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=pod
=head1 NAME
OCSP_request_add1_nonce, OCSP_basic_add1_nonce, OCSP_check_nonce, OCSP_copy_nonce - OCSP nonce functions
=head1 SYNOPSIS
#include <openssl/ocsp.h>
int OCSP_request_add1_nonce(OCSP_REQUEST *req, unsigned char *val, int len);
int OCSP_basic_add1_nonce(OCSP_BASICRESP *resp, unsigned char *val, int len);
int OCSP_copy_nonce(OCSP_BASICRESP *resp, OCSP_REQUEST *req);
int OCSP_check_nonce(OCSP_REQUEST *req, OCSP_BASICRESP *resp);
=head1 DESCRIPTION
OCSP_request_add1_nonce() adds a nonce of value B<val> and length B<len> to
OCSP request B<req>. If B<val> is B<NULL> a random nonce is used. If B<len>
is zero or negative a default length will be used (currently 16 bytes).
OCSP_basic_add1_nonce() is identical to OCSP_request_add1_nonce() except
it adds a nonce to OCSP basic response B<resp>.
OCSP_check_nonce() compares the nonce value in B<req> and B<resp>.
OCSP_copy_nonce() copies any nonce value present in B<req> to B<resp>.
=head1 RETURN VALUES
OCSP_request_add1_nonce() and OCSP_basic_add1_nonce() return 1 for success
and 0 for failure.
OCSP_copy_nonce() returns 1 if a nonce was successfully copied, 2 if no nonce
was present in B<req> and 0 if an error occurred.
OCSP_check_nonce() returns the result of the nonce comparison between B<req>
and B<resp>. The return value indicates the result of the comparison. If
nonces are present and equal 1 is returned. If the nonces are absent 2 is
returned. If a nonce is present in the response only 3 is returned. If nonces
are present and unequal 0 is returned. If the nonce is present in the request
only then -1 is returned.
=head1 NOTES
For most purposes the nonce value in a request is set to a random value so
the B<val> parameter in OCSP_request_add1_nonce() is usually NULL.
An OCSP nonce is typically added to an OCSP request to thwart replay attacks
by checking the same nonce value appears in the response.
Some responders may include a nonce in all responses even if one is not
supplied.
Some responders cache OCSP responses and do not sign each response for
performance reasons. As a result they do not support nonces.
The return values of OCSP_check_nonce() can be checked to cover each case. A
positive return value effectively indicates success: nonces are both present
and match, both absent or present in the response only. A nonzero return
additionally covers the case where the nonce is present in the request only:
this will happen if the responder doesn't support nonces. A zero return value
indicates present and mismatched nonces: this should be treated as an error
condition.
=head1 SEE ALSO
L<crypto(7)>,
L<OCSP_cert_to_id(3)>,
L<OCSP_REQUEST_new(3)>,
L<OCSP_resp_find_status(3)>,
L<OCSP_response_status(3)>,
L<OCSP_sendreq_new(3)>
=head1 COPYRIGHT
Copyright 2015-2020 The OpenSSL Project Authors. All Rights Reserved.
Licensed under the OpenSSL license (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
L<https://www.openssl.org/source/license.html>.
=cut
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