# Is it possible to narrow down the possible keys used for AES CBC encryption, knowing a given plaintext and its ciphertext, where IV=0? [duplicate]

I'm brute forcing a ciphertext with a given dictionary to figure out which key was used. However, it's been hinted at that there is a way to narrow down the dictionary to a smaller subset of possibilities.

I know the plaintext, its ciphertext, and the IV (0). It was encrypted using AES-128-CBC and no salting was used during encryption.

At first I thought I was onto something because of: $$C_j = E_k(P_j \oplus IV)=E_k(P_j)$$ for IV = 0. But I was dead in my tracks right after. Is this situation even plausible or am I barking up the wrong tree?