An encryption algorithm and a key will be negotiated during the key exchange. When encryption is in effect, the packet length, padding length, payload, and padding fields of each packet MUST be encrypted with the given algorithm.
I have a serious question now that you mentioned crypto. There's a CTF challenge asking me to provide a file and HMAC, and says the HMAC should be 16-byte (32 hex characters). I tried MD4 and MD5 HMAC, but it says "HMAC mismatch".