prove that the chained CBC mode of encryption of block cipher is not CPA-secure.

(Hint: using CPA indistringuishability experiment, to distinguish which messages was encryption, allow the adversary to select its encryption queries, and then select the challenge messages, (m0, m1), based on the response for the encryption queries (m', c0).)

Assume in training phase, adversary queries the encryption oracle with message m', and get ciphertext c0=Fk(IV XOR m'). Attacker (you) needs to choose a pair of message (m0, m1), and one of the messages will be randomly selected and encrypted (mb, b=0 or 1 randomly), and let ciphertext be c1. You need to choose one plaintext, say m0, and it is distinguishable, or you can distinguish which message was encrypted.