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TLS 1.3 allows for the "psk_ke" and "psk_dhe_ke" key-exchange modes. Only the latter mode introduces a new ephemeral (Diffie-Hellman) key exchange, with the PSK being the only key material used in the former case. It's a compliance requirement of RFC 8446 that the server MUST NOT send a KeyShareEntry when using the "psk_ke" mode, but prior to this commit we would send a key-share based solely on whether the client sent one. This bug goes unnoticed in our internal test suite since openssl communicating with openssl can never negotiate the PSK-only key-exchange mode. However, we should still be compliant with the spec, so check whether the DHE mode was offered and don't send a key-share if it wasn't. Reviewed-by: Tomas Mraz <tomas@openssl.org> (Merged from https://github.com/openssl/openssl/pull/14749) |
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| .. | ||
| extensions_clnt.c | ||
| extensions_cust.c | ||
| extensions_srvr.c | ||
| extensions.c | ||
| README.md | ||
| statem_clnt.c | ||
| statem_dtls.c | ||
| statem_lib.c | ||
| statem_local.h | ||
| statem_srvr.c | ||
| statem.c | ||
| statem.h | ||
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 |
|_____________________________| |_______________________________|