Outer Header                           
  +-+-+---+--------+---------------+          
  |v|t|TKL|new code| Message ID    |          
  +-+-+---+--------+---------------+....+     
  | Token                               |     
  +--------------------------------.....+     
  | Options (IU)             |               
  .                          .               
  . OSCORE Option            .               
  +------+-------------------+               
  | 0xFF |                                  
  +------+---------------------------+
  |                                  |
  | Ciphertext: Encrypted Inner      |
  |             Header and Payload   |
  |             + Authentication Tag |
  |                                  |
  +----------------------------------+