Initial Commit

openssl-1.0.2f/doc/ssl/SSL_CTX_new.pod

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+=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