=pod

=head1 NAME

TLSv1_2_method, TLSv1_2_server_method, TLSv1_2_client_method,

SSL_CTX_new, 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

=head1 SYNOPSIS

 #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);

 #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

=head1 DESCRIPTION

SSL_CTX_new() creates a new B<SSL_CTX> object as framework to

establish TLS/SSL or DTLS enabled connections. An B<SSL_CTX> object is

reference counted. Creating an B<SSL_CTX> object for the first time increments

the reference count. Freeing it (using SSL_CTX_free) decrements it. When the

reference count drops to zero, any memory or resources allocated to the

B<SSL_CTX> object are freed. SSL_CTX_up_ref() increments the reference count for

an existing B<SSL_CTX> structure.

=head1 NOTES

The SSL_CTX object uses B<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.

B<method> can be of the following types:

=over 4

=item TLS_method(), TLS_server_method(), TLS_client_method()

These are the general-purpose I<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.

=item 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.

=item 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.

=item 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.

=item 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.

=item 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.

=item 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.

=item DTLSv1_2_method(), DTLSv1_2_server_method(), DTLSv1_2_client_method()

These are the version-specific methods for DTLSv1.2.

These methods are deprecated.

=item DTLSv1_method(), DTLSv1_server_method(), DTLSv1_client_method()

These are the version-specific methods for DTLSv1.

These methods are deprecated.

=back

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 I<version-flexible>

methods.

All other methods only support one specific protocol version.

Use the I<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 L<SSL_CTX_set_min_proto_version(3)>,

L<SSL_set_min_proto_version(3)>, L<SSL_CTX_set_max_proto_version(3)> and

L<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

B<SSL_OP_NO_SSLv3>, B<SSL_OP_NO_TLSv1>, B<SSL_OP_NO_TLSv1_1>,

B<SSL_OP_NO_TLSv1_3>, B<SSL_OP_NO_TLSv1_2> and B<SSL_OP_NO_TLSv1_3>

options of the

L<SSL_CTX_set_options(3)> or L<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 I<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 L<SSL_CTX_set_min_proto_version(3)> to set

the minimum protocol to at least B<TLS1_VERSION>.

=head1 RETURN VALUES

The following return values can occur:

=over 4

=item NULL

The creation of a new SSL_CTX object failed. Check the error stack to find out

the reason.

=item 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.

=back

=head1 SEE ALSO

L<SSL_CTX_set_options(3)>, L<SSL_CTX_free(3)>, L<SSL_accept(3)>,

L<SSL_CTX_set_min_proto_version(3)>, L<ssl(7)>, L<SSL_set_connect_state(3)>

=head1 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.

=head1 COPYRIGHT

Copyright 2000-2019 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the OpenSSL license (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

L<https://www.openssl.org/source/license.html>.

=cut