=pod

=head1 NAME

SSL_CTX_new,
SSLv23_method, SSLv23_server_method, SSLv23_client_method,
TLSv1_2_method, TLSv1_2_server_method, TLSv1_2_client_method,
TLSv1_1_method, TLSv1_1_server_method, TLSv1_1_client_method,
TLSv1_method, TLSv1_server_method, TLSv1_client_method,
SSLv3_method, SSLv3_server_method, SSLv3_client_method,
SSLv2_method, SSLv2_server_method, SSLv2_client_method,
DTLSv1_method, DTLSv1_server_method, DTLSv1_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);
 const SSL_METHOD *SSLv23_method(void);
 const SSL_METHOD *SSLv23_server_method(void);
 const SSL_METHOD *SSLv23_client_method(void);
 const SSL_METHOD *TLSv1_2_method(void);
 const SSL_METHOD *TLSv1_2_server_method(void);
 const SSL_METHOD *TLSv1_2_client_method(void);
 const SSL_METHOD *TLSv1_1_method(void);
 const SSL_METHOD *TLSv1_1_server_method(void);
 const SSL_METHOD *TLSv1_1_client_method(void);
 const SSL_METHOD *TLSv1_method(void);
 const SSL_METHOD *TLSv1_server_method(void);
 const SSL_METHOD *TLSv1_client_method(void);
 #ifndef OPENSSL_NO_SSL3_METHOD
 const SSL_METHOD *SSLv3_method(void);
 const SSL_METHOD *SSLv3_server_method(void);
 const SSL_METHOD *SSLv3_client_method(void);
 #endif
 #ifndef OPENSSL_NO_SSL2
 const SSL_METHOD *SSLv2_method(void);
 const SSL_METHOD *SSLv2_server_method(void);
 const SSL_METHOD *SSLv2_client_method(void);
 #endif

 const SSL_METHOD *DTLSv1_method(void);
 const SSL_METHOD *DTLSv1_server_method(void);
 const SSL_METHOD *DTLSv1_client_method(void);

=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 SSLv23_method(), SSLv23_server_method(), SSLv23_client_method()

These are the general-purpose I<version-flexible> SSL/TLS methods.
The actual protocol version used will be negotiated to the highest version
mutually supported by the client and the server.
The supported protocols are SSLv2, SSLv3, TLSv1, TLSv1.1 and TLSv1.2.
Most applications should use these method, and avoid the version specific
methods described below.

The list of protocols available can be further limited using the
B<SSL_OP_NO_SSLv2>, B<SSL_OP_NO_SSLv3>, B<SSL_OP_NO_TLSv1>,
B<SSL_OP_NO_TLSv1_1> and B<SSL_OP_NO_TLSv1_2> options of the
L<SSL_CTX_set_options(3)> or L<SSL_set_options(3)> functions.
Clients should avoid creating "holes" in the set of protocols they support,
when disabling a protocol, make sure that you also disable either all previous
or all subsequent protocol versions.
In clients, when a protocol version is disabled without disabling I<all>
previous protocol versions, the effect is to also disable all subsequent
protocol versions.

The SSLv2 and SSLv3 protocols are deprecated and should generally not be used.
Applications should typically use L<SSL_CTX_set_options(3)> in combination with
the B<SSL_OP_NO_SSLv3> flag to disable negotiation of SSLv3 via the above
I<version-flexible> SSL/TLS methods.
The B<SSL_OP_NO_SSLv2> option is set by default, and would need to be cleared
via L<SSL_CTX_clear_options(3)> in order to enable negotiation of SSLv2.

=item TLSv1_2_method(), TLSv1_2_server_method(), TLSv1_2_client_method()

A TLS/SSL connection established with these methods will only understand the
TLSv1.2 protocol.  A client will send out TLSv1.2 client hello messages and
will also indicate that it only understand TLSv1.2.  A server will only
understand TLSv1.2 client hello messages.

=item TLSv1_1_method(), TLSv1_1_server_method(), TLSv1_1_client_method()

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 also indicate that it only understand TLSv1.1.  A server will only
understand TLSv1.1 client hello messages.

=item TLSv1_method(), TLSv1_server_method(), TLSv1_client_method()

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.

=item SSLv3_method(), SSLv3_server_method(), SSLv3_client_method()

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.  The SSLv3 protocol is deprecated and should not be
used.

=item SSLv2_method(), SSLv2_server_method(), SSLv2_client_method()

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.  The SSLv2 protocol offers little to no security
and should not be used.
As of OpenSSL 1.0.1s, EXPORT ciphers and 56-bit DES are no longer available
with SSLv2.

=item DTLSv1_method(), DTLSv1_server_method(), DTLSv1_client_method()

These are the version-specific methods for DTLSv1.

=back

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_set_options(3)>, L<SSL_CTX_clear_options(3)>, L<SSL_set_options(3)>,
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
