1=pod
2
3=head1 NAME
4
5SSL_set_num_tickets,
6SSL_get_num_tickets,
7SSL_CTX_set_num_tickets,
8SSL_CTX_get_num_tickets,
9SSL_new_session_ticket
10- control the number of TLSv1.3 session tickets that are issued
11
12=head1 SYNOPSIS
13
14 #include <openssl/ssl.h>
15
16 int SSL_set_num_tickets(SSL *s, size_t num_tickets);
17 size_t SSL_get_num_tickets(const SSL *s);
18 int SSL_CTX_set_num_tickets(SSL_CTX *ctx, size_t num_tickets);
19 size_t SSL_CTX_get_num_tickets(const SSL_CTX *ctx);
20 int SSL_new_session_ticket(SSL *s);
21
22=head1 DESCRIPTION
23
24SSL_CTX_set_num_tickets() and SSL_set_num_tickets() can be called for a server
25application and set the number of TLSv1.3 session tickets that will be sent to
26the client after a full handshake. Set the desired value (which could be 0) in
27the B<num_tickets> argument. Typically these functions should be called before
28the start of the handshake.
29
30The default number of tickets is 2. Following a resumption the number of tickets
31issued will never be more than 1 regardless of the value set via
32SSL_set_num_tickets() or SSL_CTX_set_num_tickets(). If B<num_tickets> is set to
330 then no tickets will be issued for either a normal connection or a resumption.
34
35Tickets are also issued on receipt of a post-handshake certificate from the
36client following a request by the server using
37L<SSL_verify_client_post_handshake(3)>. These new tickets will be associated
38with the updated client identity (i.e. including their certificate and
39verification status). The number of tickets issued will normally be the same as
40was used for the initial handshake. If the initial handshake was a full
41handshake then SSL_set_num_tickets() can be called again prior to calling
42SSL_verify_client_post_handshake() to update the number of tickets that will be
43sent.
44
45To issue tickets after other events (such as application-layer changes),
46SSL_new_session_ticket() is used by a server application to request that a new
47ticket be sent when it is safe to do so.  New tickets are only allowed to be
48sent in this manner after the initial handshake has completed, and only for
49TLS 1.3 connections.  By default, the ticket generation and transmission are
50delayed until the server is starting a new write operation, so that it is
51bundled with other application data being written and properly aligned to a
52record boundary.  If the connection was at a record boundary when
53SSL_new_session_ticket() was called, the ticket can be sent immediately
54(without waiting for the next application write) by calling
55SSL_do_handshake().  SSL_new_session_ticket() can be called more than once to
56request additional tickets be sent; all such requests are queued and written
57together when it is safe to do so and triggered by SSL_write() or
58SSL_do_handshake().  Note that a successful return from
59SSL_new_session_ticket() indicates only that the request to send a ticket was
60processed, not that the ticket itself was sent.  To be notified when the
61ticket itself is sent, a new-session callback can be registered with
62L<SSL_CTX_sess_set_new_cb(3)> that will be invoked as the ticket or tickets
63are generated.
64
65SSL_CTX_get_num_tickets() and SSL_get_num_tickets() return the number of
66tickets set by a previous call to SSL_CTX_set_num_tickets() or
67SSL_set_num_tickets(), or 2 if no such call has been made.
68
69=head1 RETURN VALUES
70
71SSL_CTX_set_num_tickets(), SSL_set_num_tickets(), and
72SSL_new_session_ticket() return 1 on success or 0 on failure.
73
74SSL_CTX_get_num_tickets() and SSL_get_num_tickets() return the number of tickets
75that have been previously set.
76
77=head1 SEE ALSO
78
79L<ssl(7)>
80
81=head1 HISTORY
82
83SSL_new_session_ticket() was added in OpenSSL 3.0.0.
84SSL_set_num_tickets(), SSL_get_num_tickets(), SSL_CTX_set_num_tickets(), and
85SSL_CTX_get_num_tickets() were added in OpenSSL 1.1.1.
86
87=head1 COPYRIGHT
88
89Copyright 2018-2021 The OpenSSL Project Authors. All Rights Reserved.
90
91Licensed under the Apache License 2.0 (the "License").  You may not use
92this file except in compliance with the License.  You can obtain a copy
93in the file LICENSE in the source distribution or at
94L<https://www.openssl.org/source/license.html>.
95
96=cut
97