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SSL_CTX_NEW(3) Library Functions Manual SSL_CTX_NEW(3)

SSL_CTX_new, SSL_CTX_up_ref, TLS_method, TLS_server_method, TLS_client_method, SSLv23_method, SSLv23_server_method, SSLv23_client_method, TLSv1_method, TLSv1_server_method, TLSv1_client_method, TLSv1_1_method, TLSv1_1_server_method, TLSv1_1_client_method, TLSv1_2_method, TLSv1_2_server_method, TLSv1_2_client_method, DTLSv1_method, DTLSv1_server_method, DTLSv1_client_method
create a new SSL_CTX object as framework for TLS/SSL enabled functions

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

SSL_CTX_new() creates a new SSL_CTX object as framework to establish TLS/SSL or DTLS enabled connections. It initializes the list of ciphers, the session cache setting, the callbacks, the keys and certificates, and the options to its default values.
An SSL_CTX object is reference counted. Creating a new SSL_CTX object sets its reference count to 1. Calling SSL_CTX_up_ref() on it increments the reference count by 1. Calling SSL_CTX_free(3) on it decrements the reference count by 1. When the reference count drops to zero, any memory or resources allocated to the SSL_CTX object are freed.
The SSL_CTX object uses method as its 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:
TLS_method(), TLS_server_method(), TLS_client_method()
These are the general-purpose version-flexible SSL/TLS methods. The actual protocol version used will be negotiated to the highest version mutually supported by the client and the server. The supported protocols are TLSv1, TLSv1.1 and TLSv1.2. Applications should use these methods and avoid the version-specific methods described below.
SSLv23_method(), SSLv23_server_method(), SSLv23_client_method()
Use of these functions is deprecated. They have been replaced with the above TLS_method(), TLS_server_method(), and TLS_client_method(), respectively. New code should use those functions instead.
TLSv1_method(), TLSv1_server_method(), TLSv1_client_method()
A TLS/SSL connection established with these methods will only understand the TLSv1 protocol.
TLSv1_1_method(), TLSv1_1_server_method(), TLSv1_1_client_method()
A TLS/SSL connection established with these methods will only understand the TLSv1.1 protocol.
TLSv1_2_method(), TLSv1_2_server_method(), TLSv1_2_client_method()
A TLS/SSL connection established with these methods will only understand the TLSv1.2 protocol.
DTLSv1_method(), DTLSv1_server_method(), DTLSv1_client_method()
These are the version-specific methods for DTLSv1.
The list of protocols available can also be limited using the SSL_OP_NO_TLSv1, SSL_OP_NO_TLSv1_1, and SSL_OP_NO_TLSv1_2 options of the SSL_CTX_set_options(3) or SSL_set_options(3) functions, but this approach is not recommended. Clients should avoid creating "holes" in the set of protocols they support. When disabling a protocol, make sure that you also disable either all previous or all subsequent protocol versions. In clients, when a protocol version is disabled without disabling all previous protocol versions, the effect is to also disable all subsequent protocol versions.

SSL_CTX_new() returns a pointer to the newly allocated object or NULL on failure. Check the error stack to find out the reason for failure.
SSL_CTX_up_ref() returns 1 for success or 0 for failure.

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

SSL_CTX_new() first appeared in SSLeay 0.5.1. SSLv23_method(), SSLv23_server_method(), and SSLv23_client_method() first appeared in SSLeay 0.8.0. TLSv1_method(), TLSv1_server_method(), and TLSv1_client_method() first appeared in SSLeay 0.9.0. All these functions have been available since OpenBSD 2.4.
DTLSv1_method(), DTLSv1_server_method(), and DTLSv1_client_method() first appeared in OpenSSL 0.9.8 and have been available since OpenBSD 4.5.
TLSv1_1_method(), TLSv1_1_server_method(), TLSv1_1_client_method(), TLSv1_2_method(), TLSv1_2_server_method(), and TLSv1_2_client_method() first appeared in OpenSSL 1.0.1 and have been available since OpenBSD 5.3.
TLS_method(), TLS_server_method(), and TLS_client_method() first appeared in OpenSSL 1.1.0 and have been available since OpenBSD 5.8.
SSL_CTX_up_ref() first appeared in OpenSSL 1.1.0 and has been available since OpenBSD 6.3.
March 27, 2018 OpenBSD-current