII
The algorithm encryption and decryption processes expect a key in the form of a string and a message (also a string). In pseudocode:

string encrypt(string key, string message)
{
    // body
}

string decrypt(string key, string message)
{
    // body
}

Some examples

titanic -> 2'2|,'!
minecraft -> +',#!0| $2
javascript -> (|4|1!0 '.2

Here are the encryption steps:

The message is split in chunks of length key.size
Each chunk is reversed (eg. asdfg --> gfdsa)
For each chunk:
- Each character is shifted upwards by n positions where n is the sum of the ASCII decimal codes of the encryption key
- If the selected code exceeds the alphabet's length it must be reassigned from the alphabet start (e.g using the modulo operator 🤓)
After the operation each chunk has to be reversed back again
Every key.size chunks, a new line is added in the output

The given encrypted message was generated following the above steps. Now it is your time to write the decryption algorithm to reverse the process!

And then?

The decoded message will contain an URL. You will have to perform an HTTP request to the URL with the following informations:

A code: this will be the encryption key itself encrypted with the algorithm above (so you have to also implement the encryption part to succeed).
Your name: it will be displayed on the LCD of the challenge's device.

Something missing?

Do you still need the encryption/decryption key? Have you deeply inspected the first stage's code? 🤓

Bad news: that was not all...

Also review the arp protocol. Do some research on the network on how to obtain an IP address from a physical Mac Address. Trust me, you will find it useful 😉 Also, do you know how to make an HTTP request right?

Questions?

Feel free to ask any question, but do not expect always an answer 😉

marmos91/wad-challenge