openssl

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History

Matt Caswell 77815a026c Fix resumption after HRR Commit `6b1bb98fa` moved the processing of ClientHello extensions into the state machine post-processing stage. After processing s->init_num is reset to 0, so by post-processing we cannot rely on its value. Unfortunately we were using it to handle the PSK extension. This causes the handshake to fail. We were using init_num to figure out the length of ClientHello2 so we can remove it from the handshake_buffer. The handshake_buffer holds the transcript of all the messages sent so far. For PSK processing though we only want to add in a partial ClientHello2. This commit changes things so we just work out where ClientHello2 starts, working forward from the beginning of handshake_buffer. Fixes #2983 Reviewed-by: Rich Salz <rsalz@openssl.org> (Merged from https://github.com/openssl/openssl/pull/2996)		2017-03-21 10:00:44 +00:00
..
extensions_clnt.c	Fix the Padding extension	2017-03-16 15:37:41 +00:00
extensions_srvr.c	Merge early_data_info extension into early_data	2017-03-16 14:20:38 +00:00
extensions.c	Fix resumption after HRR	2017-03-21 10:00:44 +00:00
README
statem_clnt.c	Implement certificate_authorities extension	2017-03-17 18:41:56 +00:00
statem_dtls.c	Miscellaneous style tweaks based on feedback received	2017-01-30 10:18:23 +00:00
statem_lib.c	Move parsing and construction of CA names to separate functions	2017-03-17 18:41:56 +00:00
statem_locl.h	Allow signature algorithms in TLS 1.3 certificate request extensions.	2017-03-17 18:41:56 +00:00
statem_srvr.c	Support draft-19 TLS certificate request format	2017-03-17 18:41:56 +00:00
statem.c	Update end of early data processing for draft-19	2017-03-16 14:20:38 +00:00
statem.h	Update end of early data processing for draft-19	2017-03-16 14:20:38 +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 |
  |_____________________________| |_______________________________|