NAME

       OCSP_request_add1_nonce, OCSP_basic_add1_nonce, OCSP_check_nonce, OCSP_copy_nonce - OCSP
       nonce functions

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);

DESCRIPTION

       OCSP_request_add1_nonce() adds a nonce of value val and length len to OCSP request req. If
       val is NULL a random nonce is used. If 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 resp.

       OCSP_check_nonce() compares the nonce value in req and resp.

       OCSP_copy_nonce() copies any nonce value present in req to resp.

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 req and 0 if an error occurred.

       OCSP_check_nonce() returns the result of the nonce comparison between req and 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.

NOTES

       For most purposes the nonce value in a request is set to a random value so the 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.

SEE ALSO

       crypto(7), OCSP_cert_to_id(3), OCSP_REQUEST_new(3), OCSP_resp_find_status(3),
       OCSP_response_status(3), OCSP_sendreq_new(3)

COPYRIGHT

       Copyright 2015-2020 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>.