I was trying to do a simple CPA attack against this scheme, to understand better the concept.
Instead of using a new 𝐼𝑉 each time, we decide to use the last block of the previous ciphertext as an initialization vector. Prove this new scheme is vulnerable to a chosen-plaintext attack.
So in this case,
- the challenger chooses a "game" and a key.
- After that, we send $(0\ldots 0,1\ldots 1)$
- and we receive $(IV, c)$.
- Now we send $(0\ldots 0, 0\ldots 0)$
- and we receive $(IV'=c , c')$.
- So if $c$ is equal to $IV'$ then the challenger is playing the left game, right otherwise.
Am I right? Am I confusing the concepts? When we talk about a block, is all the cipher or only the last bit?