Hi I'm trying to understand the logic behind a CTF challenge basically we are given a program which encrypt some data, we have the following options:
- Select encryption mode (EBC, CBC, CTR, OFB, CFB)
- Encrypt the flag and see the resulting ciphertext
- Encrypt a choosen plaintext and see the resulting ciphertext
Now I think the weakest alg here is ECB, but bruteforce block of 128 bits seems not feasible at all to me.
Each time a plaintext is encrypted a new random IV is used (when needed so for CBC, CBF and OFB).
Which could be a good strategy to attach such program? My objective is finding the plaintext for the flag.