| 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_session_secret_cb, tls_session_secret_cb_fn
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| 6 | - set the session secret callback
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| 7 |
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| 8 | =head1 SYNOPSIS
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| 9 |
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| 10 | #include <openssl/ssl.h>
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| 11 |
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| 12 | typedef int (*tls_session_secret_cb_fn)(SSL *s, void *secret, int *secret_len,
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| 13 | STACK_OF(SSL_CIPHER) *peer_ciphers,
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| 14 | const SSL_CIPHER **cipher, void *arg);
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| 15 |
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| 16 | int SSL_set_session_secret_cb(SSL *s,
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| 17 | tls_session_secret_cb_fn session_secret_cb,
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| 18 | void *arg);
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| 19 |
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| 20 | =head1 DESCRIPTION
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| 21 |
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| 22 | SSL_set_session_secret_cb() sets the session secret callback to be used
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| 23 | (I<session_secret_cb>), and an optional argument (I<arg>) to be passed to that
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| 24 | callback when it is called. This is only useful for an implementation of
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| 25 | EAP-FAST (RFC4851). The presence of the callback also modifies the internal
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| 26 | OpenSSL TLS state machine to match the modified TLS behaviour as described in
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| 27 | RFC4851. Therefore this callback should not be used except when implementing
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| 28 | EAP-FAST.
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| 29 |
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| 30 | The callback is expected to set the master secret to be used by filling in the
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| 31 | data pointed to by I<*secret>. The size of the secret buffer is initially
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| 32 | available in I<*secret_len> and may be updated by the callback (but must not be
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| 33 | larger than the initial value).
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| 34 |
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| 35 | On the server side the set of ciphersuites offered by the peer is provided in
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| 36 | the I<peer_ciphers> stack. Optionally the callback may select the preferred
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| 37 | ciphersuite by setting it in I<*cipher>.
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| 38 |
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| 39 | On the client side the I<peer_ciphers> stack will always be NULL. The callback
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| 40 | may specify the preferred cipher in I<*cipher> and this will be associated with
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| 41 | the B<SSL_SESSION> - but it does not affect the ciphersuite selected by the
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| 42 | server.
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| 43 |
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| 44 | The callback is also supplied with an additional argument in I<arg> which is the
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| 45 | argument that was provided to the original SSL_set_session_secret_cb() call.
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| 46 |
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| 47 | =head1 RETURN VALUES
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| 48 |
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| 49 | SSL_set_session_secret_cb() returns 1 on success and 0 on failure.
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| 50 |
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| 51 | If the callback returns 1 then this indicates it has successfully set the
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| 52 | secret. A return value of 0 indicates that the secret has not been set. On the
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| 53 | client this will cause an immediate abort of the handshake.
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| 54 |
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| 55 | =head1 SEE ALSO
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| 56 |
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| 57 | L<ssl(7)>,
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| 58 | L<SSL_get_session(3)>
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| 59 |
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| 60 | =head1 COPYRIGHT
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| 61 |
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| 62 | Copyright 2024 The OpenSSL Project Authors. All Rights Reserved.
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| 63 |
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| 64 | Licensed under the Apache License 2.0 (the "License"). You may not use
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| 65 | this file except in compliance with the License. You can obtain a copy
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| 66 | in the file LICENSE in the source distribution or at
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| 67 | L<https://www.openssl.org/source/license.html>.
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| 68 |
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| 69 | =cut
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