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openssl/ssl/statem
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Tomas Mraz f378755d62 statem_lib.c: Remove TODOs that are unnecessary 
If the EVP_MD_CTX_ctrl is deprecated the code will
generate deprecation warnings. So there is no point in marking
all EVP_MD_CTX_ctrl() calls with TODOs.

Reviewed-by: Paul Dale <pauli@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/14367)
2021-03-03 10:00:21 +10:00
..
extensions_clnt.c Update copyright year 2021-02-18 15:05:17 +00:00
extensions_cust.c Update copyright year 2021-02-18 15:05:17 +00:00
extensions_srvr.c Update copyright year 2021-02-18 15:05:17 +00:00
extensions.c Remove OPENSSL_NO_EC guards from libssl 2021-02-05 15:22:43 +00:00
README.md Fix many MarkDown issues in {NOTES*,README*,HACKING,LICENSE}.md files 2020-07-05 11:29:43 +02:00
statem_clnt.c Implement EVP_PKEY_param_check_quick() and use it in libssl 2021-02-15 14:17:36 +10:00
statem_dtls.c SSL: refactor all SSLfatal() calls 2020-11-11 12:12:23 +01:00
statem_lib.c statem_lib.c: Remove TODOs that are unnecessary 2021-03-03 10:00:21 +10:00
statem_local.h Remove OPENSSL_NO_EC guards from libssl 2021-02-05 15:22:43 +00:00
statem_srvr.c Deprecate the libssl level SRP APIs 2021-02-12 08:47:32 +00:00
statem.c Update copyright year 2021-01-28 13:54:57 +01:00
statem.h Update copyright year 2021-01-28 13:54:57 +01:00

README.md

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_both.c               | | statem_dtls.c                 |
|                             | |                               |
| Non core functions common   | | Non core functions common to  |
| to both servers and clients | | both DTLS servers and clients |
|_____________________________| |_______________________________|