158 lines
6.3 KiB
Plaintext
158 lines
6.3 KiB
Plaintext
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=pod
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=head1 NAME
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SSL_psk_server_cb_func,
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SSL_psk_find_session_cb_func,
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SSL_CTX_use_psk_identity_hint,
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SSL_use_psk_identity_hint,
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SSL_CTX_set_psk_server_callback,
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SSL_set_psk_server_callback,
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SSL_CTX_set_psk_find_session_callback,
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SSL_set_psk_find_session_callback
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- set PSK identity hint to use
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=head1 SYNOPSIS
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#include <openssl/ssl.h>
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typedef int (*SSL_psk_find_session_cb_func)(SSL *ssl,
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const unsigned char *identity,
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size_t identity_len,
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SSL_SESSION **sess);
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void SSL_CTX_set_psk_find_session_callback(SSL_CTX *ctx,
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SSL_psk_find_session_cb_func cb);
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void SSL_set_psk_find_session_callback(SSL *s, SSL_psk_find_session_cb_func cb);
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typedef unsigned int (*SSL_psk_server_cb_func)(SSL *ssl,
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const char *identity,
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unsigned char *psk,
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unsigned int max_psk_len);
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int SSL_CTX_use_psk_identity_hint(SSL_CTX *ctx, const char *hint);
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int SSL_use_psk_identity_hint(SSL *ssl, const char *hint);
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void SSL_CTX_set_psk_server_callback(SSL_CTX *ctx, SSL_psk_server_cb_func cb);
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void SSL_set_psk_server_callback(SSL *ssl, SSL_psk_server_cb_func cb);
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=head1 DESCRIPTION
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A server application wishing to use TLSv1.3 PSKs should set a callback
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using either SSL_CTX_set_psk_find_session_callback() or
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SSL_set_psk_find_session_callback() as appropriate.
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The callback function is given a pointer to the SSL connection in B<ssl> and
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an identity in B<identity> of length B<identity_len>. The callback function
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should identify an SSL_SESSION object that provides the PSK details and store it
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in B<*sess>. The SSL_SESSION object should, as a minimum, set the master key,
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the ciphersuite and the protocol version. See
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L<SSL_CTX_set_psk_use_session_callback(3)> for details.
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It is also possible for the callback to succeed but not supply a PSK. In this
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case no PSK will be used but the handshake will continue. To do this the
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callback should return successfully and ensure that B<*sess> is
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NULL.
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Identity hints are not relevant for TLSv1.3. A server application wishing to use
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PSK ciphersuites for TLSv1.2 and below may call SSL_CTX_use_psk_identity_hint()
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to set the given B<NUL>-terminated PSK identity hint B<hint> for SSL context
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object B<ctx>. SSL_use_psk_identity_hint() sets the given B<NUL>-terminated PSK
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identity hint B<hint> for the SSL connection object B<ssl>. If B<hint> is
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B<NULL> the current hint from B<ctx> or B<ssl> is deleted.
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In the case where PSK identity hint is B<NULL>, the server does not send the
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ServerKeyExchange message to the client.
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A server application wishing to use PSKs for TLSv1.2 and below must provide a
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callback function which is called when the server receives the
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ClientKeyExchange message from the client. The purpose of the callback function
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is to validate the received PSK identity and to fetch the pre-shared key used
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during the connection setup phase. The callback is set using the functions
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SSL_CTX_set_psk_server_callback() or SSL_set_psk_server_callback(). The callback
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function is given the connection in parameter B<ssl>, B<NUL>-terminated PSK
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identity sent by the client in parameter B<identity>, and a buffer B<psk> of
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length B<max_psk_len> bytes where the pre-shared key is to be stored.
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The callback for use in TLSv1.2 will also work in TLSv1.3 although it is
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recommended to use SSL_CTX_set_psk_find_session_callback()
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or SSL_set_psk_find_session_callback() for this purpose instead. If TLSv1.3 has
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been negotiated then OpenSSL will first check to see if a callback has been set
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via SSL_CTX_set_psk_find_session_callback() or SSL_set_psk_find_session_callback()
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and it will use that in preference. If no such callback is present then it will
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check to see if a callback has been set via SSL_CTX_set_psk_server_callback() or
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SSL_set_psk_server_callback() and use that. In this case the handshake digest
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will default to SHA-256 for any returned PSK. TLSv1.3 early data exchanges are
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possible in PSK connections only with the B<SSL_psk_find_session_cb_func>
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callback, and are not possible with the B<SSL_psk_server_cb_func> callback.
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=head1 NOTES
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A connection established via a TLSv1.3 PSK will appear as if session resumption
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has occurred so that L<SSL_session_reused(3)> will return true.
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=head1 RETURN VALUES
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B<SSL_CTX_use_psk_identity_hint()> and B<SSL_use_psk_identity_hint()> return
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1 on success, 0 otherwise.
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Return values from the TLSv1.2 and below server callback are interpreted as
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follows:
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=over 4
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=item Z<>0
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PSK identity was not found. An "unknown_psk_identity" alert message
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will be sent and the connection setup fails.
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=item E<gt>0
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PSK identity was found and the server callback has provided the PSK
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successfully in parameter B<psk>. Return value is the length of
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B<psk> in bytes. It is an error to return a value greater than
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B<max_psk_len>.
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If the PSK identity was not found but the callback instructs the
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protocol to continue anyway, the callback must provide some random
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data to B<psk> and return the length of the random data, so the
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connection will fail with decryption_error before it will be finished
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completely.
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=back
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The B<SSL_psk_find_session_cb_func> callback should return 1 on success or 0 on
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failure. In the event of failure the connection setup fails.
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=head1 NOTES
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There are no known security issues with sharing the same PSK between TLSv1.2 (or
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below) and TLSv1.3. However, the RFC has this note of caution:
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"While there is no known way in which the same PSK might produce related output
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in both versions, only limited analysis has been done. Implementations can
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ensure safety from cross-protocol related output by not reusing PSKs between
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TLS 1.3 and TLS 1.2."
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=head1 SEE ALSO
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L<SSL_CTX_set_psk_use_session_callback(3)>,
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L<SSL_set_psk_use_session_callback(3)>
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=head1 HISTORY
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SSL_CTX_set_psk_find_session_callback() and SSL_set_psk_find_session_callback()
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were added in OpenSSL 1.1.1.
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=head1 COPYRIGHT
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Copyright 2006-2020 The OpenSSL Project Authors. All Rights Reserved.
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Licensed under the OpenSSL license (the "License"). You may not use
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this file except in compliance with the License. You can obtain a copy
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in the file LICENSE in the source distribution or at
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L<https://www.openssl.org/source/license.html>.
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=cut
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