openssl

History

Benjamin Kaduk 7bc2bddb14 Permit the "supported_groups" extension in ServerHellos Although this is forbidden by all three(!) relevant specifications, there seem to be multiple server implementations in the wild that send it. Since we didn't check for unexpected extensions in any given message type until TLS 1.3 support was added, our previous behavior was to silently accept these extensions and pass them over to the custom extension callback (if any). In order to avoid regression of functionality, relax the check for "extension in unexpected context" for this specific case, but leave the protocol enforcment mechanism unchanged for other extensions and in other extension contexts. Leave a detailed comment to indicate what is going on. Reviewed-by: Tim Hudson <tjh@openssl.org> Reviewed-by: Matt Caswell <matt@openssl.org> (Merged from https://github.com/openssl/openssl/pull/4463)		2018-01-03 09:43:54 -06:00
..
extensions.c	Permit the "supported_groups" extension in ServerHellos	2018-01-03 09:43:54 -06:00
extensions_clnt.c	Remove spaces at end of line in ssl/statem	2017-12-17 23:04:41 +01:00
extensions_cust.c	Convert the state machine code to use SSLfatal()	2017-12-04 13:31:48 +00:00
extensions_srvr.c	Remove spaces at end of line in ssl/statem	2017-12-17 23:04:41 +01:00
README	Add a state machine README	2015-10-30 08:38:18 +00:00
statem.c	Fix the check_fatal macro	2017-12-06 14:56:28 +00:00
statem.h	Don't flush the ClientHello if we're going to send early data	2017-12-28 17:32:41 +00:00
statem_clnt.c	Don't flush the ClientHello if we're going to send early data	2017-12-28 17:32:41 +00:00
statem_dtls.c	More record layer conversions to use SSLfatal()	2017-12-08 16:42:02 +00:00
statem_lib.c	Don't flush the ClientHello if we're going to send early data	2017-12-28 17:32:41 +00:00
statem_locl.h	Don't flush the ClientHello if we're going to send early data	2017-12-28 17:32:41 +00:00
statem_srvr.c	Don't flush the ClientHello if we're going to send early data	2017-12-28 17:32:41 +00:00

README

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_locl.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 |
  |_____________________________| |_______________________________|