Host A                                  Host B
       ------------------------                       ----------
       Address A1    Address A2                       Address B1
       ----------    ----------                       ----------
           |             |                                |
           |             |  SYN + MP_CAPABLE              |
           |--------------------------------------------->|
           |<---------------------------------------------|
           |          SYN/ACK + MP_CAPABLE(Key-B)         |
           |             |                                |
           |        ACK + MP_CAPABLE(Key-A, Key-B)        |
           |--------------------------------------------->|
           |             |                                |
           |             |   SYN + MP_JOIN(Token-B, R-A)  |
           |             |------------------------------->|
           |             |<-------------------------------|
           |             | SYN/ACK + MP_JOIN(HMAC-B, R-B) |
           |             |                                |
           |             |     ACK + MP_JOIN(HMAC-A)      |
           |             |------------------------------->|
           |             |<-------------------------------|
           |             |             ACK                |

       HMAC-A = HMAC(Key=(Key-A + Key-B), Msg=(R-A + R-B))
       HMAC-B = HMAC(Key=(Key-B + Key-A), Msg=(R-B + R-A))