You’re almost done with this, try harder! Once you have all the needed information from previous step, go have a look here (https://gcorp-stage-4.ctf.insecurity-insa.fr/) Note: you should validate stage 3 to have more information on stage 4.
As crypto expert we designed our own streamcipher that combines two linear elements into a secure design. It works as follows. The secret key of NONSENSE consists of two invertible matrices K 51 , K 52 ∈ Z 64×64 To encrypt a plaintext M of l bits, our algorithm takes a 64-bit IV, generates an l-bit key stream k and computes the ciphertext C = M ⊕ k. The keystream is generated in 64-bit blocks as implemented in our open source file. To enforce a bit more the security, we decided to include IV into the secret key as well, it is incremented after every encryption query by 1, i.e. IV = (int(IV) + 1 mod 2^64 i) with limited 64 bits. You can find attached our implementation and here is our incrackable test : BXkOb8rYcnNpR3db/Ly5cD+EyBJnm8sorjHZTx/yAhUi
You did a very good job until now. To be sure no one is going to be trapped again, could you find a way to protect the whole company?
To do so, you can use the binary located on the website of part 2, our expert told us that is was safe to run.
Note: you need to solve part 2 before attempting this part
Edit: Microsoft flagged the old binary as a malware, please redownload the new version (the old version won’t give you the correct flag)
All you need to do is to
pwnusing some DNA samples…
Once you gathered enough information, go checkout this
Note: you should validate stage 1 to have more information on stage 2.
I’ve just written a small utility to create a config file (which are sooo painful to write by hand, right?).
Care to have a look?
nc config-creator.ctf.insecurity-insa.fr 10000