=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 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.

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.

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 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