3.1.5.2 Post-Authentication Messages
If a graph security provider is configured on the local node, every message that is received on a connection in state IN_CON_AUTHENTICATED or OUT_CON_AUTHENTICATED MUST be forwarded to the graph security provider to be decrypted before it can be processed by the node as a received Message. If the graph security provider returns an error, the message MUST be discarded.
Each decrypted message (or unencrypted received message, if no graph security provider is Configured) MUST begin with the same message header (see PEER_MESSAGE (section 2.2.1.2)), which contains the type of the message. If an unknown message type (outside the range 0x00 through 0x0E) is received, or if a known message is received, but cannot be parsed properly (with a Message Size less than 0x00000008, or a version field value other than 0x10, or any other field invalid), the connection MUST be terminated, and the invalid message otherwise ignored.