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() copys 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 non-zero 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 2015-2016 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 <https://www.openssl.org/source/license.html>.