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2.3 Configuration

There are a few configuration files needed for the operation of the agent. By default they may all be found in the current home directory (see option –homedir).

gpg-agent.conf
This is the standard configuration file read by gpg-agent on startup. It may contain any valid long option; the leading two dashes may not be entered and the option may not be abbreviated. This file is also read after a SIGHUP however only a few options will actually have an effect. This default name may be changed on the command line (see option –options). You should backup this file.
trustlist.txt
This is the list of trusted keys. You should backup this file.

Comment lines, indicated by a leading hash mark, as well as empty lines are ignored. To mark a key as trusted you need to enter its fingerprint followed by a space and a capital letter S. Colons may optionally be used to separate the bytes of a fingerprint; this allows to cut and paste the fingerprint from a key listing output. If the line is prefixed with a ! the key is explicitly marked as not trusted.

Here is an example where two keys are marked as ultimately trusted and one as not trusted:

            # CN=Wurzel ZS 3,O=Intevation GmbH,C=DE
            A6935DD34EF3087973C706FC311AA2CCF733765B S
          
            # CN=PCA-1-Verwaltung-02/O=PKI-1-Verwaltung/C=DE
            DC:BD:69:25:48:BD:BB:7E:31:6E:BB:80:D3:00:80:35:D4:F8:A6:CD S
          
            # CN=Root-CA/O=Schlapphuete/L=Pullach/C=DE
            !14:56:98:D3:FE:9C:CA:5A:31:6E:BC:81:D3:11:4E:00:90:A3:44:C2 S

Before entering a key into this file, you need to ensure its authenticity. How to do this depends on your organisation; your administrator might have already entered those keys which are deemed trustworthy enough into this file. Places where to look for the fingerprint of a root certificate are letters received from the CA or the website of the CA (after making 100% sure that this is indeed the website of that CA). You may want to consider allowing interactive updates of this file by using the See option –allow-mark-trusted. This is however not as secure as maintaining this file manually. It is even advisable to change the permissions to read-only so that this file can't be changed inadvertently.

As a special feature a line include-default will include a global list of trusted certificates (e.g. /etc/gnupg/trustlist.txt). This global list is also used if the local list is not available.

It is possible to add further flags after the S for use by the caller:

relax
Relax checking of some root certificate requirements. As of now this flag allows the use of root certificates with a missing basicConstraints attribute (despite that it is a MUST for CA certificates) and disables CRL checking for the root certificate.
cm
If validation of a certificate finally issued by a CA with this flag set fails, try again using the chain validation model.

sshcontrol
This file is used when support for the secure shell agent protocol has been enabled (see option –enable-ssh-support). Only keys present in this file are used in the SSH protocol. You should backup this file.

The ssh-add tool may be used to add new entries to this file; you may also add them manually. Comment lines, indicated by a leading hash mark, as well as empty lines are ignored. An entry starts with optional whitespace, followed by the keygrip of the key given as 40 hex digits, optionally followed by the caching TTL in seconds and another optional field for arbitrary flags. A non-zero TTL overrides the global default as set by --default-cache-ttl-ssh.

The only flag support is confirm. If this flag is found for a key, each use of the key will pop up a pinentry to confirm the use of that key. The flag is automatically set if a new key was loaded into gpg-agent using the option -c of the ssh-add command.

The keygrip may be prefixed with a ! to disable an entry entry.

The following example lists exactly one key. Note that keys available through a OpenPGP smartcard in the active smartcard reader are implicitly added to this list; i.e. there is no need to list them.

            # Key added on: 2011-07-20 20:38:46
            # Fingerprint:  5e:8d:c4:ad:e7:af:6e:27:8a:d6:13:e4:79:ad:0b:81
            34B62F25E277CF13D3C6BCEBFD3F85D08F0A864B 0 confirm

private-keys-v1.d/
This is the directory where gpg-agent stores the private keys. Each key is stored in a file with the name made up of the keygrip and the suffix key. You should backup all files in this directory and take great care to keep this backup closed away.

Note that on larger installations, it is useful to put predefined files into the directory /etc/skel/.gnupg/ so that newly created users start up with a working configuration. For existing users the a small helper script is provided to create these files (see addgnupghome).