Suppose I want to encrypt some plaintext and I can only use an unauthenticated AES mode like CBC.
One way of adding authentication is encrypt-then-MAC, where the two different keys for AES and MAC are derived from the same passphrase using a key derivation function.
Is the above more secure than encrypting the plaintext along with its hash? When decrypting, the hash is then separated from the plaintext and verified. So if the ciphertext is tampered with, the hash verification has to fail (as long as a proper cryptographic hash is used).