| 1 | =pod
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| 2 |
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| 3 | =head1 NAME
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| 4 |
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| 5 | SSL_set_num_tickets,
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| 6 | SSL_get_num_tickets,
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| 7 | SSL_CTX_set_num_tickets,
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| 8 | SSL_CTX_get_num_tickets,
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| 9 | SSL_new_session_ticket
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| 10 | - control the number of TLSv1.3 session tickets that are issued
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| 11 |
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| 12 | =head1 SYNOPSIS
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| 13 |
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| 14 | #include <openssl/ssl.h>
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| 15 |
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| 16 | int SSL_set_num_tickets(SSL *s, size_t num_tickets);
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| 17 | size_t SSL_get_num_tickets(const SSL *s);
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| 18 | int SSL_CTX_set_num_tickets(SSL_CTX *ctx, size_t num_tickets);
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| 19 | size_t SSL_CTX_get_num_tickets(const SSL_CTX *ctx);
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| 20 | int SSL_new_session_ticket(SSL *s);
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| 21 |
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| 22 | =head1 DESCRIPTION
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| 23 |
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| 24 | SSL_CTX_set_num_tickets() and SSL_set_num_tickets() can be called for a server
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| 25 | application and set the number of TLSv1.3 session tickets that will be sent to
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| 26 | the client after a full handshake. Set the desired value (which could be 0) in
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| 27 | the B<num_tickets> argument. Typically these functions should be called before
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| 28 | the start of the handshake.
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| 29 |
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| 30 | The default number of tickets is 2. Following a resumption the number of tickets
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| 31 | issued will never be more than 1 regardless of the value set via
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| 32 | SSL_set_num_tickets() or SSL_CTX_set_num_tickets(). If B<num_tickets> is set to
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| 33 | 0 then no tickets will be issued for either a normal connection or a resumption.
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| 34 |
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| 35 | Tickets are also issued on receipt of a post-handshake certificate from the
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| 36 | client following a request by the server using
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| 37 | L<SSL_verify_client_post_handshake(3)>. These new tickets will be associated
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| 38 | with the updated client identity (i.e. including their certificate and
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| 39 | verification status). The number of tickets issued will normally be the same as
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| 40 | was used for the initial handshake. If the initial handshake was a full
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| 41 | handshake then SSL_set_num_tickets() can be called again prior to calling
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| 42 | SSL_verify_client_post_handshake() to update the number of tickets that will be
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| 43 | sent.
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| 44 |
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| 45 | To issue tickets after other events (such as application-layer changes),
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| 46 | SSL_new_session_ticket() is used by a server application to request that a new
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| 47 | ticket be sent when it is safe to do so. New tickets are only allowed to be
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| 48 | sent in this manner after the initial handshake has completed, and only for
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| 49 | TLS 1.3 connections. By default, the ticket generation and transmission are
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| 50 | delayed until the server is starting a new write operation, so that it is
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| 51 | bundled with other application data being written and properly aligned to a
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| 52 | record boundary. If the connection was at a record boundary when
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| 53 | SSL_new_session_ticket() was called, the ticket can be sent immediately
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| 54 | (without waiting for the next application write) by calling
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| 55 | SSL_do_handshake(). SSL_new_session_ticket() can be called more than once to
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| 56 | request additional tickets be sent; all such requests are queued and written
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| 57 | together when it is safe to do so and triggered by SSL_write() or
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| 58 | SSL_do_handshake(). Note that a successful return from
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| 59 | SSL_new_session_ticket() indicates only that the request to send a ticket was
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| 60 | processed, not that the ticket itself was sent. To be notified when the
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| 61 | ticket itself is sent, a new-session callback can be registered with
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| 62 | L<SSL_CTX_sess_set_new_cb(3)> that will be invoked as the ticket or tickets
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| 63 | are generated.
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| 64 |
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| 65 | SSL_CTX_get_num_tickets() and SSL_get_num_tickets() return the number of
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| 66 | tickets set by a previous call to SSL_CTX_set_num_tickets() or
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| 67 | SSL_set_num_tickets(), or 2 if no such call has been made.
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| 68 |
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| 69 | =head1 RETURN VALUES
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| 70 |
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| 71 | SSL_CTX_set_num_tickets(), SSL_set_num_tickets(), and
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| 72 | SSL_new_session_ticket() return 1 on success or 0 on failure.
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| 73 |
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| 74 | SSL_CTX_get_num_tickets() and SSL_get_num_tickets() return the number of tickets
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| 75 | that have been previously set.
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| 76 |
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| 77 | =head1 SEE ALSO
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| 78 |
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| 79 | L<ssl(7)>
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| 80 |
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| 81 | =head1 HISTORY
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| 82 |
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| 83 | SSL_new_session_ticket() was added in OpenSSL 3.0.0.
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| 84 | SSL_set_num_tickets(), SSL_get_num_tickets(), SSL_CTX_set_num_tickets(), and
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| 85 | SSL_CTX_get_num_tickets() were added in OpenSSL 1.1.1.
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| 86 |
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| 87 | =head1 COPYRIGHT
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| 88 |
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| 89 | Copyright 2018-2021 The OpenSSL Project Authors. All Rights Reserved.
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| 90 |
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| 91 | Licensed under the Apache License 2.0 (the "License"). You may not use
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| 92 | this file except in compliance with the License. You can obtain a copy
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| 93 | in the file LICENSE in the source distribution or at
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| 94 | L<https://www.openssl.org/source/license.html>.
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| 95 |
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| 96 | =cut
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