fine fine fine i got that solved that issue. successfully started the server.
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For anyone trying to solve this challenge and not knowing what the ■■■■ is going on, I highly recommend going over to the Matasano cryptographic challenges (also know as Cryptopals). It’s a lot of work but it pays off 
That being said, if you know what attack to use it’s not necessary to dive into the concepts.
Hi guys, need help… don’t know how to proceed further after starting the app.py script
Hello, I have some problems when sending bytes belonging to a crafted ciphertext: since it’s an encrypted string, many bytes are not even printable and the decode() in the app.py gives me an error saying it cannot decode that specific bytes. But how am I supposed to send a ciphertext as required if it refuses those bytes?
Also, I receive many errors like “must be str, not bytes” or “odd length string” even when these conditions aren’t real ahahah, meaning that my payload is actually an odd length string.
EDIT: Solved, many of my problems were caused by not using hexlify/unhexlify functions, as used by the source, so make good use of them
As suggested by others as well, the name of the challenge is a big hint for the kind of attack that can be performed here, so get on Google and start learning.
Hi can someone help me?
I know how the attack works. But i won’t be able to do a script in to get the right answer. Can u give me some tips?
Im trying with python3.
I had trouble with socket. But now it works. Thanks!
i can’t run app.py locally it keeps giving this error
return enc.hex() AttributeError: 'str' object has no attribute 'hex'
Hello I am new to HTB, I understand that I can download the files and create my own secret.py and solve the challenge that way. But how do I find the flag that we are suppose to submit in the challenge. What does the start instance in the challenge do? I need tutorial.
Edit : Figured out how to connect to the instance using netcat lol!
After I saw your hint I gone for like every single link in google’s first page of the f exploit 
The crypto it uses is hard to understand with all those formulas and values, but trying different things and encoding/decoding with your own bytes can prove useful
Maybe I will try it again in some time to make sure I really understood the blocks, but now i need so much to sleep
For anyone new in 2023 trying this challenge, R is here to help 