SSL_CTX_new.pod revision 279264 
1=pod
2
3=head1 NAME
4
5SSL_CTX_new - create a new SSL_CTX object as framework for TLS/SSL enabled functions
6
7=head1 SYNOPSIS
8
9 #include <openssl/ssl.h>
10
11 SSL_CTX *SSL_CTX_new(const SSL_METHOD *method);
12
13=head1 DESCRIPTION
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15SSL_CTX_new() creates a new B<SSL_CTX> object as framework to establish
16TLS/SSL enabled connections.
17
18=head1 NOTES
19
20The SSL_CTX object uses B<method> as connection method. The methods exist
21in a generic type (for client and server use), a server only type, and a
22client only type. B<method> can be of the following types:
23
24=over 4
25
26=item SSLv2_method(void), SSLv2_server_method(void), SSLv2_client_method(void)
27
28A TLS/SSL connection established with these methods will only understand
29the SSLv2 protocol. A client will send out SSLv2 client hello messages
30and will also indicate that it only understand SSLv2. A server will only
31understand SSLv2 client hello messages.
32
33=item SSLv3_method(void), SSLv3_server_method(void), SSLv3_client_method(void)
34
35A TLS/SSL connection established with these methods will only understand the
36SSLv3 protocol. A client will send out SSLv3 client hello messages
37and will indicate that it only understands SSLv3. A server will only understand
38SSLv3 client hello messages. This especially means, that it will
39not understand SSLv2 client hello messages which are widely used for
40compatibility reasons, see SSLv23_*_method().
41
42=item TLSv1_method(void), TLSv1_server_method(void), TLSv1_client_method(void)
43
44A TLS/SSL connection established with these methods will only understand the
45TLSv1 protocol. A client will send out TLSv1 client hello messages
46and will indicate that it only understands TLSv1. A server will only understand
47TLSv1 client hello messages. This especially means, that it will
48not understand SSLv2 client hello messages which are widely used for
49compatibility reasons, see SSLv23_*_method(). It will also not understand
50SSLv3 client hello messages.
51
52=item SSLv23_method(void), SSLv23_server_method(void), SSLv23_client_method(void)
53
54A TLS/SSL connection established with these methods may understand the SSLv2,
55SSLv3, TLSv1, TLSv1.1 and TLSv1.2 protocols.
56
57If the cipher list does not contain any SSLv2 ciphersuites (the default
58cipher list does not) or extensions are required (for example server name)
59a client will send out TLSv1 client hello messages including extensions and
60will indicate that it also understands TLSv1.1, TLSv1.2 and permits a
61fallback to SSLv3. A server will support SSLv3, TLSv1, TLSv1.1 and TLSv1.2
62protocols. This is the best choice when compatibility is a concern.
63
64If any SSLv2 ciphersuites are included in the cipher list and no extensions
65are required then SSLv2 compatible client hellos will be used by clients and
66SSLv2 will be accepted by servers. This is B<not> recommended due to the
67insecurity of SSLv2 and the limited nature of the SSLv2 client hello
68prohibiting the use of extensions.
69
70=back
71
72The list of protocols available can later be limited using the SSL_OP_NO_SSLv2,
73SSL_OP_NO_SSLv3, SSL_OP_NO_TLSv1, SSL_OP_NO_TLSv1_1 and SSL_OP_NO_TLSv1_2
74options of the SSL_CTX_set_options() or SSL_set_options() functions.
75Using these options it is possible to choose e.g. SSLv23_server_method() and
76be able to negotiate with all possible clients, but to only allow newer
77protocols like TLSv1, TLSv1.1 or TLS v1.2.
78
79Applications which never want to support SSLv2 (even is the cipher string
80is configured to use SSLv2 ciphersuites) can set SSL_OP_NO_SSLv2.
81
82SSL_CTX_new() initializes the list of ciphers, the session cache setting,
83the callbacks, the keys and certificates and the options to its default
84values.
85
86=head1 RETURN VALUES
87
88The following return values can occur:
89
90=over 4
91
92=item NULL
93
94The creation of a new SSL_CTX object failed. Check the error stack to
95find out the reason.
96
97=item Pointer to an SSL_CTX object
98
99The return value points to an allocated SSL_CTX object.
100
101=back
102
103=head1 SEE ALSO
104
105L<SSL_CTX_free(3)|SSL_CTX_free(3)>, L<SSL_accept(3)|SSL_accept(3)>,
106L<ssl(3)|ssl(3)>,  L<SSL_set_connect_state(3)|SSL_set_connect_state(3)>
107
108=cut
109