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.
98
99=item SSLv23_method(), SSLv23_server_method(), SSLv23_client_method()
100
101Use of these functions is deprecated. They have been replaced with the above
102TLS_method(), TLS_server_method() and TLS_client_method() respectively. New
103code should use those functions instead.
104
105=item TLSv1_2_method(), TLSv1_2_server_method(), TLSv1_2_client_method()
106
107A TLS/SSL connection established with these methods will only understand the
108TLSv1.2 protocol.
109
110=item TLSv1_1_method(), TLSv1_1_server_method(), TLSv1_1_client_method()
111
112A TLS/SSL connection established with these methods will only understand the
113TLSv1.1 protocol.
114
115=item TLSv1_method(), TLSv1_server_method(), TLSv1_client_method()
116
117A TLS/SSL connection established with these methods will only understand the
118TLSv1 protocol.
119
120=item SSLv3_method(), SSLv3_server_method(), SSLv3_client_method()
121
122A TLS/SSL connection established with these methods will only understand the
123SSLv3 protocol.
124The SSLv3 protocol is deprecated and should not be used.
125
126=item DTLS_method(), DTLS_server_method(), DTLS_client_method()
127
128These are the version-flexible DTLS methods.
129Currently supported protocols are DTLS 1.0 and DTLS 1.2.
130
131=item DTLSv1_2_method(), DTLSv1_2_server_method(), DTLSv1_2_client_method()
132
133These are the version-specific methods for DTLSv1.2.
134
135=item DTLSv1_method(), DTLSv1_server_method(), DTLSv1_client_method()
136
137These are the version-specific methods for DTLSv1.
138
139=back
140
141SSL_CTX_new() initializes the list of ciphers, the session cache setting, the
142callbacks, the keys and certificates and the options to their default values.
143
144TLS_method(), TLS_server_method(), TLS_client_method(), DTLS_method(),
145DTLS_server_method() and DTLS_client_method() are the I<version-flexible>
146methods.
147All other methods only support one specific protocol version.
148Use the I<version-flexible> methods instead of the version specific methods.
149
150If you want to limit the supported protocols for the version flexible
151methods you can use L<SSL_CTX_set_min_proto_version(3)>,
152L<SSL_set_min_proto_version(3)>, L<SSL_CTX_set_max_proto_version(3)> and
153L<SSL_set_max_proto_version(3)> functions.
154Using these functions it is possible to choose e.g. TLS_server_method()
155and be able to negotiate with all possible clients, but to only
156allow newer protocols like TLS 1.0, TLS 1.1, TLS 1.2 or TLS 1.3.
157
158The list of protocols available can also be limited using the
159B<SSL_OP_NO_SSLv3>, B<SSL_OP_NO_TLSv1>, B<SSL_OP_NO_TLSv1_1>,
160B<SSL_OP_NO_TLSv1_3>, B<SSL_OP_NO_TLSv1_2> and B<SSL_OP_NO_TLSv1_3>
161options of the
162L<SSL_CTX_set_options(3)> or L<SSL_set_options(3)> functions, but this approach
163is not recommended. Clients should avoid creating "holes" in the set of
164protocols they support. When disabling a protocol, make sure that you also
165disable either all previous or all subsequent protocol versions.
166In clients, when a protocol version is disabled without disabling I<all>
167previous protocol versions, the effect is to also disable all subsequent
168protocol versions.
169
170The SSLv3 protocol is deprecated and should generally not be used.
171Applications should typically use L<SSL_CTX_set_min_proto_version(3)> to set
172the minimum protocol to at least B<TLS1_VERSION>.
173
174=head1 RETURN VALUES
175
176The following return values can occur:
177
178=over 4
179
180=item NULL
181
182The creation of a new SSL_CTX object failed. Check the error stack to find out
183the reason.
184
185=item Pointer to an SSL_CTX object
186
187The return value points to an allocated SSL_CTX object.
188
189SSL_CTX_up_ref() returns 1 for success and 0 for failure.
190
191=back
192
193=head1 SEE ALSO
194
195L<SSL_CTX_set_options(3)>, L<SSL_CTX_free(3)>, L<SSL_accept(3)>,
196L<SSL_CTX_set_min_proto_version(3)>, L<ssl(7)>, L<SSL_set_connect_state(3)>
197
198=head1 HISTORY
199
200Support for SSLv2 and the corresponding SSLv2_method(),
201SSLv2_server_method() and SSLv2_client_method() functions where
202removed in OpenSSL 1.1.0.
203
204SSLv23_method(), SSLv23_server_method() and SSLv23_client_method()
205were deprecated and the preferred TLS_method(), TLS_server_method()
206and TLS_client_method() functions were added in OpenSSL 1.1.0.
207
208All version-specific methods were deprecated in OpenSSL 1.1.0.
209
210=head1 COPYRIGHT
211
212Copyright 2000-2019 The OpenSSL Project Authors. All Rights Reserved.
213
214Licensed under the OpenSSL license (the "License").  You may not use
215this file except in compliance with the License.  You can obtain a copy
216in the file LICENSE in the source distribution or at
217L<https://www.openssl.org/source/license.html>.
218
219=cut
220