toby toby-bro

Chrono rage

In this challenge we are given two files,

a pcap dump of the traffic between the attacker and the server,
the server's implementation

Analysis of the script

Le Calme Avant La Tempest

Avertissement

Je me doutais que ce challenge pouvait être résolu avec TempestSDR mais je ne trouvais pas ça assez intéressant d'essayer de comprendre le projet et me suis mis en tête de faire cette extraction par moi-même.

Le code que je présente est probablement pas super optimal, je l'ai écrit pendant le CTF et la seule modification que je me suis permis d'y apporter est de séparer en plusieurs fichiers pour plus de lisibilité et vous éviter la lecture d'un fichier de 1694 lignes.

Canflag

Link to the challenge

We are given a pcap of a CAN bus that does not have too many different packets. When reading the packets we see that some seem to have text in them, in their data field. We also see a few packets that interest us:

the one which has 'FCSC' has id 2 and is an extended packet
the one which has '{' has id 2 and is not an extended packet

Au boolot

Link to the challenge

Understanding the problem

We have an oracle to the output of a logic circuit only composed of XORs. The circuit takes in input a 128 bit value, and returns a 256 bit output value.

We can send upto 130 different input values to the oracle before he asks us to guess the output of another value.

This challenge's instructions were fairly straightforward and the principal difficulty I met in its resolution was not botching the implementation of Gold and LFSR... which I did many times. Resigned I went on github cloned a repo: chrinels/sequences that did it flawlessly and now things were going.

Once this was done the script basically just :

reads the audio file
enumerated the different phases specified in the instructions, and for each of them
- calculated the correlation between the Gold code step and the audio data
- determined for each bit if the data were positively correlated then the bit was 1 else 0
- translated the binary to ASCII
enjoyed

File format

Naïve bash

To solve this challenge I started with a pure bash approach. The original file is i_0 q_0 i_1 q_1 ... So i start by separating each i_k q_k on a separate line

xxd -c 8 -g 4 -p file-format.iq

Un cercle est un carré

Lien vers le challenge

Ce problème a été de loin celui qui m'a le plus fait m'arracher des cheveux lors de ce FCSC.

Je passerai les détails mais après avoir passé plus d'une journée à faire des projections de segments sur des plans diagonaux puis sur des arrêtes pour refaire une sorte de projection cubique à la manière d'une projection sphérique du segment $[P, Q]$ et avoir vu que c'était pas la solution exacte mais une bonne approximation... J'ai enragé et j'ai cherché sur internet et je suis tombé sur

	#!/bin/bash

	# Print the table header
	echo -e '╭─────────────────┬────────────────────╮'
	echo -e '│ Interface │ IP Address │'
	echo -e '├─────────────────┼────────────────────┤'

	# Get the list of network interfaces and their IP addresses
	ip -brief address \| awk '{
	printf "│ %-15s │ %-18s │\n", $1, $3

	#!/bin/bash

	# Print the table header
	echo -e '╭─────────────────┬───────────────────────────┬─────────────────────┬──────┬──────┬──────╮'
	echo -e '│ Process │ Local Address │ Foreign Address │ Prot │ RcvQ │ SndQ │'
	echo -e '├─────────────────┼───────────────────────────┼─────────────────────┼──────┼──────┼──────┤'

	# Get the output of ss and process it
	sudo ss -lntup \| awk '
	function truncate(str, max_len) {

	#!/bin/bash
	TEAM=00001 #REPLACE WITH THE TEAM NUMBER THAT INTERESTS YOU
	table=$(curl -s https://ctftime.org/team/${TEAM} \| grep -P '<div class="tab-pane active" id="rating_202\d"' -A 999 \| grep -P '<div class="tab-pane" id="rating_202\d"' -B 999 \| grep -P '<tr><td class="place_ico"></td><td class="place">\d+</td><td><a href="/event/\d+">[\s\w\d]+</a></td><td>[\d\.]+</td><td>[\d\.]+</td></tr>'); for i in $(echo $table \| grep -Po '(?<=<td>)[\d\.]+(?=</td></tr>)' \| sort -h \| tail -n 10) ; do echo -n "$i -- "; echo $table \| grep $i \| grep -Po '(?<=<a href="/event/\d{4}">)[\w\s\d]+(?=</a>)' ; done