NAME
gpg-agent - Secret key management for GnuPG
SYNOPSIS
gpg-agent [--homedir dir] [--options file] [options]
gpg-agent [--homedir dir] [--options file] [options] --server
gpg-agent [--homedir dir] [--options file] [options] --daemon
[command_line]
DESCRIPTION
gpg-agent is a daemon to manage secret (private) keys independently
from any protocol. It is used as a backend for gpg and gpgsm as well
as for a couple of other utilities.
The usual way to run the agent is from the ~/.xsession file:
eval $(gpg-agent --daemon)
If you don't use an X server, you can also put this into your regular
startup file ~/.profile or .bash_profile. It is best not to run
multiple instance of the gpg-agent, so you should make sure that only
one is running: gpg-agent uses an environment variable to inform
clients about the communication parameters. You can write the content
of this environment variable to a file so that you can test for a
running agent. Here is an example using Bourne shell syntax:
gpg-agent --daemon --enable-ssh-support \
--write-env-file "${HOME}/.gpg-agent-info"
This code should only be run once per user session to initially fire up
the agent. In the example the optional support for the included Secure
Shell agent is enabled and the information about the agent is written
to a file in the HOME directory. Note that by running gpg-agent
without arguments you may test whether an agent is already running;
however such a test may lead to a race condition, thus it is not
suggested.
The second script needs to be run for each interactive session:
if [ -f "${HOME}/.gpg-agent-info" ]; then
. "${HOME}/.gpg-agent-info"
export GPG_AGENT_INFO
export SSH_AUTH_SOCK
export SSH_AGENT_PID
fi
It reads the data out of the file and exports the variables. If you
don't use Secure Shell, you don't need the last two export statements.
You should always add the following lines to your .bashrc or whatever
initialization file is used for all shell invocations:
GPG_TTY=$(tty)
export GPG_TTY
It is important that this environment variable always reflects the
output of the tty command. For W32 systems this option is not
required.
Please make sure that a proper pinentry program has been installed
under the default filename (which is system dependant) or use the
option pinentry-program to specify the full name of that program. It
is often useful to install a symbolic link from the actual used
pinentry (e.g. '/usr/bin/pinentry-gtk') to the expected one (e.g.
'/usr/bin/pinentry').
COMMANDS
Commands are not distinguished from options except for the fact that
only one command is allowed.
--version
Print the program version and licensing information. Not that
you can abbreviate this command.
--help
-h Print a usage message summarizing the most useful command-line
options. Not that you can abbreviate this command.
--dump-options
Print a list of all available options and commands. Not that
you can abbreviate this command.
--server
Run in server mode and wait for commands on the stdin. The
default mode is to create a socket and listen for commands
there.
--daemon [command line]
Start the gpg-agent as a daemon; that is, detach it from the
console and run it in the background. Because gpg-agent prints
out important information required for further use, a common way
of invoking gpg-agent is: eval $(gpg-agent --daemon) to setup
the environment variables. The option --write-env-file is
another way commonly used to do this. Yet another way is
creating a new process as a child of gpg-agent: gpg-agent
--daemon /bin/sh. This way you get a new shell with the
environment setup properly; if you exit from this shell, gpg-
agent terminates as well.
OPTIONS
--options file
Reads configuration from file instead of from the default per-
user configuration file. The default configuration file is
named 'gpg-agent.conf' and expected in the '.gnupg' directory
directly below the home directory of the user.
--homedir dir
Set the name of the home directory to dir. If this option is not
used, the home directory defaults to '~/.gnupg'. It is only
recognized when given on the command line. It also overrides
any home directory stated through the environment variable
'GNUPGHOME' or (on W32 systems) by means of the Registry entry
HKCU\Software\GNU\GnuPG:HomeDir.
-v
--verbose
Outputs additional information while running. You can increase
the verbosity by giving several verbose commands to gpgsm, such
as '-vv'.
-q
--quiet
Try to be as quiet as possible.
--batch
Don't invoke a pinentry or do any other thing requiring human
interaction.
--faked-system-time epoch
This option is only useful for testing; it sets the system time
back or forth to epoch which is the number of seconds elapsed
since the year 1970.
--debug-level level
Select the debug level for investigating problems. level may be
a numeric value or a keyword:
none No debugging at all. A value of less than 1 may be used
instead of the keyword.
basic Some basic debug messages. A value between 1 and 2 may
be used instead of the keyword.
advanced
More verbose debug messages. A value between 3 and 5 may
be used instead of the keyword.
expert Even more detailed messages. A value between 6 and 8 may
be used instead of the keyword.
guru All of the debug messages you can get. A value greater
than 8 may be used instead of the keyword. The creation
of hash tracing files is only enabled if the keyword is
used.
How these messages are mapped to the actual debugging flags is not
specified and may change with newer releases of this program. They are
however carefully selected to best aid in debugging.
--debug flags
This option is only useful for debugging and the behaviour may
change at any time without notice. FLAGS are bit encoded and
may be given in usual C-Syntax. The currently defined bits are:
0 (1) X.509 or OpenPGP protocol related data
1 (2) values of big number integers
2 (4) low level crypto operations
5 (32) memory allocation
6 (64) caching
7 (128)
show memory statistics.
9 (512)
write hashed data to files named dbgmd-000*
10 (1024)
trace Assuan protocol
12 (4096)
bypass all certificate validation
--debug-all
Same as --debug=0xffffffff
--debug-wait n
When running in server mode, wait n seconds before entering the
actual processing loop and print the pid. This gives time to
attach a debugger.
--no-detach
Don't detach the process from the console. This is mainly
useful for debugging.
-s
--sh
-c
--csh Format the info output in daemon mode for use with the standard
Bourne shell or the C-shell respectively. The default is to
guess it based on the environment variable SHELL which is
correct in almost all cases.
--write-env-file file
Often it is required to connect to the agent from a process not
being an inferior of gpg-agent and thus the environment variable
with the socket name is not available. To help setting up those
variables in other sessions, this option may be used to write
the information into file. If file is not specified the default
name '${HOME}/.gpg-agent-info' will be used. The format is
suitable to be evaluated by a Bourne shell like in this simple
example:
eval $(cat file)
eval $(cut -d= -f 1 < file | xargs echo export)
--no-grab
Tell the pinentry not to grab the keyboard and mouse. This
option should in general not be used to avoid X-sniffing
attacks.
--log-file file
Append all logging output to file. This is very helpful in
seeing what the agent actually does.
--allow-mark-trusted
Allow clients to mark keys as trusted, i.e. put them into the
'trustlist.txt' file. This is by default not allowed to make it
harder for users to inadvertently accept Root-CA keys.
--ignore-cache-for-signing
This option will let gpg-agent bypass the passphrase cache for
all signing operation. Note that there is also a per-session
option to control this behaviour but this command line option
takes precedence.
--default-cache-ttl n
Set the time a cache entry is valid to n seconds. The default
is 600 seconds.
--default-cache-ttl-ssh n
Set the time a cache entry used for SSH keys is valid to n
seconds. The default is 1800 seconds.
--max-cache-ttl n
Set the maximum time a cache entry is valid to n seconds. After
this time a cache entry will be expired even if it has been
accessed recently. The default is 2 hours (7200 seconds).
--max-cache-ttl-ssh n
Set the maximum time a cache entry used for SSH keys is valid to
n seconds. After this time a cache entry will be expired even
if it has been accessed recently. The default is 2 hours (7200
seconds).
--enforce-passphrase-constraints
Enforce the passphrase constraints by not allowing the user to
bypass them using the ``Take it anyway'' button.
--min-passphrase-len n
Set the minimal length of a passphrase. When entering a new
passphrase shorter than this value a warning will be displayed.
Defaults to 8.
--min-passphrase-nonalpha n
Set the minimal number of digits or special characters required
in a passphrase. When entering a new passphrase with less than
this number of digits or special characters a warning will be
displayed. Defaults to 1.
--check-passphrase-pattern file
Check the passphrase against the pattern given in file. When
entering a new passphrase matching one of these pattern a
warning will be displayed. file should be an absolute filename.
The default is not to use any pattern file.
Security note: It is known that checking a passphrase against a
list of pattern or even against a complete dictionary is not
very effective to enforce good passphrases. Users will soon
figure up ways to bypass such a policy. A better policy is to
educate users on good security behavior and optionally to run a
passphrase cracker regularly on all users passphrases to catch
the very simple ones.
--max-passphrase-days n
Ask the user to change the passphrase if n days have passed
since the last change. With --enforce-passphrase-constraints
set the user may not bypass this check.
--enable-passphrase-history
This option does nothing yet.
--pinentry-program filename
Use program filename as the PIN entry. The default is
installation dependent and can be shown with the --version
command.
--pinentry-touch-file filename
By default the filename of the socket gpg-agent is listening for
requests is passed to Pinentry, so that it can touch that file
before exiting (it does this only in curses mode). This option
changes the file passed to Pinentry to filename. The special
name /dev/null may be used to completely disable this feature.
Note that Pinentry will not create that file, it will only
change the modification and access time.
--scdaemon-program filename
Use program filename as the Smartcard daemon. The default is
installation dependent and can be shown with the --version
command.
--disable-scdaemon
Do not make use of the scdaemon tool. This option has the
effect of disabling the ability to do smartcard operations.
Note, that enabling this option at runtime does not kill an
already forked scdaemon.
--use-standard-socket
--no-use-standard-socket
By enabling this option gpg-agent will listen on the socket
named 'S.gpg-agent', located in the home directory, and not
create a random socket below a temporary directory. Tools
connecting to gpg-agent should first try to connect to the
socket given in environment variable GPG_AGENT_INFO and then
fall back to this socket. This option may not be used if the
home directory is mounted as a remote file system. Note, that
--use-standard-socket is the default on Windows systems.
--display string
--ttyname string
--ttytype string
--lc-ctype string
--lc-messages string
--xauthority string
These options are used with the server mode to pass localization
information.
--keep-tty
--keep-display
Ignore requests to change the current tty or X window system's
DISPLAY variable respectively. This is useful to lock the
pinentry to pop up at the tty or display you started the agent.
--enable-ssh-support
Enable emulation of the OpenSSH Agent protocol.
In this mode of operation, the agent does not only implement the
gpg-agent protocol, but also the agent protocol used by OpenSSH
(through a separate socket). Consequently, it should be
possible to use the gpg-agent as a drop-in replacement for the
well known ssh-agent.
SSH Keys, which are to be used through the agent, need to be
added to the gpg-agent initially through the ssh-add utility.
When a key is added, ssh-add will ask for the password of the
provided key file and send the unprotected key material to the
agent; this causes the gpg-agent to ask for a passphrase, which
is to be used for encrypting the newly received key and storing
it in a gpg-agent specific directory.
Once a key has been added to the gpg-agent this way, the gpg-
agent will be ready to use the key.
Note: in case the gpg-agent receives a signature request, the
user might need to be prompted for a passphrase, which is
necessary for decrypting the stored key. Since the ssh-agent
protocol does not contain a mechanism for telling the agent on
which display/terminal it is running, gpg-agent's ssh-support
will use the TTY or X display where gpg-agent has been started.
To switch this display to the current one, the following command
may be used:
echo UPDATESTARTUPTTY | gpg-connect-agent
All the long options may also be given in the configuration file after
stripping off the two leading dashes.
EXAMPLES
The usual way to invoke gpg-agent is
$ eval $(gpg-agent --daemon)
An alternative way is by replacing ssh-agent with gpg-agent. If for
example ssh-agent is started as part of the Xsession initialization,
you may simply replace ssh-agent by a script like:
#!/bin/sh
exec /usr/local/bin/gpg-agent --enable-ssh-support --daemon \
--write-env-file ${HOME}/.gpg-agent-info "$@"
and add something like (for Bourne shells)
if [ -f "${HOME}/.gpg-agent-info" ]; then
. "${HOME}/.gpg-agent-info"
export GPG_AGENT_INFO
export SSH_AUTH_SOCK
export SSH_AGENT_PID
fi
to your shell initialization file (e.g. '~/.bashrc').
FILES
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:
.RS 2
# 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
.fi
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. This is for
example required if the certificate is missing the basicConstraints
attribute (despite that it is a MUST for CA certificates).
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 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.
.RS 2
# Key added on 2005-02-25 15:08:29
5A6592BF45DC73BD876874A28FD4639282E29B52 0
.fi
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]).
SIGNALS
A running gpg-agent may be controlled by signals, i.e. using the kill
command to send a signal to the process.
Here is a list of supported signals:
SIGHUP This signal flushes all cached passphrases and if the program
has been started with a configuration file, the configuration
file is read again. Only certain options are honored: quiet,
verbose, debug, debug-all, debug-level, no-grab, pinentry-
program, default-cache-ttl, max-cache-ttl, ignore-cache-for-
signing, allow-mark-trusted and disable-scdaemon. scdaemon-
program is also supported but due to the current implementation,
which calls the scdaemon only once, it is not of much use unless
you manually kill the scdaemon.
SIGTERM
Shuts down the process but waits until all current requests are
fulfilled. If the process has received 3 of these signals and
requests are still pending, a shutdown is forced.
SIGINT Shuts down the process immediately.
SIGUSR1
Dump internal information to the log file.
SIGUSR2
This signal is used for internal purposes.
SEE ALSO
gpg2(1), gpgsm(1), gpg-connect-agent(1), scdaemon(1)
The full documentation for this tool is maintained as a Texinfo manual.
If GnuPG and the info program are properly installed at your site, the
command
info gnupg
should give you access to the complete manual including a menu
structure and an index.