老范的自言自语 Walter's Solo

SFrame

January 24, 2022 by walter

There are two layers of encryptions and authentication are required:

   1.  Hop-by-hop (HBH) encryption of media, metadata, and feedback
       messages between the the endpoints and SFU

   2.  End-to-end (E2E) encryption of media between the endpoints

   While DTLS-SRTP can be used as an efficient HBH mechanism, it is
   inherently point-to-point and therefore not suitable for a SFU
   context.  In addition, given the various scenarios in which video
   calling occurs, minimizing the bandwidth overhead of end-to-end
   encryption is also an important goal

SRTP can do encryption as below

     +-------------------------------+-------------------------------+^+
     |V=2|P|X|  CC   |M|     PT      |       sequence number         | |
     +-------------------------------+-------------------------------+ |
     |                           timestamp                           | |
     +---------------------------------------------------------------+ |
     |           synchronization source (SSRC) identifier            | |
     |=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=| |
     |            contributing source (CSRC) identifiers             | |
     |                               ....                            | |
     +---------------------------------------------------------------+ |
     |                   RTP extension(s) (OPTIONAL)                 | |
   +^---------------------+------------------------------------------+ |
   | |   payload header   |                                          | |
   | +--------------------+     payload  ...                         | |
   | |                                                               | |
   +^+---------------------------------------------------------------+^+
   | :                       authentication tag                      : |
   | +---------------------------------------------------------------+ |
   |                                                                   |
   ++ Encrypted Portion                       Authenticated Portion +--+

                        Figure 1: SRTP packet format

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