1=pod
2
3=head1 NAME
4
5SSL_CTX_set_session_ticket_cb,
6SSL_SESSION_get0_ticket_appdata,
7SSL_SESSION_set1_ticket_appdata,
8SSL_CTX_generate_session_ticket_fn,
9SSL_CTX_decrypt_session_ticket_fn - manage session ticket application data
10
11=head1 SYNOPSIS
12
13 #include <openssl/ssl.h>
14
15 typedef int (*SSL_CTX_generate_session_ticket_fn)(SSL *s, void *arg);
16 typedef SSL_TICKET_RETURN (*SSL_CTX_decrypt_session_ticket_fn)(SSL *s, SSL_SESSION *ss,
17                                                                const unsigned char *keyname,
18                                                                size_t keyname_len,
19                                                                SSL_TICKET_STATUS status,
20                                                                void *arg);
21 int SSL_CTX_set_session_ticket_cb(SSL_CTX *ctx,
22                                   SSL_CTX_generate_session_ticket_fn gen_cb,
23                                   SSL_CTX_decrypt_session_ticket_fn dec_cb,
24                                   void *arg);
25 int SSL_SESSION_set1_ticket_appdata(SSL_SESSION *ss, const void *data, size_t len);
26 int SSL_SESSION_get0_ticket_appdata(SSL_SESSION *ss, void **data, size_t *len);
27
28=head1 DESCRIPTION
29
30SSL_CTX_set_set_session_ticket_cb() sets the application callbacks B<gen_cb>
31and B<dec_cb> that are used by a server to set and get application data stored
32with a session, and placed into a session ticket. Either callback function may
33be set to NULL. The value of B<arg> is passed to the callbacks.
34
35B<gen_cb> is the application defined callback invoked when a session ticket is
36about to be created. The application can call SSL_SESSION_set1_ticket_appdata()
37at this time to add application data to the session ticket. The value of B<arg>
38is the same as that given to SSL_CTX_set_session_ticket_cb(). The B<gen_cb>
39callback is defined as type B<SSL_CTX_generate_session_ticket_fn>.
40
41B<dec_cb> is the application defined callback invoked after session ticket
42decryption has been attempted and any session ticket application data is
43available. If ticket decryption was successful then the B<ss> argument contains
44the session data. The B<keyname> and B<keyname_len> arguments identify the key
45used to decrypt the session ticket. The B<status> argument is the result of the
46ticket decryption. See the L</NOTES> section below for further details. The value
47of B<arg> is the same as that given to SSL_CTX_set_session_ticket_cb(). The
48B<dec_cb> callback is defined as type B<SSL_CTX_decrypt_session_ticket_fn>.
49
50SSL_SESSION_set1_ticket_appdata() sets the application data specified by
51B<data> and B<len> into B<ss> which is then placed into any generated session
52tickets. It can be called at any time before a session ticket is created to
53update the data placed into the session ticket. However, given that sessions
54and tickets are created by the handshake, the B<gen_cb> is provided to notify
55the application that a session ticket is about to be generated.
56
57SSL_SESSION_get0_ticket_appdata() assigns B<data> to the session ticket
58application data and assigns B<len> to the length of the session ticket
59application data from B<ss>. The application data can be set via
60SSL_SESSION_set1_ticket_appdata() or by a session ticket. NULL will be assigned
61to B<data> and 0 will be assigned to B<len> if there is no session ticket
62application data. SSL_SESSION_get0_ticket_appdata() can be called any time
63after a session has been created. The B<dec_cb> is provided to notify the
64application that a session ticket has just been decrypted.
65
66=head1 NOTES
67
68When the B<dec_cb> callback is invoked, the SSL_SESSION B<ss> has not yet been
69assigned to the SSL B<s>. The B<status> indicates the result of the ticket
70decryption. The callback must check the B<status> value before performing any
71action, as it is called even if ticket decryption fails.
72
73The B<keyname> and B<keyname_len> arguments to B<dec_cb> may be used to identify
74the key that was used to encrypt the session ticket.
75
76The B<status> argument can be any of these values:
77
78=over 4
79
80=item SSL_TICKET_EMPTY
81
82Empty ticket present. No ticket data will be used and a new ticket should be
83sent to the client. This only occurs in TLSv1.2 or below. In TLSv1.3 it is not
84valid for a client to send an empty ticket.
85
86=item SSL_TICKET_NO_DECRYPT
87
88The ticket couldn't be decrypted. No ticket data will be used and a new ticket
89should be sent to the client.
90
91=item SSL_TICKET_SUCCESS
92
93A ticket was successfully decrypted, any session ticket application data should
94be available. A new ticket should not be sent to the client.
95
96=item SSL_TICKET_SUCCESS_RENEW
97
98Same as B<SSL_TICKET_SUCCESS>, but a new ticket should be sent to the client.
99
100=back
101
102The return value can be any of these values:
103
104=over 4
105
106=item SSL_TICKET_RETURN_ABORT
107
108The handshake should be aborted, either because of an error or because of some
109policy. Note that in TLSv1.3 a client may send more than one ticket in a single
110handshake. Therefore, just because one ticket is unacceptable it does not mean
111that all of them are. For this reason this option should be used with caution.
112
113=item SSL_TICKET_RETURN_IGNORE
114
115Do not use a ticket (if one was available). Do not send a renewed ticket to the
116client.
117
118=item SSL_TICKET_RETURN_IGNORE_RENEW
119
120Do not use a ticket (if one was available). Send a renewed ticket to the client.
121
122If the callback does not wish to change the default ticket behaviour then it
123should return this value if B<status> is B<SSL_TICKET_EMPTY> or
124B<SSL_TICKET_NO_DECRYPT>.
125
126=item SSL_TICKET_RETURN_USE
127
128Use the ticket. Do not send a renewed ticket to the client. It is an error for
129the callback to return this value if B<status> has a value other than
130B<SSL_TICKET_SUCCESS> or B<SSL_TICKET_SUCCESS_RENEW>.
131
132If the callback does not wish to change the default ticket behaviour then it
133should return this value if B<status> is B<SSL_TICKET_SUCCESS>.
134
135=item SSL_TICKET_RETURN_USE_RENEW
136
137Use the ticket. Send a renewed ticket to the client. It is an error for the
138callback to return this value if B<status> has a value other than
139B<SSL_TICKET_SUCCESS> or B<SSL_TICKET_SUCCESS_RENEW>.
140
141If the callback does not wish to change the default ticket behaviour then it
142should return this value if B<status> is B<SSL_TICKET_SUCCESS_RENEW>.
143
144=back
145
146If B<status> has the value B<SSL_TICKET_EMPTY> or B<SSL_TICKET_NO_DECRYPT> then
147no session data will be available and the callback must not use the B<ss>
148argument. If B<status> has the value B<SSL_TICKET_SUCCESS> or
149B<SSL_TICKET_SUCCESS_RENEW> then the application can call
150SSL_SESSION_get0_ticket_appdata() using the session provided in the B<ss>
151argument to retrieve the application data.
152
153When the B<gen_cb> callback is invoked, the SSL_get_session() function can be
154used to retrieve the SSL_SESSION for SSL_SESSION_set1_ticket_appdata().
155
156By default, in TLSv1.2 and below, a new session ticket is not issued on a
157successful resumption and therefore B<gen_cb> will not be called. In TLSv1.3 the
158default behaviour is to always issue a new ticket on resumption. In both cases
159this behaviour can be changed if a ticket key callback is in use (see
160L<SSL_CTX_set_tlsext_ticket_key_cb(3)>).
161
162=head1 RETURN VALUES
163
164The SSL_CTX_set_session_ticket_cb(), SSL_SESSION_set1_ticket_appdata() and
165SSL_SESSION_get0_ticket_appdata() functions return 1 on success and 0 on
166failure.
167
168The B<gen_cb> callback must return 1 to continue the connection. A return of 0
169will terminate the connection with an INTERNAL_ERROR alert.
170
171The B<dec_cb> callback must return a value as described in L</NOTES> above.
172
173=head1 SEE ALSO
174
175L<ssl(7)>,
176L<SSL_get_session(3)>
177
178=head1 HISTORY
179
180The SSL_CTX_set_session_ticket_cb(), SSL_SESSION_set1_ticket_appdata()
181and SSL_SESSION_get_ticket_appdata() functions were added in OpenSSL 1.1.1.
182
183=head1 COPYRIGHT
184
185Copyright 2017-2020 The OpenSSL Project Authors. All Rights Reserved.
186
187Licensed under the Apache License 2.0 (the "License").  You may not use
188this file except in compliance with the License.  You can obtain a copy
189in the file LICENSE in the source distribution or at
190L<https://www.openssl.org/source/license.html>.
191
192=cut
193