The overall setup is that I am using RSA public key encryption, and because the messages are big instead of encrypting the entire message via RSA I am encrypting a random AES-128 key with the PK and then encrypting the message with that in AES-CBC.
The AES key is randomly generated for each message. Questions:
Is it safe to use the key as the IV of the CBC? The rationale here is the key is unique and random for each message and I'm not seeing a problem. The key is used in 3 places thus: the encryption itself, then as an IV, then again concatenated with the encrypted message's hash and everything hashed again as a MAC.
Do I still need to do any random padding on the IM itself? The key and IV are already unique and random.