6d02baf6ab
Update protocols supported and note that SSLv2 is effectively disabled by default. PR#3184 (cherry picked from commit 1b13a4f38dfc385d5e776f6b3e06c5795874cf9b)
108 lines
4 KiB
Text
108 lines
4 KiB
Text
=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(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 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 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 SSLv2,
|
|
SSLv3, TLSv1, TLSv1.1 and TLSv1.2 protocols.
|
|
|
|
If the cipher list does not contain any SSLv2 ciphersuites (the default
|
|
cipher list does not) or 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.
|
|
|
|
If any SSLv2 ciphersuites are included in the cipher list and no extensions
|
|
are required then SSLv2 compatible client hellos will be used by clients and
|
|
SSLv2 will be accepted by servers. This is B<not> recommended due to the
|
|
insecurity of SSLv2 and the limited nature of the SSLv2 client hello
|
|
prohibiting the use of extensions.
|
|
|
|
=back
|
|
|
|
The list of protocols available can later be limited using the SSL_OP_NO_SSLv2,
|
|
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 SSLv2 (even is the cipher string
|
|
is configured to use SSLv2 ciphersuites) can set SSL_OP_NO_SSLv2.
|
|
|
|
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
|