Sharif University CTF Quals 2014

In these tasks we were given a service which:

• accepts .cpp file
• compiles it via MSVS10 or gcc4.8 (you can choose which one)
• launches a couple of tests on successfully compiled binary

You can look at it here, here and here.

[To try to solve the task see an attachment below the writeup]

For this particular task we've been given some sort of CA to issue user certificates and authentication part to verify issued user certificate using SSL handshake. The main purpose according to the message provided after authentication is to login with certificate issued to the user named admin. There is no sense telling that one can not do this in ordinary way by requesting it from CA provided.

This time we are given a rather long file, presumably ciphertext -- the result of AES transformation weak in some sort of way. After taking a look at it in Sublime we can't find anything wrong with it: indeed, Sublime does normally hang after us trying to make a full-text search through the file. Let's better make it binary and open in some lightweight hex editor.

Task:

Decrypt the message!

And 'ecnrypted.txt' is attached to task:

Task:

flag="*********"
def RabinKarpRollingHash( str, a, n ):
        result = 0
        l = len(str)
        for i in range(0, l):
                result += ord(str[i]) * a ** (l - i - 1) % n
        print "result = ", result


RabinKarpRollingHash(flag, 256, 10**30)

output is 
1317748575983887541099 
What is the flag?

Solution:

This is most common task where we have two images with black and white pixels and need to XOR them pixel by pixel. Let the white pixel be 1 and black pixel be 0. Further description is not needed. Code is attached. Flag is AZADI TOWER.

There we got a dump of UDP packets in pcap file.