This document describes an extension to the TCP Authentication Option (TCP-AO) to encrypt the TCP segment payload in addition to providing TCP-AO's authentication of the payload, TCP header, and IP pseudoheader. This extension augments how the packet contents and headers are processed and which keys are derived, and adds a capability for in-band coordination of unauthenticated Diffie- Hellman key exchange at connection establishment. The extension preserves key rollover coordination and protection of long-lived connections.