...

                                                              |
                                                              |
                                                              V
                                                     +-----------------+
                                                     |  interim_[N-1]  |
                                                     +--------+--------+
                                                              |
     .--------------.         +------------------+            |
    |  Ratchet Tree  |        | wire_format      |            |
    |  Key Schedule  |<-------+ content          |            |
     '-------+------'         |   epoch = N-1    +------------+
             |                |   commit         |            |
             V                | signature        |            V
 +------------------------+   +------------------+   +-----------------+
 |  confirmation_key_[N]  +-->| confirmation_tag |<--+  confirmed_[N]  |
 +------------------------+   +--------+---------+   +--------+--------+
                                       |                      |
                                       |                      V
                                       |             +-----------------+
                                       +------------>|   interim_[N]   |
                                                     +--------+--------+
                                                              |
     .--------------.         +------------------+            |
    |  Ratchet Tree  |        | wire_format      |            |
    |  Key Schedule  |<-------+ content          |            |
     '-------+------'         |   epoch = N      +------------+
             |                |   commit         |            |
             V                | signature        |            V
 +------------------------+   +------------------+   +-----------------+
 | confirmation_key_[N+1] +-->| confirmation_tag |<--+ confirmed_[N+1] |
 +------------------------+   +--------+---------+   +--------+--------+
                                       |                      |
                                       |                      V
                                       |             +-----------------+
                                       +------------>|  interim_[N+1]  |
                                                     +--------+--------+
                                                              |
                                                              V

                                                             ...