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Diffstat (limited to 'openssl-1.1.0h/ssl/statem/README')
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diff --git a/openssl-1.1.0h/ssl/statem/README b/openssl-1.1.0h/ssl/statem/README new file mode 100644 index 0000000..145c69d --- /dev/null +++ b/openssl-1.1.0h/ssl/statem/README @@ -0,0 +1,63 @@ +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 | + |_____________________________| |_______________________________| + |