1=pod
2
3=head1 NAME
4
5TLSv1_2_method, TLSv1_2_server_method, TLSv1_2_client_method,
6SSL_CTX_new, SSL_CTX_up_ref, SSLv3_method, SSLv3_server_method,
7SSLv3_client_method, TLSv1_method, TLSv1_server_method, TLSv1_client_method,
8TLSv1_1_method, TLSv1_1_server_method, TLSv1_1_client_method, TLS_method,
9TLS_server_method, TLS_client_method, SSLv23_method, SSLv23_server_method,
10SSLv23_client_method, DTLS_method, DTLS_server_method, DTLS_client_method,
11DTLSv1_method, DTLSv1_server_method, DTLSv1_client_method,
12DTLSv1_2_method, DTLSv1_2_server_method, DTLSv1_2_client_method
13- create a new SSL_CTX object as framework for TLS/SSL or DTLS enabled
14functions
15
16=head1 SYNOPSIS
17
18 #include <openssl/ssl.h>
19
20 SSL_CTX *SSL_CTX_new(const SSL_METHOD *method);
21 int SSL_CTX_up_ref(SSL_CTX *ctx);
22
23 const SSL_METHOD *TLS_method(void);
24 const SSL_METHOD *TLS_server_method(void);
25 const SSL_METHOD *TLS_client_method(void);
26
27 const SSL_METHOD *SSLv23_method(void);
28 const SSL_METHOD *SSLv23_server_method(void);
29 const SSL_METHOD *SSLv23_client_method(void);
30
31 #ifndef OPENSSL_NO_SSL3_METHOD
32 const SSL_METHOD *SSLv3_method(void);
33 const SSL_METHOD *SSLv3_server_method(void);
34 const SSL_METHOD *SSLv3_client_method(void);
35 #endif
36
37 #ifndef OPENSSL_NO_TLS1_METHOD
38 const SSL_METHOD *TLSv1_method(void);
39 const SSL_METHOD *TLSv1_server_method(void);
40 const SSL_METHOD *TLSv1_client_method(void);
41 #endif
42
43 #ifndef OPENSSL_NO_TLS1_1_METHOD
44 const SSL_METHOD *TLSv1_1_method(void);
45 const SSL_METHOD *TLSv1_1_server_method(void);
46 const SSL_METHOD *TLSv1_1_client_method(void);
47 #endif
48
49 #ifndef OPENSSL_NO_TLS1_2_METHOD
50 const SSL_METHOD *TLSv1_2_method(void);
51 const SSL_METHOD *TLSv1_2_server_method(void);
52 const SSL_METHOD *TLSv1_2_client_method(void);
53 #endif
54
55 const SSL_METHOD *DTLS_method(void);
56 const SSL_METHOD *DTLS_server_method(void);
57 const SSL_METHOD *DTLS_client_method(void);
58
59 #ifndef OPENSSL_NO_DTLS1_METHOD
60 const SSL_METHOD *DTLSv1_method(void);
61 const SSL_METHOD *DTLSv1_server_method(void);
62 const SSL_METHOD *DTLSv1_client_method(void);
63 #endif
64
65 #ifndef OPENSSL_NO_DTLS1_2_METHOD
66 const SSL_METHOD *DTLSv1_2_method(void);
67 const SSL_METHOD *DTLSv1_2_server_method(void);
68 const SSL_METHOD *DTLSv1_2_client_method(void);
69 #endif
70
71=head1 DESCRIPTION
72
73SSL_CTX_new() creates a new B<SSL_CTX> object as framework to
74establish TLS/SSL or DTLS enabled connections. An B<SSL_CTX> object is
75reference counted. Creating an B<SSL_CTX> object for the first time increments
76the reference count. Freeing it (using SSL_CTX_free) decrements it. When the
77reference count drops to zero, any memory or resources allocated to the
78B<SSL_CTX> object are freed. SSL_CTX_up_ref() increments the reference count for
79an existing B<SSL_CTX> structure.
80
81=head1 NOTES
82
83The SSL_CTX object uses B<method> as connection method.
84The methods exist in a generic type (for client and server use), a server only
85type, and a client only type.
86B<method> can be of the following types:
87
88=over 4
89
90=item TLS_method(), TLS_server_method(), TLS_client_method()
91
92These are the general-purpose I<version-flexible> SSL/TLS methods.
93The actual protocol version used will be negotiated to the highest version
94mutually supported by the client and the server.
95The supported protocols are SSLv3, TLSv1, TLSv1.1, TLSv1.2 and TLSv1.3.
96Applications should use these methods, and avoid the version-specific
97methods described below, which are deprecated.
98
99=item SSLv23_method(), SSLv23_server_method(), SSLv23_client_method()
100
101These functions do not exist anymore, they have been renamed to
102TLS_method(), TLS_server_method() and TLS_client_method() respectively.
103Currently, the old function calls are renamed to the corresponding new
104ones by preprocessor macros, to ensure that existing code which uses the
105old function names still compiles. However, using the old function names
106is deprecated and new code should call the new functions instead.
107
108=item TLSv1_2_method(), TLSv1_2_server_method(), TLSv1_2_client_method()
109
110A TLS/SSL connection established with these methods will only understand the
111TLSv1.2 protocol. These methods are deprecated.
112
113=item TLSv1_1_method(), TLSv1_1_server_method(), TLSv1_1_client_method()
114
115A TLS/SSL connection established with these methods will only understand the
116TLSv1.1 protocol.  These methods are deprecated.
117
118=item TLSv1_method(), TLSv1_server_method(), TLSv1_client_method()
119
120A TLS/SSL connection established with these methods will only understand the
121TLSv1 protocol. These methods are deprecated.
122
123=item SSLv3_method(), SSLv3_server_method(), SSLv3_client_method()
124
125A TLS/SSL connection established with these methods will only understand the
126SSLv3 protocol.
127The SSLv3 protocol is deprecated and should not be used.
128
129=item DTLS_method(), DTLS_server_method(), DTLS_client_method()
130
131These are the version-flexible DTLS methods.
132Currently supported protocols are DTLS 1.0 and DTLS 1.2.
133
134=item DTLSv1_2_method(), DTLSv1_2_server_method(), DTLSv1_2_client_method()
135
136These are the version-specific methods for DTLSv1.2.
137These methods are deprecated.
138
139=item DTLSv1_method(), DTLSv1_server_method(), DTLSv1_client_method()
140
141These are the version-specific methods for DTLSv1.
142These methods are deprecated.
143
144=back
145
146SSL_CTX_new() initializes the list of ciphers, the session cache setting, the
147callbacks, the keys and certificates and the options to their default values.
148
149TLS_method(), TLS_server_method(), TLS_client_method(), DTLS_method(),
150DTLS_server_method() and DTLS_client_method() are the I<version-flexible>
151methods.
152All other methods only support one specific protocol version.
153Use the I<version-flexible> methods instead of the version specific methods.
154
155If you want to limit the supported protocols for the version flexible
156methods you can use L<SSL_CTX_set_min_proto_version(3)>,
157L<SSL_set_min_proto_version(3)>, L<SSL_CTX_set_max_proto_version(3)> and
158L<SSL_set_max_proto_version(3)> functions.
159Using these functions it is possible to choose e.g. TLS_server_method()
160and be able to negotiate with all possible clients, but to only
161allow newer protocols like TLS 1.0, TLS 1.1, TLS 1.2 or TLS 1.3.
162
163The list of protocols available can also be limited using the
164B<SSL_OP_NO_SSLv3>, B<SSL_OP_NO_TLSv1>, B<SSL_OP_NO_TLSv1_1>,
165B<SSL_OP_NO_TLSv1_3>, B<SSL_OP_NO_TLSv1_2> and B<SSL_OP_NO_TLSv1_3>
166options of the
167L<SSL_CTX_set_options(3)> or L<SSL_set_options(3)> functions, but this approach
168is not recommended. Clients should avoid creating "holes" in the set of
169protocols they support. When disabling a protocol, make sure that you also
170disable either all previous or all subsequent protocol versions.
171In clients, when a protocol version is disabled without disabling I<all>
172previous protocol versions, the effect is to also disable all subsequent
173protocol versions.
174
175The SSLv3 protocol is deprecated and should generally not be used.
176Applications should typically use L<SSL_CTX_set_min_proto_version(3)> to set
177the minimum protocol to at least B<TLS1_VERSION>.
178
179=head1 RETURN VALUES
180
181The following return values can occur:
182
183=over 4
184
185=item NULL
186
187The creation of a new SSL_CTX object failed. Check the error stack to find out
188the reason.
189
190=item Pointer to an SSL_CTX object
191
192The return value points to an allocated SSL_CTX object.
193
194SSL_CTX_up_ref() returns 1 for success and 0 for failure.
195
196=back
197
198=head1 SEE ALSO
199
200L<SSL_CTX_set_options(3)>, L<SSL_CTX_free(3)>, L<SSL_accept(3)>,
201L<SSL_CTX_set_min_proto_version(3)>, L<ssl(7)>, L<SSL_set_connect_state(3)>
202
203=head1 HISTORY
204
205Support for SSLv2 and the corresponding SSLv2_method(),
206SSLv2_server_method() and SSLv2_client_method() functions where
207removed in OpenSSL 1.1.0.
208
209SSLv23_method(), SSLv23_server_method() and SSLv23_client_method()
210were deprecated and the preferred TLS_method(), TLS_server_method()
211and TLS_client_method() functions were added in OpenSSL 1.1.0.
212
213All version-specific methods were deprecated in OpenSSL 1.1.0.
214
215=head1 COPYRIGHT
216
217Copyright 2000-2019 The OpenSSL Project Authors. All Rights Reserved.
218
219Licensed under the OpenSSL license (the "License").  You may not use
220this file except in compliance with the License.  You can obtain a copy
221in the file LICENSE in the source distribution or at
222L<https://www.openssl.org/source/license.html>.
223
224=cut
225