# A Weird List of Sequences (Misc)

Hi CTF player. If you have any questions about the writeup or challenge.
Submit a issue and I will try to help you understand.

Also I might be wrong on some things. Enjoy :)

(P.S Check out my [CTF cheat sheet](https://github.com/flawwan/CTF-Candy))

![alt text](1.png "Chall")

Connecting to the netcat server we get a prompt saying we need to supply a
captcha code.

![alt text](2.png "Chall")

Using pwntools and a simple md5 bruteforce script we quickly crack the
captcha.

Script available here: [brute.py](brute.py)

After cracking the captcha, we can start the challenge.

![alt text](3.png "Chall")

Okay we have to predict the number sequence 25 times. Doing it by hand is
quite hard. Let's use `oeis.org`.

![alt text](4.png "Chall")

Again manually typing all these numbers in to the website is boring. Also
there might be a timeout (untested). Automating the process with python is
easier and more fun. Let's do that.

### Creating a automatic tool to solve the task

Our goal is to:  
* Bruteforce the captcha  
* Parse the given number sequence.  
* Send the number sequence to oeis.org.  
* Fetch the next predicted number from the response of oeis.org.  
* Send the number to the server.  
* Loop 25 times.  
* Get the flag

With this python script I used the following libraries:  
* Pwntools - Connect to challenge server over tcp.  
* requests - To send GET request to oeis.org  
* pyquery - Parsing the response of oeis.org to get the next predicted number  
* hashlib - md5 encode function

Full script available here: [solve.py](solve.py)

Running the script, we get the flag after 25 solved sequences! Cool

![alt text](5.png "Chall")  

Original writeup (https://github.com/flawwan/CTF-
Writeups/blob/master/XMAS2018/A%20Weird%20List%20of%20Sequences/writeup.md).# A Weird List of Sequences (Misc)

Hi CTF player. If you have any questions about the writeup or challenge.
Submit a issue and I will try to help you understand.

Also I might be wrong on some things. Enjoy :)

(P.S Check out my [CTF cheat sheet](https://github.com/flawwan/CTF-Candy))

![alt text](1.png "Chall")

Connecting to the netcat server we get a prompt saying we need to supply a
captcha code.

![alt text](2.png "Chall")

Using pwntools and a simple md5 bruteforce script we quickly crack the
captcha.

Script available here: [brute.py](brute.py)

After cracking the captcha, we can start the challenge.

![alt text](3.png "Chall")

Okay we have to predict the number sequence 25 times. Doing it by hand is
quite hard. Let's use `oeis.org`.

![alt text](4.png "Chall")

Again manually typing all these numbers in to the website is boring. Also
there might be a timeout (untested). Automating the process with python is
easier and more fun. Let's do that.

### Creating a automatic tool to solve the task

Our goal is to:  
* Bruteforce the captcha  
* Parse the given number sequence.  
* Send the number sequence to oeis.org.  
* Fetch the next predicted number from the response of oeis.org.  
* Send the number to the server.  
* Loop 25 times.  
* Get the flag

With this python script I used the following libraries:  
* Pwntools - Connect to challenge server over tcp.  
* requests - To send GET request to oeis.org  
* pyquery - Parsing the response of oeis.org to get the next predicted number  
* hashlib - md5 encode function

Full script available here: [solve.py](solve.py)

Running the script, we get the flag after 25 solved sequences! Cool

![alt text](5.png "Chall")  

Original writeup (https://github.com/flawwan/CTF-
Writeups/blob/master/XMAS2018/A%20Weird%20List%20of%20Sequences/writeup.md).