=pod

=head1 NAME

SSL_CTX_new - create a new SSL_CTX object as framework for TLS/SSL enabled functions

=head1 SYNOPSIS

 #include <openssl/ssl.h>

 SSL_CTX *SSL_CTX_new(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 SSLv2_method(void), SSLv2_server_method(void), SSLv2_client_method(void)

A TLS/SSL connection established with these methods will only understand
the SSLv2 protocol. A client will send out SSLv2 client hello messages
and will also indicate that it only understand SSLv2. A server will only
understand SSLv2 client hello messages.

=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 and TLSv1 protocol. A client will send out SSLv3 client hello messages
and will indicate that it also understands TLSv1. A server will only understand
SSLv3 and 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().

=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().

=item SSLv23_method(void), SSLv23_server_method(void), SSLv23_client_method(void)

A TLS/SSL connection established with these methods will understand the SSLv2,
SSLv3, and TLSv1 protocol. A client will send out SSLv2 client hello messages
and will indicate that it also understands SSLv3 and TLSv1. A server will
understand SSLv2, SSLv3, and TLSv1 client hello messages. 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_SSLv2,
SSL_OP_NO_SSLv3, SSL_OP_NO_TLSv1 options of the B<SSL_CTX_set_options()> or
B<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 SSLv3 or TLSv1.

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)>

=cut
