I have one question about convergent encryption.
Suppose I use AES-256 in CBC mode. I need a 256 bits key and a 128 bits IV. If I use SHA-256 to hash one file, then I can use directly that hash as the key.
When decryption occurs, is integrity and authenticity given by checking the hash of the decrypted plaintext, OR is there a need to add additionnals integrity and authenticity checks like CBC-MAC ?