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=pod
=head1 NAME
SSL_set_num_tickets,
SSL_get_num_tickets,
SSL_CTX_set_num_tickets,
SSL_CTX_get_num_tickets,
SSL_new_session_ticket
- control the number of TLSv1.3 session tickets that are issued
=head1 SYNOPSIS
#include <openssl/ssl.h>
int SSL_set_num_tickets(SSL *s, size_t num_tickets);
size_t SSL_get_num_tickets(SSL *s);
int SSL_CTX_set_num_tickets(SSL_CTX *ctx, size_t num_tickets);
size_t SSL_CTX_get_num_tickets(SSL_CTX *ctx);
int SSL_new_session_ticket(SSL *s);
=head1 DESCRIPTION
SSL_CTX_set_num_tickets() and SSL_set_num_tickets() can be called for a server
application and set the number of TLSv1.3 session tickets that will be sent to
the client after a full handshake. Set the desired value (which could be 0) in
the B<num_tickets> argument. Typically these functions should be called before
the start of the handshake.
The default number of tickets is 2; the default number of tickets sent following
a resumption handshake is 1 but this cannot be changed using these functions.
The number of tickets following a resumption handshake can be reduced to 0 using
custom session ticket callbacks (see L<SSL_CTX_set_session_ticket_cb(3)>).
Tickets are also issued on receipt of a post-handshake certificate from the
client following a request by the server using
L<SSL_verify_client_post_handshake(3)>. These new tickets will be associated
with the updated client identity (i.e. including their certificate and
verification status). The number of tickets issued will normally be the same as
was used for the initial handshake. If the initial handshake was a full
handshake then SSL_set_num_tickets() can be called again prior to calling
SSL_verify_client_post_handshake() to update the number of tickets that will be
sent.
To issue tickets after other events (such as application-layer changes),
SSL_new_session_ticket() is used by a server application to request that a new
ticket be sent when it is safe to do so. New tickets are only allowed to be
sent in this manner after the initial handshake has completed, and only for TLS
1.3 connections. The ticket generation and transmission are delayed until the
server is starting a new write operation, so that it is bundled with other
application data being written and properly aligned to a record boundary.
SSL_new_session_ticket() can be called more than once to request additional
tickets be sent; all such requests are queued and written together when it is
safe to do so. Note that a successful return from SSL_new_session_ticket()
indicates only that the request to send a ticket was processed, not that the
ticket itself was sent. To be notified when the ticket itself is sent, a
new-session callback can be registered with L<SSL_CTX_sess_set_new_cb(3)> that
will be invoked as the ticket or tickets are generated.
SSL_CTX_get_num_tickets() and SSL_get_num_tickets() return the number of
tickets set by a previous call to SSL_CTX_set_num_tickets() or
SSL_set_num_tickets(), or 2 if no such call has been made.
=head1 RETURN VALUES
SSL_CTX_set_num_tickets(), SSL_set_num_tickets(), and
SSL_new_session_ticket() return 1 on success or 0 on failure.
SSL_CTX_get_num_tickets() and SSL_get_num_tickets() return the number of tickets
that have been previously set.
=head1 SEE ALSO
L<ssl(7)>
=head1 HISTORY
SSL_new_session_ticket() was added in OpenSSL 3.0.0.
SSL_set_num_tickets(), SSL_get_num_tickets(), SSL_CTX_set_num_tickets(), and
SSL_CTX_get_num_tickets() were added in OpenSSL 1.1.1.
=head1 COPYRIGHT
Copyright 2018-2020 The OpenSSL Project Authors. All Rights Reserved.
Licensed under the Apache License 2.0 (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
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