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OCSP response unauthorized or unsuccessful

Windows OCSP client requires that the OCSP responder URL is populated in the AIA extension. If it is not included, Windows will not form the OCSP request properly and the validation will fail with Certutil status of "Unsuccessful". The same certificate was successfully validated by a Cisco ASA OCSP client. 

 According to the RFC2560 Apendix A.1.1:

 
{url} may be derived from the value of AuthorityInfoAccess or
   other local configuration of the OCSP client.

 This does not seem to be the case in Microsoft's implementation. 

OCSP responder address is specified in the Authority Information Access (AIA) extension. In Windows CA, this is configured in the properties of the CA on the"Extensions" tab.


 Once configured all newly issued certificates will include the OCSP responder address.

Without the OCSP extension validation using certutil fails.


According to RFC2560, an OCSP request must specify hashing algorithm, issuer name hash, issuer key hash and serial number of the certificate to be validated. 

 Extract from RFC2560:

CertID          ::=     SEQUENCE {
  hashAlgorithm       AlgorithmIdentifier,
  issuerNameHash      OCTET STRING, -- Hash of Issuer's DN
  issuerKeyHash       OCTET STRING, -- Hash of Issuers public key


  serialNumber        CertificateSerialNumber }

issuerNameHash is the hash of the Issuer's distinguished name. The hash shall be calculated over the DER encoding of the issuer's name field in the certificate being checked. IsuerKeyHash is the hash of the Issuer's public key. The hash shall be calculated over the value(excluding tag and length) of the subject public key field in the issuer's certificate. The hash algorithm used for both these hashes, is identified in hashAlgorithm. serialNumber is the serial number of the certificate for which status is being requested.








If the AIA extension doesn't specify the OCSP URL Windows client does not include issuer's key hash in the request. 


In this case the responder returns an error of "unauthorized" and the validation fails. 


 Extract from RFC2560:

2.3 Exception Cases

In case of errors, the OCSP Responder may return an error message. These messages are not signed. Errors can be of the following types:

   -- malformedRequest
   -- internalError
   -- tryLater
   -- sigRequired
   -- unauthorized

The response "unauthorized" is returned in cases where the client is not authorized to make this query to this server.
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