Provided by: libssl-doc_3.0.13-0ubuntu3.6_all 
NAME
SSL_CTX_set_session_ticket_cb, SSL_SESSION_get0_ticket_appdata, SSL_SESSION_set1_ticket_appdata,
SSL_CTX_generate_session_ticket_fn, SSL_CTX_decrypt_session_ticket_fn - manage session ticket application
data
SYNOPSIS
#include <openssl/ssl.h>
typedef int (*SSL_CTX_generate_session_ticket_fn)(SSL *s, void *arg);
typedef SSL_TICKET_RETURN (*SSL_CTX_decrypt_session_ticket_fn)(SSL *s, SSL_SESSION *ss,
const unsigned char *keyname,
size_t keyname_len,
SSL_TICKET_STATUS status,
void *arg);
int SSL_CTX_set_session_ticket_cb(SSL_CTX *ctx,
SSL_CTX_generate_session_ticket_fn gen_cb,
SSL_CTX_decrypt_session_ticket_fn dec_cb,
void *arg);
int SSL_SESSION_set1_ticket_appdata(SSL_SESSION *ss, const void *data, size_t len);
int SSL_SESSION_get0_ticket_appdata(SSL_SESSION *ss, void **data, size_t *len);
DESCRIPTION
SSL_CTX_set_set_session_ticket_cb() sets the application callbacks gen_cb and dec_cb that are used by a
server to set and get application data stored with a session, and placed into a session ticket. Either
callback function may be set to NULL. The value of arg is passed to the callbacks.
gen_cb is the application defined callback invoked when a session ticket is about to be created. The
application can call SSL_SESSION_set1_ticket_appdata() at this time to add application data to the
session ticket. The value of arg is the same as that given to SSL_CTX_set_session_ticket_cb(). The gen_cb
callback is defined as type SSL_CTX_generate_session_ticket_fn.
dec_cb is the application defined callback invoked after session ticket decryption has been attempted and
any session ticket application data is available. If ticket decryption was successful then the ss
argument contains the session data. The keyname and keyname_len arguments identify the key used to
decrypt the session ticket. The status argument is the result of the ticket decryption. See the "NOTES"
section below for further details. The value of arg is the same as that given to
SSL_CTX_set_session_ticket_cb(). The dec_cb callback is defined as type
SSL_CTX_decrypt_session_ticket_fn.
SSL_SESSION_set1_ticket_appdata() sets the application data specified by data and len into ss which is
then placed into any generated session tickets. It can be called at any time before a session ticket is
created to update the data placed into the session ticket. However, given that sessions and tickets are
created by the handshake, the gen_cb is provided to notify the application that a session ticket is about
to be generated.
SSL_SESSION_get0_ticket_appdata() assigns data to the session ticket application data and assigns len to
the length of the session ticket application data from ss. The application data can be set via
SSL_SESSION_set1_ticket_appdata() or by a session ticket. NULL will be assigned to data and 0 will be
assigned to len if there is no session ticket application data. SSL_SESSION_get0_ticket_appdata() can be
called any time after a session has been created. The dec_cb is provided to notify the application that a
session ticket has just been decrypted.
NOTES
When the dec_cb callback is invoked, the SSL_SESSION ss has not yet been assigned to the SSL s. The
status indicates the result of the ticket decryption. The callback must check the status value before
performing any action, as it is called even if ticket decryption fails.
The keyname and keyname_len arguments to dec_cb may be used to identify the key that was used to encrypt
the session ticket.
The status argument can be any of these values:
SSL_TICKET_EMPTY
Empty ticket present. No ticket data will be used and a new ticket should be sent to the client. This
only occurs in TLSv1.2 or below. In TLSv1.3 it is not valid for a client to send an empty ticket.
SSL_TICKET_NO_DECRYPT
The ticket couldn't be decrypted. No ticket data will be used and a new ticket should be sent to the
client.
SSL_TICKET_SUCCESS
A ticket was successfully decrypted, any session ticket application data should be available. A new
ticket should not be sent to the client.
SSL_TICKET_SUCCESS_RENEW
Same as SSL_TICKET_SUCCESS, but a new ticket should be sent to the client.
The return value can be any of these values:
SSL_TICKET_RETURN_ABORT
The handshake should be aborted, either because of an error or because of some policy. Note that in
TLSv1.3 a client may send more than one ticket in a single handshake. Therefore, just because one
ticket is unacceptable it does not mean that all of them are. For this reason this option should be
used with caution.
SSL_TICKET_RETURN_IGNORE
Do not use a ticket (if one was available). Do not send a renewed ticket to the client.
SSL_TICKET_RETURN_IGNORE_RENEW
Do not use a ticket (if one was available). Send a renewed ticket to the client.
If the callback does not wish to change the default ticket behaviour then it should return this value
if status is SSL_TICKET_EMPTY or SSL_TICKET_NO_DECRYPT.
SSL_TICKET_RETURN_USE
Use the ticket. Do not send a renewed ticket to the client. It is an error for the callback to return
this value if status has a value other than SSL_TICKET_SUCCESS or SSL_TICKET_SUCCESS_RENEW.
If the callback does not wish to change the default ticket behaviour then it should return this value
if status is SSL_TICKET_SUCCESS.
SSL_TICKET_RETURN_USE_RENEW
Use the ticket. Send a renewed ticket to the client. It is an error for the callback to return this
value if status has a value other than SSL_TICKET_SUCCESS or SSL_TICKET_SUCCESS_RENEW.
If the callback does not wish to change the default ticket behaviour then it should return this value
if status is SSL_TICKET_SUCCESS_RENEW.
If status has the value SSL_TICKET_EMPTY or SSL_TICKET_NO_DECRYPT then no session data will be available
and the callback must not use the ss argument. If status has the value SSL_TICKET_SUCCESS or
SSL_TICKET_SUCCESS_RENEW then the application can call SSL_SESSION_get0_ticket_appdata() using the
session provided in the ss argument to retrieve the application data.
When the gen_cb callback is invoked, the SSL_get_session() function can be used to retrieve the
SSL_SESSION for SSL_SESSION_set1_ticket_appdata().
By default, in TLSv1.2 and below, a new session ticket is not issued on a successful resumption and
therefore gen_cb will not be called. In TLSv1.3 the default behaviour is to always issue a new ticket on
resumption. In both cases this behaviour can be changed if a ticket key callback is in use (see
SSL_CTX_set_tlsext_ticket_key_cb(3)).
RETURN VALUES
The SSL_CTX_set_session_ticket_cb(), SSL_SESSION_set1_ticket_appdata() and
SSL_SESSION_get0_ticket_appdata() functions return 1 on success and 0 on failure.
The gen_cb callback must return 1 to continue the connection. A return of 0 will terminate the connection
with an INTERNAL_ERROR alert.
The dec_cb callback must return a value as described in "NOTES" above.
SEE ALSO
ssl(7), SSL_get_session(3)
HISTORY
The SSL_CTX_set_session_ticket_cb(), SSL_SESSION_set1_ticket_appdata() and
SSL_SESSION_get_ticket_appdata() functions were added in OpenSSL 1.1.1.
COPYRIGHT
Copyright 2017-2020 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
<https://www.openssl.org/source/license.html>.
3.0.13 2025-09-18 SSL_CTX_SET_SESSION_TICKET_CB(3SSL)