ssl - OpenSSL let the server and client negotiate the method -

following outdated tutorial managed create https server using openssl tls1.2, , i'm proud of ;)

however tls 1.2 supported in latest browsers , have kind of negotiation of protocol between client , server, i'm sure can done, i'm not able find how! if client supports tls1.0, use that. , if supports sslv3, use that. not sure sslv2, maybe better leave that...

the code use right is:

ssl_library_init(); openssl_add_all_algorithms(); ssl_load_error_strings(); ssl_method = tlsv1_2_server_method(); ssl_ctx = ssl_ctx_new(ssl_method); 

then server certificates loaded , ssl_ctx shared among connections. when client accepted server socket encapsulated in ssl object (whatever represents):

ssl = ssl_new(ssl_ctx); ssl_set_fd(ssl, client_socket); ssl_accept(ssl); 

so guess has changed in ssl_ctx creation allow more methods... idea?

<rant> no decent, extensive documentation can found openssl, best available 10 years old tutorial! </rant>

thanks in advance.

you using sslv23_method() (and friends) instead of specific method (e.g. tlsv1_2_server_method() in example). sends sslv2 clienthello specifies highest protocol supported. outdated man page says:

sslv23_method(void), sslv23_server_method(void), sslv23_client_method(void)

a tls/ssl connection established these methods understand sslv2, sslv3, , tlsv1 protocol. client send out sslv2 client hello messages , indicate understands sslv3 , tlsv1. server understand sslv2, sslv3, , tlsv1 client hello messages. best choice when compatibility concern.

this online man page doesn't discuss newer tlsv1_1 , tlsv1_2 protocols, verified in 1.0.1g source of s23_clnt.c sslv23_method() includes them.

you limit protocols accept ssl_ctx_set_options():

the list of protocols available can later limited using ssl_op_no_sslv2, ssl_op_no_sslv3, ssl_op_no_tlsv1 options of ssl_ctx_set_options() or ssl_set_options() functions. using these options possible choose e.g. sslv23_server_method() , able negotiate possible clients, allow newer protocols sslv3 or tlsv1.

note, however, can't enable arbitrary sets of protocols, contiguous protocols in sslv2, sslv3, tlsv1, tlsv1_1, tlsv1_2. example, can't choose sslv3 , tlsv1_1, omitting tlsv1. comment in source explains why:

ssl_op_no_x disables protocols above x if there protocols below x enabled. required in order maintain "version capability" vector contiguous. if application wants disable tls1.0 in favour of tls1>=1, insufficient pass ssl_no_tlsv1, answer ssl_op_no_tlsv1|ssl_op_no_sslv3|ssl_op_no_sslv2.