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=pod
=head1 NAME
SSL_CTX_new, 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, SSLv23_method, SSLv23_server_method, SSLv23_client_method - create a new SSL_CTX object as framework for TLS/SSL enabled functions
=head1 SYNOPSIS
#include <openssl/ssl.h>
SSL_CTX *SSL_CTX_new(const SSL_METHOD *method);
=head1 DESCRIPTION
SSL_CTX_new() creates a new B<SSL_CTX> object as framework to establish
TLS/SSL enabled connections.
=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 SSLv3_method(void), SSLv3_server_method(void), SSLv3_client_method(void)
A TLS/SSL connection established with these methods will only understand the
SSLv3 protocol. A client will send out SSLv3 client hello messages
and will indicate that it only understands SSLv3. A server will only understand
SSLv3 client hello messages. This especially means, that it will
not understand SSLv2 client hello messages which are widely used for
compatibility reasons, see SSLv23_*_method().
=item TLSv1_method(void), TLSv1_server_method(void), TLSv1_client_method(void)
A TLS/SSL connection established with these methods will only understand the
TLSv1 protocol. A client will send out TLSv1 client hello messages
and will indicate that it only understands TLSv1. A server will only understand
TLSv1 client hello messages. This especially means, that it will
not understand SSLv2 client hello messages which are widely used for
compatibility reasons, see SSLv23_*_method(). It will also not understand
SSLv3 client hello messages.
=item TLSv1_1_method(void), TLSv1_1_server_method(void), TLSv1_1_client_method(void)
A TLS/SSL connection established with these methods will only understand the
TLSv1.1 protocol. A client will send out TLSv1.1 client hello messages
and will indicate that it only understands TLSv1.1. A server will only
understand TLSv1.1 client hello messages. This especially means, that it will
not understand SSLv2 client hello messages which are widely used for
compatibility reasons, see SSLv23_*_method(). It will also not understand
SSLv3 client hello messages.
=item SSLv23_method(void), SSLv23_server_method(void), SSLv23_client_method(void)
A TLS/SSL connection established with these methods may understand the
SSLv3, TLSv1, TLSv1.1 and TLSv1.2 protocols.
If extensions are required (for example server name)
a client will send out TLSv1 client hello messages including extensions and
will indicate that it also understands TLSv1.1, TLSv1.2 and permits a
fallback to SSLv3. A server will support SSLv3, TLSv1, TLSv1.1 and TLSv1.2
protocols. This is the best choice when compatibility is a concern.
=back
The list of protocols available can later be limited using the
SSL_OP_NO_SSLv3, SSL_OP_NO_TLSv1, SSL_OP_NO_TLSv1_1 and SSL_OP_NO_TLSv1_2
options of the SSL_CTX_set_options() or SSL_set_options() functions.
Using these options it is possible to choose e.g. SSLv23_server_method() and
be able to negotiate with all possible clients, but to only allow newer
protocols like TLSv1, TLSv1.1 or TLS v1.2.
Applications which never want to support SSLv3 can set SSL_OP_NO_SSLv3.
SSL_CTX_new() initializes the list of ciphers, the session cache setting,
the callbacks, the keys and certificates and the options to its default
values.
=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.
=back
=head1 HISTORY
SSLv2_method, SSLv2_server_method and SSLv2_client_method where removed in
OpenSSL 1.1.0.
=head1 SEE ALSO
L<SSL_CTX_free(3)|SSL_CTX_free(3)>, L<SSL_accept(3)|SSL_accept(3)>,
L<ssl(3)|ssl(3)>, L<SSL_set_connect_state(3)|SSL_set_connect_state(3)>
=cut
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