I need help for a "simple" problem
Let's suppose an intercepted ciphertext C encrypted with an AES-CFB mode of operation, using key K and some IV (IV is probably at the begining of C)
The system let us access to a black box encrypting any tupple (plaintext, IV) using AES-CTR mode with the same key K.
I succeed compute the keystream of the CTR mode using output of the black box, but I still need the keystream of the CFB mode before decrypting C.
Anyone has an idea how to do it ? Thanks