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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.

This section was generated by *AutoGen*, using the 'agtexi-cmd' template
and the option descriptions for the 'ocsptool' program.  This software
is released under the GNU General Public License, version 3 or later.

ocsptool help/usage ('--help')
..............................

This is the automatically generated usage text for ocsptool.

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>] ]...

        -d, --debug=num            Enable debugging
                                     - it must be in the range:
                                       0 to 9999
        -V, --verbose              More verbose output
                                     - may appear multiple times
            --infile=file          Input file
                                     - file must pre-exist
            --outfile=str          Output file
            --ask[=arg]            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
                                     - disabled as '--no-nonce'
            --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
                                     - disabled as '--no-inder'
            --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
        -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.


debug option (-d)
.................

This is the "enable debugging" option.  This option takes a number
argument.  Specifies the debug level.

ask option
..........

This is the "ask an ocsp/http server on a certificate validity" option.
This option takes an optional 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 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.

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