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ocsptool — GnuTLS OCSP tool
ocsptool [ −flag [value] ...] [ −−opt−name [[=|]value] ...]
Ocsptool is a program that can parse and print information about OCSP requests/responses, generate requests and verify responses.
−d
number,
−−debug=numberEnable debugging. This option takes an integer number as its argument. The value of number is constrained to being:
in the range 0 through 9999
Specifies the debug level.
−V,
−−verboseMore verbose output. This option may appear an unlimited number of times.
−−infile=fileInput file.
−−outfile=stringOutput file.
−−ask[=server
name|url]Ask an OCSP/HTTP server on a certificate validity. This option must appear in combination with the following options: load-cert, load-issuer.
Connects to the specified HTTP OCSP server and queries on the validity of the loaded certificate.
−e,
−−verify−responseVerify response.
−i,
−−request−infoPrint information on a OCSP request.
−j,
−−response−infoPrint information on a OCSP response.
−q,
−−generate−requestGenerate an OCSP request.
−−nonce, −−no−nonceDon't add nonce to OCSP request. The no−nonce form
will disable the option.
−−load−issuer=fileRead issuer certificate from file.
−−load−cert=fileRead certificate to check from file.
−−load−trust=fileRead OCSP trust anchors from file. This option must not appear in combination with any of the following options: load-signer.
−−load−signer=fileRead OCSP response signer from file. This option must not appear in combination with any of the following options: load-trust.
−−inder, −−no−inderUse DER format for input certificates and private
keys. The no−inder form
will disable the option.
−Q
file,
−−load−request=fileRead DER encoded OCSP request from file.
−S
file,
−−load−response=fileRead DER encoded OCSP response from file.
−h,
−−helpDisplay usage information and exit.
−!,
−−more−helpPass the extended usage information through a pager.
−v
[{v|c|n}],
−−version[={v|c|n}]Output version of program and exit. The default mode is `v', a simple version. The `c' mode will print copyright information and `n' will print the full copyright notice.
Print information about an OCSP request
To parse an OCSP request and print information about the
content, the −i or
−−request−info
parameter may be used as follows. The −Q parameter specify the name of the
file containing the OCSP request, and it should contain the
OCSP request in binary DER format.
$ ocsptool −i −Q ocsp−request.der
The input file may also be sent to standard input like this:
$ cat ocsp−request.der | ocsptool −−request−info
Print information about an OCSP response
Similar to parsing OCSP requests, OCSP responses can be
parsed using the −j or
−−response−info
as follows.
$ ocsptool −j −Q ocsp−response.der $ cat ocsp−response.der | ocsptool −−response−info
Generate an OCSP request
The −q or −−generate−request
parameters are used to generate an OCSP request. By default
the OCSP request is written to standard output in binary DER
format, but can be stored in a file using −−outfile. To generate an OCSP
request the issuer of the certificate to check needs to be
specified with −−load−issuer and the
certificate to check with −−load−cert. By default PEM
format is used for these files, although −−inder can be used to specify
that the input files are in DER format.
$ ocsptool −q −−load−issuer issuer.pem −−load−cert client.pem −−outfile ocsp−request.der
When generating OCSP requests, the tool will add an OCSP
extension containing a nonce. This behaviour can be disabled
by specifying −−no−nonce.
Verify signature in OCSP response
To verify the signature in an OCSP response the
−e or −−verify−response parameter
is used. The tool will read an OCSP response in DER format
from standard input, or from the file specified by
−−load−response. The OCSP
response is verified against a set of trust anchors, which
are specified using −−load−trust. The trust
anchors are concatenated certificates in PEM format. The
certificate that signed the OCSP response needs to be in the
set of trust anchors, or the issuer of the signer certificate
needs to be in the set of trust anchors and the OCSP Extended
Key Usage bit has to be asserted in the signer
certificate.
$ ocsptool −e −−load−trust issuer.pem −−load−response ocsp−response.der
The tool will print status of verification.
Verify signature in OCSP response against given certificate
It is possible to override the normal trust logic if you
know that a certain certificate is supposed to have signed
the OCSP response, and you want to use it to check the
signature. This is achieved using −−load−signer instead of
−−load−trust.
This will load one certificate and it will be used to verify
the signature in the OCSP response. It will not check the
Extended Key Usage bit.
$ ocsptool −e −−load−signer ocsp−signer.pem −−load−response ocsp−response.der
This approach is normally only relevant in two situations.
The first is when the OCSP response does not contain a copy
of the signer certificate, so the −−load−trust code would
fail. The second is if you want to avoid the indirect mode
where the OCSP response signer certificate is signed by a
trust anchor.
Real−world example
Here is an example of how to generate an OCSP request for
a certificate and to verify the response. For illustration
we'll use the blog.josefsson.org host,
which (as of writing) uses a certificate from CACert. First
we'll use gnutls−cli to get a
copy of the server certificate chain. The server is not
required to send this information, but this particular one is
configured to do so.
$ echo | gnutls−cli −p 443 blog.josefsson.org −−print−cert > chain.pem
Use a text editor on chain.pem to create three
files for each separate certificates, called cert.pem for the first
certificate for the domain itself, secondly issuer.pem for the
intermediate certificate and root.pem for the final root
certificate.
The domain certificate normally contains a pointer to where the OCSP responder is located, in the Authority Information Access Information extension. For example, from certtool −i < cert.pem there is this information:
Authority Information Access Information (not critical): Access Method: 1.3.6.1.5.5.7.48.1 (id−ad−ocsp) Access Location URI: http://ocsp.CAcert.org/
This means the CA support OCSP queries over HTTP. We are now ready to create a OCSP request for the certificate.
$ ocsptool −−ask ocsp.CAcert.org −−load−issuer issuer.pem −−load−cert cert.pem −−outfile ocsp−response.der
The request is sent via HTTP to the OCSP server address specified. If the address is ommited ocsptool will use the address stored in the certificate.
One of the following exit values will be returned:
0 (EXIT_SUCCESS)
Successful program execution.
1 (EXIT_FAILURE)
The operation failed or the command syntax was not valid.
70 (EX_SOFTWARE)
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