SSL_CTX_NEW(3) | Library Functions Manual | SSL_CTX_NEW(3)

# NAME

`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`, `DTLS_method`, `DTLS_server_method`, `DTLS_client_method`, `DTLSv1_method`, `DTLSv1_server_method`, `DTLSv1_client_method`, `DTLSv1_2_method`, `DTLSv1_2_server_method`, `DTLSv1_2_client_method` — create a new SSL_CTX object as a framework for TLS enabled functions

# SYNOPSIS

library “libssl” libcrypto
`#include <openssl/ssl.h>`

SSL_CTX *
`SSL_CTX_new`(const SSL_METHOD *method);

int
`SSL_CTX_up_ref`(SSL_CTX *ctx);

const SSL_METHOD *
`TLS_method`(void);

const SSL_METHOD *
`TLS_server_method`(void);

const SSL_METHOD *
`TLS_client_method`(void);

const SSL_METHOD *
`SSLv23_method`(void);

const SSL_METHOD *
`SSLv23_server_method`(void);

const SSL_METHOD *
`SSLv23_client_method`(void);

const SSL_METHOD *
`TLSv1_method`(void);

const SSL_METHOD *
`TLSv1_server_method`(void);

const SSL_METHOD *
`TLSv1_client_method`(void);

const SSL_METHOD *
`TLSv1_1_method`(void);

const SSL_METHOD *
`TLSv1_1_server_method`(void);

const SSL_METHOD *
`TLSv1_1_client_method`(void);

const SSL_METHOD *
`TLSv1_2_method`(void);

const SSL_METHOD *
`TLSv1_2_server_method`(void);

const SSL_METHOD *
`TLSv1_2_client_method`(void);

const SSL_METHOD *
`DTLS_method`(void);

const SSL_METHOD *
`DTLS_server_method`(void);

const SSL_METHOD *
`DTLS_client_method`(void);

const SSL_METHOD *
`DTLSv1_method`(void);

const SSL_METHOD *
`DTLSv1_server_method`(void);

const SSL_METHOD *
`DTLSv1_client_method`(void);

const SSL_METHOD *
`DTLSv1_2_method`(void);

const SSL_METHOD *
`DTLSv1_2_server_method`(void);

const SSL_METHOD *
`DTLSv1_2_client_method`(void);

# DESCRIPTION

`SSL_CTX_new`() creates a new SSL_CTX object as a framework to establish TLS or DTLS enabled connections. It initializes the list of ciphers, the session cache setting, the callbacks, the keys and certificates, the options, and the security level 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, which can be:

`TLS_method`()
  The general-purpose version-flexible TLS method. The 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, TLSv1.2, and TLSv1.3.
`DTLS_method`()
  The version-flexible DTLS method. The currently supported protocols are DTLSv1 and DTLSv1.2.

The following method arguments are deprecated:

`TLS_server_method`(), `TLS_client_method`(), `SSLv23_method`(), `SSLv23_server_method`(), `SSLv23_client_method`()
  Deprecated aliases for `TLS_method`().
`DTLS_server_method`(), `DTLS_client_method`()
  Deprecated aliases for `DTLS_method`().
`TLSv1_method`(), `TLSv1_server_method`(), `TLSv1_client_method`()
  A connection established with these methods will only understand the TLSv1 protocol.
`TLSv1_1_method`(), `TLSv1_1_server_method`(), `TLSv1_1_client_method`()
  A connection established with these methods will only understand the TLSv1.1 protocol.
`TLSv1_2_method`(), `TLSv1_2_server_method`(), `TLSv1_2_client_method`()
  A 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.
`DTLSv1_2_method`(), `DTLSv1_2_server_method`(), `DTLSv1_2_client_method`() These are the version-specific methods for DTLSv1.2.

In LibreSSL, the methods containing the substrings “_server” or “_client” in their names return the same objects as the methods without these substrings.

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.

DTLSv1 and DTLSv1.2 can be disabled with SSL_CTX_set_options(3) or SSL_set_options(3) using the `SSL_OP_NO_DTLSv1` and `SSL_OP_NO_DTLSv1_2` options, respectively.

# RETURN VALUES

`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.

`TLS_method`() and the other `*_method`() functions return pointers to constant static objects.

# SEE ALSO

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

# HISTORY

`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.

`DTLS_method`(), `DTLS_server_method`(), and `DTLS_client_method`() first appeared in OpenSSL 1.0.2 and have been available since OpenBSD 6.5.

`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.

`DTLSv1_2_method`(), `DTLSv1_2_server_method`(), and `DTLSv1_2_client_method`() first appeared in OpenSSL 1.1.0 and have been available since OpenBSD 6.9.

June 8, 2025 | Debian