OCSP

ocsp − Online Certificate Status Protocol utility

openssl ocsp [−out file] [−issuer file] [−cert file] [−serial n] [−signer file] [−signkey file] [−sign_other file] [−no_certs] [−req_text] [−resp_text] [−text] [−reqout file] [−respout file] [−reqin file] [−respin file] [−nonce] [−no_nonce] [−url URL ] [−host host:n] [−path] [−CApath dir] [−CAfile file] [−VAfile file] [−validity_period n] [−status_age n] [−noverify] [−verify_other file] [−trust_other] [−no_intern] [−no_signature_verify] [−no_cert_verify] [−no_chain] [−no_cert_checks] [−port num] [−index file] [−CA file] [−rsigner file] [−rkey file] [−rother file] [−resp_no_certs] [−nmin n] [−ndays n] [−resp_key_id] [−nrequest n] [−md5|−sha1|...]

The Online Certificate Status Protocol ( OCSP ) enables applications to determine the (revocation) state of an identified certificate ( RFC 2560).

The ocsp command performs many common OCSP tasks. It can be used to print out requests and responses, create requests and send queries to an OCSP responder and behave like a mini OCSP server itself.

−out filename

specify output filename, default is standard output.

−issuer filename

This specifies the current issuer certificate. This option can be used multiple times. The certificate specified in filename must be in PEM format. This option MUST come before any −cert options.

−cert filename

Add the certificate filename to the request. The issuer certificate is taken from the previous issuer option, or an error occurs if no issuer certificate is specified.

−serial num

Same as the cert option except the certificate with serial number num is added to the request. The serial number is interpreted as a decimal integer unless preceded by 0x. Negative integers can also be specified by preceding the value by a − sign.

−signer filename, −signkey filename

Sign the OCSP request using the certificate specified in the signer option and the private key specified by the signkey option. If the signkey option is not present then the private key is read from the same file as the certificate. If neither option is specified then the OCSP request is not signed.

−sign_other filename

Additional certificates to include in the signed request.

−nonce, −no_nonce

Add an OCSP nonce extension to a request or disable OCSP nonce addition. Normally if an OCSP request is input using the respin option no nonce is added: using the nonce option will force addition of a nonce. If an OCSP request is being created (using cert and serial options) a nonce is automatically added specifying no_nonce overrides this.

−req_text, −resp_text, −text

print out the text form of the OCSP request, response or both respectively.

−reqout file, −respout file

write out the DER encoded certificate request or response to file.

−reqin file, −respin file

read OCSP request or response file from file. These option are ignored if OCSP request or response creation is implied by other options (for example with serial, cert and host options).

−url responder_url

specify the responder URL . Both HTTP and HTTPS ( SSL/TLS ) URLs can be specified.

−host hostname:port, −path pathname

if the host option is present then the OCSP request is sent to the host hostname on port port. path specifies the HTTP path name to use or "/" by default.

−CAfile file, −CApath pathname

file or pathname containing trusted CA certificates. These are used to verify the signature on the OCSP response.

−verify_other file

file containing additional certificates to search when attempting to locate the OCSP response signing certificate. Some responders omit the actual signer’s certificate from the response: this option can be used to supply the necessary certificate in such cases.

−trust_other

the certificates specified by the −verify_other option should be explicitly trusted and no additional checks will be performed on them. This is useful when the complete responder certificate chain is not available or trusting a root CA is not appropriate.

−VAfile file

file containing explicitly trusted responder certificates. Equivalent to the −verify_other and −trust_other options.

−noverify

don’t attempt to verify the OCSP response signature or the nonce values. This option will normally only be used for debugging since it disables all verification of the responders certificate.

−no_intern

ignore certificates contained in the OCSP response when searching for the signers certificate. With this option the signers certificate must be specified with either the −verify_other or −VAfile options.

−no_signature_verify

don’t check the signature on the OCSP response. Since this option tolerates invalid signatures on OCSP responses it will normally only be used for testing purposes.

−no_cert_verify

don’t verify the OCSP response signers certificate at all. Since this option allows the OCSP response to be signed by any certificate it should only be used for testing purposes.

−no_chain

do not use certificates in the response as additional untrusted CA certificates.

−no_cert_checks

don’t perform any additional checks on the OCSP response signers certificate. That is do not make any checks to see if the signers certificate is authorised to provide the necessary status information: as a result this option should only be used for testing purposes.

−validity_period nsec, −status_age age

these options specify the range of times, in seconds, which will be tolerated in an OCSP response. Each certificate status response includes a notBefore time and an optional notAfter time. The current time should fall between these two values, but the interval between the two times may be only a few seconds. In practice the OCSP responder and clients clocks may not be precisely synchronised and so such a check may fail. To avoid this the −validity_period option can be used to specify an acceptable error range in seconds, the default value is 5 minutes.

If the notAfter time is omitted from a response then this means that new status information is immediately available. In this case the age of the notBefore field is checked to see it is not older than age seconds old. By default this additional check is not performed.

−md5|−sha1|−sha256|−ripemod160|...

this option sets digest algorithm to use for certificate identification in the OCSP request. By default SHA−1 is used.

−index indexfile

indexfile is a text index file in ca format containing certificate revocation information.

If the index option is specified the ocsp utility is in responder mode, otherwise it is in client mode. The request(s) the responder processes can be either specified on the command line (using issuer and serial options), supplied in a file (using the respin option) or via external OCSP clients (if port or url is specified).

If the index option is present then the CA and rsigner options must also be present.

−CA file

CA certificate corresponding to the revocation information in indexfile.

−rsigner file

The certificate to sign OCSP responses with.

−rother file

Additional certificates to include in the OCSP response.

−resp_no_certs

Don’t include any certificates in the OCSP response.

−resp_key_id

Identify the signer certificate using the key ID , default is to use the subject name.

−rkey file

The private key to sign OCSP responses with: if not present the file specified in the rsigner option is used.

−port portnum

Port to listen for OCSP requests on. The port may also be specified using the url option.

−nrequest number

The OCSP server will exit after receiving number requests, default unlimited.

−nmin minutes, −ndays days

Number of minutes or days when fresh revocation information is available: used in the nextUpdate field. If neither option is present then the nextUpdate field is omitted meaning fresh revocation information is immediately available.

OCSP Response follows the rules specified in RFC2560 .

Initially the OCSP responder certificate is located and the signature on the OCSP request checked using the responder certificate’s public key.

Then a normal certificate verify is performed on the OCSP responder certificate building up a certificate chain in the process. The locations of the trusted certificates used to build the chain can be specified by the CAfile and CApath options or they will be looked for in the standard OpenSSL certificates directory.

If the initial verify fails then the OCSP verify process halts with an error.

Otherwise the issuing CA certificate in the request is compared to the OCSP responder certificate: if there is a match then the OCSP verify succeeds.

Otherwise the OCSP responder certificate’s CA is checked against the issuing CA certificate in the request. If there is a match and the OCSPSigning extended key usage is present in the OCSP responder certificate then the OCSP verify succeeds.

Otherwise the root CA of the OCSP responders CA is checked to see if it is trusted for OCSP signing. If it is the OCSP verify succeeds.

If none of these checks is successful then the OCSP verify fails.

What this effectively means if that if the OCSP responder certificate is authorised directly by the CA it is issuing revocation information about (and it is correctly configured) then verification will succeed.

If the OCSP responder is a "global responder" which can give details about multiple CAs and has its own separate certificate chain then its root CA can be trusted for OCSP signing. For example:

 openssl x509 −in ocspCA.pem −addtrust OCSPSigning −out trustedCA.pem

Alternatively the responder certificate itself can be explicitly trusted with the −VAfile option.

As noted, most of the verify options are for testing or debugging purposes. Normally only the −CApath, −CAfile and (if the responder is a ’global VA ’) −VAfile options need to be used.

The OCSP server is only useful for test and demonstration purposes: it is not really usable as a full OCSP responder. It contains only a very simple HTTP request handling and can only handle the POST form of OCSP queries. It also handles requests serially meaning it cannot respond to new requests until it has processed the current one. The text index file format of revocation is also inefficient for large quantities of revocation data.

It is possible to run the ocsp application in responder mode via a CGI script using the respin and respout options.

Create an OCSP request and write it to a file:

 openssl ocsp −issuer issuer.pem −cert c1.pem −cert c2.pem −reqout req.der

Send a query to an OCSP responder with URL http://ocsp.myhost.com/ save the response to a file and print it out in text form

 openssl ocsp −issuer issuer.pem −cert c1.pem −cert c2.pem \
     −url http://ocsp.myhost.com/ −resp_text −respout resp.der

Read in an OCSP response and print out text form:

 openssl ocsp −respin resp.der −text

OCSP server on port 8888 using a standard ca configuration, and a separate responder certificate. All requests and responses are printed to a file.

 openssl ocsp −index demoCA/index.txt −port 8888 −rsigner rcert.pem −CA demoCA/cacert.pem
        −text −out log.txt

As above but exit after processing one request:

 openssl ocsp −index demoCA/index.txt −port 8888 −rsigner rcert.pem −CA demoCA/cacert.pem
     −nrequest 1

Query status information using internally generated request:

 openssl ocsp −index demoCA/index.txt −rsigner rcert.pem −CA demoCA/cacert.pem
     −issuer demoCA/cacert.pem −serial 1

Query status information using request read from a file, write response to a second file.

 openssl ocsp −index demoCA/index.txt −rsigner rcert.pem −CA demoCA/cacert.pem
     −reqin req.der −respout resp.der