4.2.7 Invoking ocsptool

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.

ocsptool help/usage (-?)

The text printed is the same whether selected with the help option (--help) or the more-help option (--more-help). more-help will print the usage text by passing it through a pager program. more-help is disabled on platforms without a working fork(2) function. The PAGER environment variable is used to select the program, defaulting to more. Both will exit with a status code of 0.

ocsptool - GnuTLS OCSP tool
Usage:  ocsptool [ -<flag> [<val>] | --<name>[{=| }<val>] ]... 

None:

   -d, --debug=num            Enable debugging
				- it must be in the range:
				  0 to 9999
   -V, --verbose              More verbose output
       --infile=file          Input file
				- file must pre-exist
       --outfile=str          Output file
       --ask[=str]            Ask an OCSP/HTTP server on a certificate validity
   -e, --verify-response      Verify response
   -i, --request-info         Print information on a OCSP request
   -j, --response-info        Print information on a OCSP response
   -q, --generate-request     Generates an OCSP request
       --nonce                Use (or not) a nonce to OCSP request
       --load-chain=file      Reads a set of certificates forming a chain from file
				- file must pre-exist
       --load-issuer=file     Reads issuer's certificate from file
				- file must pre-exist
       --load-cert=file       Reads the certificate to check from file
				- file must pre-exist
       --load-trust=file      Read OCSP trust anchors from file
				- prohibits the option 'load-signer'
				- file must pre-exist
       --load-signer=file     Reads the OCSP response signer from file
				- prohibits the option 'load-trust'
				- file must pre-exist
       --inder                Use DER format for input certificates and private keys
       --outder               Use DER format for output of responses (this is the default)
       --outpem               Use PEM format for output of responses
   -Q, --load-request=file    Reads the DER encoded OCSP request from file
				- file must pre-exist
   -S, --load-response=file   Reads the DER encoded OCSP response from file
				- file must pre-exist
       --ignore-errors        Ignore any verification errors
       --verify-allow-broken  Allow broken algorithms, such as MD5 for verification
       --attime=str           Perform validation at the timestamp instead of the system time

Version, usage and configuration options:

   -v, --version[=arg]        output version information and exit
   -h, --help                 display extended usage information and exit
   -!, --more-help            extended usage information passed thru pager

Options are specified by doubled hyphens and their name or by a single
hyphen and the flag character.

ocsptool is a program that can parse and print information about
OCSP requests/responses, generate requests and verify responses. Unlike
other GnuTLS applications it outputs DER encoded structures by default
unless the '--outpem' option is specified.

Please send bug reports to:  <bugs@gnutls.org>

debug option (-d).

This is the “enable debugging” option. This option takes a ArgumentType.NUMBER argument. Specifies the debug level.

ask option.

This is the “ask an ocsp/http server on a certificate validity” option. This option takes a ArgumentType.STRING argument server name|url. 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.

verify-response option (-e).

This is the “verify response” option. 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.

request-info option (-i).

This is the “print information on a ocsp request” option. Display detailed information on the provided OCSP request.

response-info option (-j).

This is the “print information on a ocsp response” option. Display detailed information on the provided OCSP response.

load-trust option.

This is the “read ocsp trust anchors from file” option. This option takes a ArgumentType.FILE argument.

This option has some usage constraints. It:

• 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.

outder option.

This is the “use der format for output of responses (this is the default)” option. The output will be in DER encoded format. Unlike other GnuTLS tools, this is the default for this tool

outpem option.

This is the “use pem format for output of responses” option. The output will be in PEM format.

verify-allow-broken option.

This is the “allow broken algorithms, such as md5 for verification” option. This can be combined with –verify-response.

attime option.

This is the “perform validation at the timestamp instead of the system time” option. This option takes a ArgumentType.STRING argument timestamp. 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’.

version option (-v).

This is the “output version information and exit” option. This option takes a ArgumentType.KEYWORD argument. 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.

help option (-h).

This is the “display extended usage information and exit” option. Display usage information and exit.

more-help option (-!).

This is the “extended usage information passed thru pager” option. Pass the extended usage information through a pager.

ocsptool exit status

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.

ocsptool See Also

certtool (1)

ocsptool 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