Add documentation for SSL_key_update() and SSL_get_key_update_type()

=pod

=head1 NAME

SSL_key_update,

SSL_get_key_update_type,

SSL_renegotiate,

SSL_renegotiate_abbreviated,

SSL_renegotiate_pending

- initiate and obtain information about updating connection keys

=head1 SYNOPSIS

 #include <openssl/ssl.h>

 /* TLSv1.3 KeyUpdate message types */

 typedef enum {

     /* -1 used so that this is an invalid value for the on-the-wire protocol */

     SSL_KEY_UPDATE_NONE = -1,

     /* Values as defined for the on-the-wire protocol */

     SSL_KEY_UPDATE_NOT_REQUESTED = 0,

     SSL_KEY_UPDATE_REQUESTED = 1

 } SSL_KEY_UPDATE;

 int SSL_key_update(SSL *s, SSL_KEY_UPDATE updatetype);

 SSL_KEY_UPDATE SSL_get_key_update_type(SSL *s);

 int SSL_renegotiate(SSL *s);

 int SSL_renegotiate_abbreviated(SSL *s);

 int SSL_renegotiate_pending(SSL *s);

=head1 DESCRIPTION

SSL_key_update() schedules an update of the keys for the current TLS connection.

If the B<updatetype> parameter is set to B<SSL_KEY_UPDATE_NOT_REQUESTED> then

the sending keys for this connection will be updated and the peer will be

informed of the change. If the B<updatetype> parameter is set to

B<SSL_KEY_UPDATE_REQUESTED> then the sending keys for this connection will be

updated and the peer will be informed of the change along with a request for the

peer to additionally update its sending keys. It is an error if B<updatetype> is

set to B<SSL_KEY_UPDATE_NONE>.

SSL_key_update() must only be called after the initial handshake has been

completed and TLSv1.3 has been negotiated. The key update will not take place

until the next time an IO operation such as SSL_read_ex() or SSL_write_ex()

takes place on the connection. Alternatively SSL_do_handshake() can be called to

force the update to take place immediately.

SSL_get_key_update_type() can be used to determine whether a key update

operation has been scheduled but not yet performed. The type of the pending key

update operation will be returned if there is one, or SSL_KEY_UPDATE_NONE

otherwise.

SSL_renegotiate() and SSL_renegotiate_abbreviated() should only be called for

connections that have negotiated TLSv1.2 or less. Calling them on any other

connection will result in an error.

When called from the client side, SSL_renegotiate() schedules a completely new

handshake over an existing SSL/TLS connection. The next time an IO operation

such as SSL_read_ex() or SSL_write_ex() takes place on the connection a check

will be performed to confirm that it is a suitable time to start a

renegotiation. If so, then it will be initiated immediately. OpenSSL will not

attempt to resume any session associated with the connection in the new

handshake.

When called from the client side, SSL_renegotiate_abbreviated() works in the

same was as SSL_renegotiate() except that OpenSSL will attempt to resume the

session associated with the current connection in the new handshake.

When called from the server side, SSL_renegotiate() and

SSL_renegotiate_abbreviated() behave identically. They both schedule a request

for a new handshake to be sent to the client. The next time an IO operation is

performed then the same checks as on the client side are performed and then, if

appropriate, the request is sent. The client may or may not respond with a new

handshake and it may or may not attempt to resume an existing session. If

a new handshake is started then this will be handled transparently by calling

any OpenSSL IO function.

If an OpenSSL client receives a renegotiation request from a server then again

this will be handled transparently through calling any OpenSSL IO function. For

a TLS connection the client will attempt to resume the current session in the

new handshake. For historical reasons, DTLS clients will not attempt to resume

the session in the new handshake.

The SSL_renegotiate_pending() function returns 1 if a renegotiation or

rengotiation request has been scheduled but not yet acted on, or 0 otherwise.

=head1 RETURN VALUES

SSL_key_update(), SSL_renegotiate() and SSL_renegotiate_abbreviated() return 1

on success or 0 on error.

SSL_get_key_update_type() returns the update type of the pending key update

operation or SSL_KEY_UPDATE_NONE if there is none.

SSL_renegotiate_pending() returns 1 if a renegotiation or rengotiation request

has been scheduled but not yet acted on, or 0 otherwise.

=head1 SEE ALSO

L<ssl(7)>, L<SSL_read_ex(3)>,

L<SSL_write_ex(3)>,

L<SSL_do_handshake(3)>

=head1 HISTORY

The SSL_key_update() and SSL_get_key_update_type() functions were added in

OpenSSL 1.1.1.

=head1 COPYRIGHT

Copyright 2017 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the OpenSSL license (the "License").  You may not use

this file except in compliance with the License.  You can obtain a copy

in the file LICENSE in the source distribution or at

L<https://www.openssl.org/source/license.html>.

=cut

=item void (*B<SSL_get_info_callback>(const SSL *ssl);)()

=item SSL_KEY_UPDATE B<SSL_get_key_update_type>(SSL *s);

=item STACK *B<SSL_get_peer_cert_chain>(const SSL *ssl);

=item X509 *B<SSL_get_peer_certificate>(const SSL *ssl);

=item int B<SSL_is_init_finished>(SSL *ssl);

=item int B<SSL_key_update>(SSL *s, SSL_KEY_UPDATE updatetype);

=item STACK *B<SSL_load_client_CA_file>(const char *file);

=item SSL *B<SSL_new>(SSL_CTX *ctx);