digraph {

        /* could shave a RTT by committing to the nameplate early, before
        finishing the rest of the code input. While the user is still
        typing/completing the code, we claim the nameplate, open the mailbox,
        and retrieve the peer's PAKE message. Then as soon as the user
        finishes entering the code, we build our own PAKE message, send PAKE,
        compute the key, send VERSION. Starting from the Return, this saves
        two round trips. OTOH it adds consequences to hitting Tab. */

        start [label="Receive\nMachine" style="dotted"]

        S0 [label="S0:\nunknown key" color="orange"]
        S0 -> P0_got_key [label="got_key" color="orange"]

        P0_got_key [shape="box" label="record key" color="orange"]
        P0_got_key -> S1 [color="orange"]

        S1 [label="S1:\nunverified key" color="orange"]
        S1 -> P_mood_scary [label="got_message\n(bad)"]
        S1 -> P1_accept_msg [label="got_message\n(good)" color="orange"]
        P1_accept_msg [shape="box" label="S.got_verified_key\nB.happy\nB.got_verifier\nB.got_message"
                       color="orange"]
        P1_accept_msg -> S2 [color="orange"]

        S2 [label="S2:\nverified key" color="green"]

        S2 -> P2_accept_msg [label="got_message\n(good)" color="orange"]
        S2 -> P_mood_scary [label="got_message(bad)"]

        P2_accept_msg [label="B.got_message" shape="box" color="orange"]
        P2_accept_msg -> S2 [color="orange"]

        P_mood_scary [shape="box" label="B.scared" color="red"]
        P_mood_scary -> S3 [color="red"]

        S3 [label="S3:\nscared" color="red"]
        S3 -> S3 [label="got_message"]
}