Would this encryption and signing scenario be considered tamper-proof?
plaintext = "hello world" password = "secret key" hash = sha3_512(plaintext) ciphertext = encrypt(plaintext,password) output = ciphertext+hash
I'm computing the hash of the plaintext and then adding it to the end of the ciphertext output. I know this isn't exactly MAC or HMAC, but does this scenario work? Is it secure? From my perspective, the only way to forge the plaintext is if you know the key. Otherwise, any change will be reflected in the hash. Is this secure? Assume that the cipher is non-malleable. I believe this is the scheme used by Mcrypt for file encryption. Thanks.
This is not a duplicate because it would be infeasible to brute-force the plaintext from the hash as described in the possible duplicate question, scenario 3.