Description
Download this file and find the flag.
Solution
After unziping this file we found that it's x64 ELF. At the main function we see some buffer dexoring:
Lets dexor it and save to file (IDA command line with idapython used):
Task:
Connect here and find the flag:
`nc asis-ctf.ir 12435`
Solution:
This kind of famous task. You have board with buttons, wich have 2 positions. In Russia there is old quest game with brother pilots and there was the same task to open the fridge with board 4x4. And there was solution remember all buttons in first position. And switch all this buttons one by one. Repeating this algoritm from 1 to 3 times, you will win.
As we can see from the task, the talk is about DNA replication, as said my friends from team, we should find the most popular string in the given file.
First of all, I should say, that I'm using python. In the start I just tried to build index where keys are string that can be found in file and values are there frequency. But that didn't work. Because in python index always saved in the RAM, and for my counting, I should have more than 16GB (I think something like 32 or 64). That numbers is reachable, but I guessed that it should be better solution.
Task:
Universal dangerous positive: 194.226.244.125:1024. Send me your password: "3k8bbz032mrap75c8iz8tmi7f4ou00". Flag format is "RUCTF_.*"
Задание:
Мое внимание привлекает монитор. На него наклеен стикер с надписью B4365F2. Видимо, это какой-то ключ. На экране мигают две точки, соединенные пунктиром, а ниже бегут пакеты сетевого трафика. Наверное, это передача каких-то команд ракете. Но, по всей видимости, передаваемые данные зашифрованы... На компьютере также открыт файл, в котором записаны два IP-адреса (213.170.102.196:4001, 213.170.102.197:4002). Наверняка IP-адреса помогут мне понять схему работы протокола, по которому передаются команды! Да и в отладочной информации, если покопаться, можно будет обнаружить что-нибудь полезное...
First we see the text on the page: "You must specify a nick". After quick look into source code of the page we understand that our URL must contain GET-parameter 'nick' with random value.
Then server sends us some leet-modified string like
51xty tw0 plu5 0n3
and expecting from us solution of this expression in the same format.
Experimentally found that there is only 4 leet-modified characters: '1' == 'i', '3' == 'e', '5' == 's', '0' == 'o'.
The name of this task connected to "Markov chain"
The main idea of that system is that the next state depends only on the current state, and there is a probability of transition.
First try shows, that one word phrases are shutting down the connection.
So we need to start with two word phrase. First hint is in the password:"talk_with_markov_about_positive_things".
