SSL_CTX_new

 #include <openssl/ssl.h>
 SSL_CTX *SSL_CTX_new(const SSL_METHOD *method);

SSL_CTX_new() creates a new SSL_CTX object as framework to establish TLS/SSL enabled connections.

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:

SSLv2_method(void), SSLv2_server_method(void), SSLv2_client_method(void)

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.

SSLv3_method(void), SSLv3_server_method(void), SSLv3_client_method(void)

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().

TLSv1_method(void), TLSv1_server_method(void), TLSv1_client_method(void)

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.

SSLv23_method(void), SSLv23_server_method(void), SSLv23_client_method(void)

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.

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.

SSL_CTX_free(3), SSL_accept(3), ssl(3), SSL_set_connect_state(3)