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.
OCSP CLIENT OPTIONS
-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.
-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_certs 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_certs 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_certs 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.
OCSP SERVER OPTIONS
-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 verification.
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:
Alternatively the responder certificate itself can be explicitly trusted
with the -VAfile option.
NOTES
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.
