Matt Caswell 91c7ab27ce Set the server sig algs before calling the session_secret_cb		5 달 전
..
README.md	8b6a7da304 ssl: Correct filename in README	3 년 전
extensions.c	f290663148 Fix implementation of `PreferNoDHEKEX` option.	10 달 전
extensions_clnt.c	48e3cf25a8 ssl/statem: Replace size_t with int and add the checks	5 달 전
extensions_cust.c	bc0773bbbd Fix a possible use-after-free in custom_exts_free	10 달 전
extensions_srvr.c	48e3cf25a8 ssl/statem: Replace size_t with int and add the checks	5 달 전
statem.c	e158ada6a7 Remove the old buffer management code	1 년 전
statem_clnt.c	972ee925b1 Use empty renegotiate extension instead of SCSV for TLS > 1.0	5 달 전
statem_dtls.c	b646179229 Copyright year updates	5 달 전
statem_lib.c	b646179229 Copyright year updates	5 달 전
statem_local.h	3c95ef22df RFC7250 (RPK) support	1 년 전
statem_srvr.c	91c7ab27ce Set the server sig algs before calling the session_secret_cb	4 달 전

State Machine Design

This file provides some guidance on the thinking behind the design of the state machine code to aid future maintenance.

The state machine code replaces an older state machine present in OpenSSL versions 1.0.2 and below. The new state machine has the following objectives:

Remove duplication of state code between client and server
Remove duplication of state code between TLS and DTLS
Simplify transitions and bring the logic together in a single location so that it is easier to validate
Remove duplication of code between each of the message handling functions
Receive a message first and then work out whether that is a valid transition - not the other way around (the other way causes lots of issues where we are expecting one type of message next but actually get something else)
Separate message flow state from handshake state (in order to better understand each)
- message flow state = when to flush buffers; handling restarts in the event of NBIO events; handling the common flow of steps for reading a message and the common flow of steps for writing a message etc
- handshake state = what handshake message are we working on now
Control complexity: only the state machine can change state: keep all the state changes local to the state machine component

The message flow state machine is divided into a reading sub-state machine and a writing sub-state machine. See the source comments in statem.c for a more detailed description of the various states and transitions possible.

Conceptually the state machine component is designed as follows:

                      libssl
                         |
-------------------------|-----statem.h------------------------------------
                         |
                  _______V____________________
                 |                            |
                 |    statem.c                |
                 |                            |
                 |    Core state machine code |
                 |____________________________|
      statem_local.h     ^          ^
               _________|          |_______
              |                            |
 _____________|____________   _____________|____________
|                          | |                          |
| statem_clnt.c            | | statem_srvr.c            |
|                          | |                          |
| TLS/DTLS client specific | | TLS/DTLS server specific |
| state machine code       | | state machine code       |
|__________________________| |__________________________|
             |        |_______________|__       |
             |        ________________|  |      |
             |       |                   |      |
 ____________V_______V________   ________V______V_______________
|                             | |                               |
| statem_lib.c                | | statem_dtls.c                 |
|                             | |                               |
| Non core functions common   | | Non core functions common to  |
| to both servers and clients | | both DTLS servers and clients |
|_____________________________| |_______________________________|

README.md

State Machine Design