Provided by: libssl-doc_3.0.5-2ubuntu1_all 
NAME
TLSv1_2_method, TLSv1_2_server_method, TLSv1_2_client_method, SSL_CTX_new, SSL_CTX_new_ex,
SSL_CTX_up_ref, SSLv3_method, SSLv3_server_method, SSLv3_client_method, TLSv1_method,
TLSv1_server_method, TLSv1_client_method, TLSv1_1_method, TLSv1_1_server_method,
TLSv1_1_client_method, TLS_method, TLS_server_method, TLS_client_method, SSLv23_method,
SSLv23_server_method, SSLv23_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 framework for TLS/SSL or DTLS enabled functions
SYNOPSIS
#include <openssl/ssl.h>
SSL_CTX *SSL_CTX_new_ex(OSSL_LIB_CTX *libctx, const char *propq,
const SSL_METHOD *method);
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);
#ifndef OPENSSL_NO_SSL3_METHOD
const SSL_METHOD *SSLv3_method(void);
const SSL_METHOD *SSLv3_server_method(void);
const SSL_METHOD *SSLv3_client_method(void);
#endif
#ifndef OPENSSL_NO_TLS1_METHOD
const SSL_METHOD *TLSv1_method(void);
const SSL_METHOD *TLSv1_server_method(void);
const SSL_METHOD *TLSv1_client_method(void);
#endif
#ifndef OPENSSL_NO_TLS1_1_METHOD
const SSL_METHOD *TLSv1_1_method(void);
const SSL_METHOD *TLSv1_1_server_method(void);
const SSL_METHOD *TLSv1_1_client_method(void);
#endif
#ifndef OPENSSL_NO_TLS1_2_METHOD
const SSL_METHOD *TLSv1_2_method(void);
const SSL_METHOD *TLSv1_2_server_method(void);
const SSL_METHOD *TLSv1_2_client_method(void);
#endif
const SSL_METHOD *DTLS_method(void);
const SSL_METHOD *DTLS_server_method(void);
const SSL_METHOD *DTLS_client_method(void);
#ifndef OPENSSL_NO_DTLS1_METHOD
const SSL_METHOD *DTLSv1_method(void);
const SSL_METHOD *DTLSv1_server_method(void);
const SSL_METHOD *DTLSv1_client_method(void);
#endif
#ifndef OPENSSL_NO_DTLS1_2_METHOD
const SSL_METHOD *DTLSv1_2_method(void);
const SSL_METHOD *DTLSv1_2_server_method(void);
const SSL_METHOD *DTLSv1_2_client_method(void);
#endif
DESCRIPTION
SSL_CTX_new_ex() creates a new SSL_CTX object, which holds various configuration and data
relevant to SSL/TLS or DTLS session establishment. These are later inherited by the SSL
object representing an active session. The method parameter specifies whether the context
will be used for the client or server side or both - for details see the "NOTES" below.
The library context libctx (see OSSL_LIB_CTX(3)) is used to provide the cryptographic
algorithms needed for the session. Any cryptographic algorithms that are used by any SSL
objects created from this SSL_CTX will be fetched from the libctx using the property query
string propq (see "ALGORITHM FETCHING" in crypto(7). Either or both the libctx or propq
parameters may be NULL.
SSL_CTX_new() does the same as SSL_CTX_new_ex() except that the default library context is
used and no property query string is specified.
An SSL_CTX object is reference counted. Creating an SSL_CTX object for the first time
increments the reference count. Freeing the SSL_CTX (using SSL_CTX_free) decrements it.
When the reference count drops to zero, any memory or resources allocated to the SSL_CTX
object are freed. SSL_CTX_up_ref() increments the reference count for an existing SSL_CTX
structure.
An SSL_CTX object should not be changed after it is used to create any SSL objects or from
multiple threads concurrently, since the implementation does not provide serialization of
access for these cases.
NOTES
On session estabilishment, by default, no peer credentials verification is done. This
must be explicitly requested, typically using SSL_CTX_set_verify(3). For verifying peer
certificates many options can be set using various functions such as
SSL_CTX_load_verify_locations(3) and SSL_CTX_set1_param(3). The
X509_VERIFY_PARAM_set_purpose(3) function can be used, also in conjunction with
SSL_CTX_get0_param(3), to set the intended purpose of the session. The default is
X509_PURPOSE_SSL_SERVER on the client side and X509_PURPOSE_SSL_CLIENT on the server side.
The SSL_CTX object uses method as the connection method. Three method variants are
available: a generic method (for either client or server use), a server-only method, and a
client-only method.
The method parameter of SSL_CTX_new_ex() and SSL_CTX_new() can be one of the following:
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 SSLv3, TLSv1, TLSv1.1, TLSv1.2 and
TLSv1.3. Applications should use these methods, and avoid the version-specific
methods described below, which are deprecated.
SSLv23_method(), SSLv23_server_method(), SSLv23_client_method()
These functions do not exist anymore, they have been renamed to TLS_method(),
TLS_server_method() and TLS_client_method() respectively. Currently, the old function
calls are renamed to the corresponding new ones by preprocessor macros, to ensure that
existing code which uses the old function names still compiles. However, using the old
function names is deprecated and new code should call the new functions instead.
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. These methods are deprecated.
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. These methods are deprecated.
TLSv1_method(), TLSv1_server_method(), TLSv1_client_method()
A TLS/SSL connection established with these methods will only understand the TLSv1
protocol. These methods are deprecated.
SSLv3_method(), SSLv3_server_method(), SSLv3_client_method()
A TLS/SSL connection established with these methods will only understand the SSLv3
protocol. The SSLv3 protocol is deprecated and should not be used.
DTLS_method(), DTLS_server_method(), DTLS_client_method()
These are the version-flexible DTLS methods. Currently supported protocols are DTLS
1.0 and DTLS 1.2.
DTLSv1_2_method(), DTLSv1_2_server_method(), DTLSv1_2_client_method()
These are the version-specific methods for DTLSv1.2. These methods are deprecated.
DTLSv1_method(), DTLSv1_server_method(), DTLSv1_client_method()
These are the version-specific methods for DTLSv1. These methods are deprecated.
SSL_CTX_new() initializes the list of ciphers, the session cache setting, the callbacks,
the keys and certificates and the options to their default values.
TLS_method(), TLS_server_method(), TLS_client_method(), DTLS_method(),
DTLS_server_method() and DTLS_client_method() are the version-flexible methods. All other
methods only support one specific protocol version. Use the version-flexible methods
instead of the version specific methods.
If you want to limit the supported protocols for the version flexible methods you can use
SSL_CTX_set_min_proto_version(3), SSL_set_min_proto_version(3),
SSL_CTX_set_max_proto_version(3) and SSL_set_max_proto_version(3) functions. Using these
functions it is possible to choose e.g. TLS_server_method() and be able to negotiate with
all possible clients, but to only allow newer protocols like TLS 1.0, TLS 1.1, TLS 1.2 or
TLS 1.3.
The list of protocols available can also be limited using the SSL_OP_NO_SSLv3,
SSL_OP_NO_TLSv1, SSL_OP_NO_TLSv1_1, SSL_OP_NO_TLSv1_3, SSL_OP_NO_TLSv1_2 and
SSL_OP_NO_TLSv1_3 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.
The SSLv3 protocol is deprecated and should generally not be used. Applications should
typically use SSL_CTX_set_min_proto_version(3) to set the minimum protocol to at least
TLS1_VERSION.
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.
SSL_CTX_up_ref() returns 1 for success and 0 for failure.
SEE ALSO
SSL_CTX_set_options(3), SSL_CTX_free(3), SSL_CTX_set_verify(3), SSL_CTX_set1_param(3),
SSL_CTX_get0_param(3), SSL_connect(3), SSL_accept(3), SSL_CTX_set_min_proto_version(3),
ssl(7), SSL_set_connect_state(3)
HISTORY
Support for SSLv2 and the corresponding SSLv2_method(), SSLv2_server_method() and
SSLv2_client_method() functions where removed in OpenSSL 1.1.0.
SSLv23_method(), SSLv23_server_method() and SSLv23_client_method() were deprecated and the
preferred TLS_method(), TLS_server_method() and TLS_client_method() functions were added
in OpenSSL 1.1.0.
All version-specific methods were deprecated in OpenSSL 1.1.0.
SSL_CTX_new_ex() was added in OpenSSL 3.0.
COPYRIGHT
Copyright 2000-2021 The OpenSSL Project Authors. All Rights Reserved.
Licensed under the Apache License 2.0 (the "License"). You may not use this file except
in compliance with the License. You can obtain a copy in the file LICENSE in the source
distribution or at <https://www.openssl.org/source/license.html>.