[bwackwat]

Ok so I guess the resulting lesson from Canada for me is that having a HASH or MAC for encrypted files is the most critical part of any secure system OP is interested in.

Furthermore, Canada, what about privately managed machines communicating via TCP and AES 256 CBC symmetrically encrypted messages? I also use a random salt and a transaction number.

Until now, I was thinking that successfully decrypted data would be safe. Is the case for TCP encrypted data the same? I need to have a MAC for each message and verify that between ACK's or something?

EDIT: Did some research: https://en.wikipedia.org/wiki/Authenticated_encryption

It looks like incorporating a MAC within or alongside the encrypted data is not as insecure or as complex as I was afraid.

Can both my TCP encryption and OP's file encryption problem by solved by just appending a HASH of the encrypted data to the end of the encrypted data (EtM), or appending a HASH of the plaintext data to the end of the plaintext data and then encrypting that (MtE)?

[Canada]

I think EtM is better than the alternatives. As for the rest of it, you need to explicitly describe your protocol and what security you think it guarantees. Then you should ask for review wherever you can. Same for your implementation.