ocsptool - GnuTLS OCSP tool

NAME SYNOPSIS DESCRIPTION OPTIONS EXAMPLES EXIT STATUS SEE ALSO AUTHORS COPYRIGHT BUGS

SYNOPSIS

ocsptool [−flags] [−flag [value]] [−−option-name[[=| ]value]]

All arguments must be options.

On verification
Responses are typically signed/issued by designated certificates or certificate authorities and thus this tool requires on verification the certificate of the issuer or the full certificate chain in order to determine the appropriate signing authority. The specified certificate of the issuer is assumed trusted.

OPTIONS

−d num, −−debug=num Enable debugging. This option takes an integer
number as its argument. The value of num is constrained to being:

in the range 0 through 9999

Specifies the debug level.

−V, −−verbose More verbose output.

−−infile=file Input file.

−−outfile=str Output file.

−−ask=server name|url Ask an OCSP/HTTP server on a certificate
validity.

Connects to the specified HTTP OCSP server and queries on the validity
of the loaded certificate. Its argument can be a URL or a plain server
name. It can be combined with −−load−chain, where it checks all
certificates in the provided chain, or with −−load−cert and
−−load−issuer options. The latter checks the provided certificate
against its specified issuer certificate.

−e, −−verify−response Verify response.

Verifies the provided OCSP response against the system trust anchors
(unless −−load−trust is provided). It requires the −−load−signer or
−−load−chain options to obtain the signer of the OCSP response.

−i, −−request−info Print information on a OCSP request.

Display detailed information on the provided OCSP request.

−j, −−response−info Print information on a OCSP response.

Display detailed information on the provided OCSP response.

−q, −−generate−request Generates an OCSP request.

−−nonce, −−no−nonce Use (or not) a nonce to OCSP request. The no−nonce
form will disable the option.

−−load−chain=file Reads a set of certificates forming a chain from
file.

−−load−issuer=file Reads issuer’s certificate from file.

−−load−cert=file Reads the certificate to check from file.

−−load−trust=file Read OCSP trust anchors from file. This option must
not appear in combination with any of the following options:
load-signer.

When verifying an OCSP response read the trust anchors from the
provided file. When this is not provided, the system’s trust anchors
will be used.

−−load−signer=file Reads the OCSP response signer from file. This
option must not appear in combination with any of the following
options: load-trust.

−−inder, −−no−inder Use DER format for input certificates and private
keys. The no−inder form will disable the option.

−−outder Use DER format for output of responses (this is the default).

The output will be in DER encoded format. Unlike other GnuTLS tools,
this is the default for this tool

−−outpem Use PEM format for output of responses.

The output will be in PEM format.

−Q file, −−load−request=file Reads the DER encoded OCSP request from
file.

−S file, −−load−response=file Reads the DER encoded OCSP response from
file.

−−ignore−errors Ignore any verification errors.

−−verify−allow−broken Allow broken algorithms, such as MD5 for
verification.

This can be combined with −−verify−response.

−−attime=timestamp Perform validation at the timestamp instead of the
system time.

timestamp is an instance in time encoded as Unix time or in a human
readable timestring such as "29 Feb 2004", "2004−02−29". Full
documentation available at
<https://www.gnu.org/software/coreutils/manual/html_node/Date−input−formats.html>
or locally via info ’(coreutils) date invocation’.

−v arg, −−version=arg 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.

−h, −−help Display usage information and exit.

−!, −−more−help Pass the extended usage information through a pager.

EXAMPLES

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 −−save−cert chain.pem

The saved certificates normally contain a pointer to where the OCSP responder is located, in the Authority Information Access Information extension. For example, from certtool −i < chain.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: https://ocsp.CAcert.org/

This means that ocsptool can discover the servers to contact over HTTP. We can now request information on the chain certificates.

$ ocsptool −−ask −−load−chain chain.pem

The request is sent via HTTP to the OCSP server address found in the certificates. It is possible to override the address of the OCSP server as well as ask information on a particular certificate using −−load−cert and −−load−issuer.

$ ocsptool −−ask https://ocsp.CAcert.org/ −−load−chain chain.pem