Symmetry

An embarrassing challenge for me. The solution to this challenge is quite simple. The symmetry of the xor operation enables us to decrypt the message/plaintext $P$ from the $IV$ and ciphertext $C$. Denote the output after running block cipher encryption with key k $E_k$ to be $O$, then we have: $$O = E_k(IV)$$ $$C = P \oplus O$$ xor both sides of the above equation, we have:...