ECB is considered to be insecure when used for confidentiality because identical plaintext result with identical ciphertext. But what if we use ECB for authentication?
Assume A wants to transmit an authenticated message X to B. A and B have a shared key. What if A encrypts the plaintext X using AES-ECB and outputs Y as the ciphertext and appends it next to the plaintext X as a MAC? Would that be secure?
Confidentiality is not of importance here. We only need to authenticate the data.