SSL_CTX_new() creates a new SSL_CTX object as framework to establish
TLS/SSL enabled connections.
NOTES
The SSL_CTX object uses method as connection method. The methods exist
in a generic type (for client and server use), a server only type, and a
client only type. method can be of the following types:
A TLS/SSL connection established with these methods will only understand
the SSLv2 protocol. A client will send out SSLv2 client hello messages
and will also indicate that it only understand SSLv2. A server will only
understand SSLv2 client hello messages.
A TLS/SSL connection established with these methods will only understand the
SSLv3 protocol. A client will send out SSLv3 client hello messages
and will indicate that it only understands SSLv3. A server will only understand
SSLv3 client hello messages. This especially means, that it will
not understand SSLv2 client hello messages which are widely used for
compatibility reasons, see SSLv23_*_method().
A TLS/SSL connection established with these methods will only understand the
TLSv1 protocol. A client will send out TLSv1 client hello messages
and will indicate that it only understands TLSv1. A server will only understand
TLSv1 client hello messages. This especially means, that it will
not understand SSLv2 client hello messages which are widely used for
compatibility reasons, see SSLv23_*_method(). It will also not understand
SSLv3 client hello messages.
A TLS/SSL connection established with these methods will understand the SSLv2,
SSLv3, and TLSv1 protocol. A client will send out SSLv2 client hello messages
and will indicate that it also understands SSLv3 and TLSv1. A server will
understand SSLv2, SSLv3, and TLSv1 client hello messages. This is the best
choice when compatibility is a concern.
The list of protocols available can later be limited using the SSL_OP_NO_SSLv2,
SSL_OP_NO_SSLv3, SSL_OP_NO_TLSv1 options of the SSL_CTX_set_options() or
SSL_set_options() functions. Using these options it is possible to choose
e.g. SSLv23_server_method() and be able to negotiate with all possible
clients, but to only allow newer protocols like SSLv3 or TLSv1.
SSL_CTX_new() initializes the list of ciphers, the session cache setting,
the callbacks, the keys and certificates, and the options to its default
values.
RETURN VALUES
The following return values can occur:
NULL
The creation of a new SSL_CTX object failed. Check the error stack to
find out the reason.
Pointer to an SSL_CTX object
The return value points to an allocated SSL_CTX object.
