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@c Copyright (C) 2002 Free Software Foundation, Inc.
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@c This is part of the GnuPG manual.
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@c For copying conditions, see the file gnupg.texi.
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@node Invoking GPG-AGENT
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@chapter Invoking GPG-AGENT
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@cindex GPG-AGENT command options
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@cindex command options
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@cindex options, GPG-AGENT command
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@c man begin DESCRIPTION
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@command{gpg-agent} is a daemon to manage secret (private) keys
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independelty from any protocol. It is used as a backend for
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@command{gpg} and @command{gpgsm} as well as for a couple of other
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The usual way to run the agent is from the @code{~/.xsession} file:
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eval `gpg-agent --daemon`
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If you don't use an X server, you can also put this into your regular
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startup file @code{~/.profile} or @code{.bash_profile}. It is best not
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to run multiple instance of the @command{gpg-agent}, so you should make sure that
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only is running: @command{gpg-agent} uses an environment variable to inform
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clients about the communication parameters. You can write the
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content of this environment variable to a file so that you can test for
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a running agent. This short script may do the job:
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if test -f $HOME/.gpg-agent-info && \
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kill -0 `cut -d: -f 2 $HOME/.gpg-agent-info` 2>/dev/null; then
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GPG_AGENT_INFO=`cat $HOME/.gpg-agent-info`
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eval `gpg-agent --daemon`
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echo $GPG_AGENT_INFO >$HOME/.gpg-agent-info
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You should always add the following lines to your @code{.bashrc} or
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whatever initialization file is used for all shell invocations:
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It is important that this environment variable always reflects the
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output of the @code{tty} command. For W32 systems this option is not
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Please make sure that a proper pinentry program has been installed
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under the default filename (which is system dependant) or use the
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option @code{pinentry-pgm} to specify the full name of that program.
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It is often useful to install a symbolic link from the actual used
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pinentry (e.g. @file{/usr/bin/pinentry-gtk}) to the expected
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one (e.g. @file{/usr/bin/pinentry}).
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@xref{Option Index}, for an index to @command{GPG-AGENT}'s commands and options.
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* Agent Commands:: List of all commands.
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* Agent Options:: List of all options.
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* Agent Signals:: Use of some signals.
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* Agent Examples:: Some usage examples.
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* Agent Protocol:: The protocol the agent uses.
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Commands are not distinguished from options execpt for the fact that
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only one one command is allowed.
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Print the program version and licensing information. Not that you can
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abbreviate this command.
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Print a usage message summarizing the most usefule command-line options.
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Not that you can abbreviate this command.
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Print a list of all available options and commands. Not that you can
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abbreviate this command.
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Run in server mode and wait for commands on the @code{stdin}. The
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default mode is to create a socket and listen for commands there.
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Run the program in the background. This option is required to prevent
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it from being accidently running in the background. A common way to do
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$ eval `gpg-agent --daemon`
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@section Option Summary
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@item --options @var{file}
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Reads configuration from @var{file} instead of from the default
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per-user configuration file. The default configuration file is named
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@file{gpg-agent.conf} and expected in the @file{.gnupg} directory directly
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below the home directory of the user.
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@item --homedir @var{dir}
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Set the name of the home directory to @var{dir}. If his option is not
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used, the home directory defaults to @file{~/.gnupg}. It is only
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recognized when given on the command line. It also overrides any home
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directory stated through the environment variable @env{GNUPGHOME} or
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(on W32 systems) by means on the Registry entry
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@var{HKCU\Software\GNU\GnuPG:HomeDir}.
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Outputs additional information while running.
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You can increase the verbosity by giving several
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verbose commands to @sc{gpgsm}, such as @samp{-vv}.
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Try to be as quiet as possible.
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Don't invoke a pinentry or do any other thing requiring human interaction.
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@item --faked-system-time @var{epoch}
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@opindex faked-system-time
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This option is only useful for testing; it sets the system time back or
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forth to @var{epoch} which is the number of seconds elapsed since the year
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@item --debug-level @var{level}
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Select the debug level for investigating problems. @var{level} may be
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some basic debug messages
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more verbose debug messages
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even more detailed messages
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all of the debug messages you can get
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How these messages are mapped to the actual debugging flags is not
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specified and may change with newer releaes of this program. They are
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however carefully selected to best aid in debugging.
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@item --debug @var{flags}
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This option is only useful for debugging and the behaviour may change at
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any time without notice. FLAGS are bit encoded and may be given in
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usual C-Syntax. The currently defined bits are:
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X.509 or OpenPGP protocol related data
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values of big number integers
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low level crypto operations
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show memory statistics.
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write hashed data to files named @code{dbgmd-000*}
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trace Assuan protocol
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bypass all certificate validation
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Same as @code{--debug=0xffffffff}
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@item --debug-wait @var{n}
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When running in server mode, wait @var{n} seconds before entering the
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actual processing loop and print the pid. This gives time to attach a
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Don't detach the process from the console. This is manly usefule for
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Format the info output in daemon mode for use with the standard Bourne
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shell respective the C-shell . The default ist to guess it based on the
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environment variable @code{SHELL} which is in almost all cases
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Tell the pinentryo not to grab the keyboard and mouse. This option
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should in general not be used to avaoid X-sniffing attacks.
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@item --log-file @var{file}
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Append all logging output to @var{file}. This is very helpful in
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seeing what the agent actually does.
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Don't allow multiple connections. This option is in general not very
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@item --allow-mark-trusted
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@opindex allow-mark-trusted
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Allow clients to mark keys as trusted, i.e. put them into the
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@code{trustlist.txt} file. This is by default not allowed to make it
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harder for users to inadvertly accept Root-CA keys.
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@item --ignore-cache-for-signing
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@opindex ignore-cache-for-signing
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This option will let @command{gpg-agent} bypass the passphrase cache for all
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signing operation. Note that there is also a per-session option to
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control this behaviour but this command line option takes precedence.
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@item --default-cache-ttl @var{n}
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@opindex default-cache-ttl
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Set the time a cache entry is valid to @var{n} seconds. The default are
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@item --max-cache-ttl @var{n}
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@opindex max-cache-ttl
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Set the maximum time a cache entry is valid to @var{n} seconds. After
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this time a cache entry will get expired even if it has been accessed
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recently. The default are 2 hours (7200 seconds).
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@item --pinentry-program @var{filename}
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@opindex pinentry-program
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Use program @var{filename} as the PIN entry. The default is installation
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dependend and can be shown with the @code{--version} command.
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@item --scdaemon-program @var{filename}
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@opindex scdaemon-program
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Use program @var{filename} as the Smartcard daemon. The default is
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installation dependend and can be shown with the @code{--version}
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@item --use-standard-socket
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@itemx --no-use-standard-socket
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@opindex use-standard-socket
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@opindex no-use-standard-socket
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By enabling this option @command{gpg-agent} will listen on the socket
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named @file{S.gpg-agent}, located in the home directory, and not create
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a random socket below a temporary directory. Tools connecting to
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@command{gpg-agent} should first try to connect to the socket given in
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environment variable @var{GPG_AGENT_INFO} and the fall back to this
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socket. This option may not be used if the home directory is mounted as
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a remote file system.
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Note, that as of now, W32 systems default to this option.
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@item --display @var{string}
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@itemx --ttyname @var{string}
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@itemx --ttytype @var{string}
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@itemx --lc-type @var{string}
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@itemx --lc-messages @var{string}
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These options are used with the server mode to pass localization
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@itemx --keep-display
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@opindex keep-display
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Ignore requests to change change the current @sc{tty} respective the X
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window system's @code{DISPLAY} variable. This is useful to lock the
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pinentry to pop up at the @sc{tty} or display you started the agent.
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All the long options may also be given in the configuration file after
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stripping off the two leading dashes.
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@section Use of some signals.
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A running @command{gpg-agent} may be controlled by signals, i.e. using
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the @command{kill} command to send a signal to the process.
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Here is a list of supported signals:
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This signals flushes all chached passphrases and when the program was
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started with a configuration file, the configuration file is read again.
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Only certain options are honored: @code{quiet}, @code{verbose},
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@code{debug}, @code{debug-all}, @code{no-grab}, @code{pinentry-program},
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@code{default-cache-ttl} and @code{ignore-cache-for-signing}.
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@code{scdaemon-program} is also supported but due to the current
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implementation, which calls the scdaemon only once, it is not of much
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Shuts down the process but waits until all current requests are
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fulfilled. If the process has received 3 of these signals and requests
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are still pending, a shutdown is forced.
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Shuts down the process immediately.
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These signals are used for internal purposes.
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@c man begin EXAMPLES
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$ eval `gpg-agent --daemon`
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@section Agent's Assuan Protocol
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The @command{gpg-agent} should be started by the login shell and set an
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environment variable to tell clients about the socket to be used.
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Clients should deny to access an agent with a socket name which does
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not match its own configuration. An application may choose to start
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an instance of the gpgagent if it does not figure that any has been
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started; it should not do this if a gpgagent is running but not
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usable. Because @command{gpg-agent} can only be used in background mode, no
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special command line option is required to activate the use of the
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To identify a key we use a thing called keygrip which is the SHA-1 hash
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of an canoncical encoded S-Expression of the the public key as used in
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Libgcrypt. For the purpose of this interface the keygrip is given as a
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hex string. The advantage of using this and not the hash of a
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certificate is that it will be possible to use the same keypair for
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different protocols, thereby saving space on the token used to keep the
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* Agent PKDECRYPT:: Decrypting a session key
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* Agent PKSIGN:: Signing a Hash
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* Agent GENKEY:: Generating a Key
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* Agent IMPORT:: Importing a Secret Key
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* Agent EXPORT:: Exporting a Secret Key
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* Agent ISTRUSTED:: Importing a Root Certificate
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* Agent GET_PASSPHRASE:: Ask for a passphrase
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* Agent GET_CONFIRMATION:: Ask for confirmation
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* Agent HAVEKEY:: Check whether a key is available
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* Agent LEARN:: Register a smartcard
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* Agent PASSWD:: Change a Passphrase
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@node Agent PKDECRYPT
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@subsection Decrypting a session key
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The client asks the server to decrypt a session key. The encrypted
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session key should have all information needed to select the
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appropriate secret key or to delegate it to a smartcard.
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Tell the server about the key to be used for decryption. If this is
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not used, @command{gpg-agent} may try to figure out the key by trying to
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decrypt the message with each key available.
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The agent checks whether this command is allowed and then does an
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INQUIRY to get the ciphertext the client should then send the cipher
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S: INQUIRE CIPHERTEXT
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Please note that the server may send status info lines while reading the
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data lines from the client. The data send is a SPKI like S-Exp with
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(<param_name1> <mpi>)
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(<param_namen> <mpi>)))
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Where algo is a string with the name of the algorithm; see the libgcrypt
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documentation for a list of valid algorithms. The number and names of
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the parameters depend on the algorithm. The agent does return an error
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if there is an inconsistency.
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If the decryption was successful the decrypted data is returned by
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Here is an example session:
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S: INQUIRE CIPHERTEXT
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C: D (enc-val elg (a 349324324)
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C: D (b 3F444677CA)))
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S: # session key follows
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S: D 1234567890ABCDEF0
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S: OK descryption successful
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@subsection Signing a Hash
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The client ask the agent to sign a given hash value. A default key
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will be chosen if no key has been set. To set a key a client first
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This can be used multiple times to create multiple signature, the list
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of keys is reset with the next PKSIGN command or a RESET. The server
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test whether the key is a valid key to sign something and responds with
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The client can use this command to tell the server about the data
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(which usually is a hash) to be signed.
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The actual signing is done using
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Options are not yet defined, but my later be used to choosen among
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different algorithms (e.g. pkcs 1.5)
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The agent does then some checks, asks for the passphrase and
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if SETHASH has not been used asks the client for the data to sign:
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C: D ABCDEF012345678901234
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As a result the server returns the signature as an SPKI like S-Exp
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(<param_name1> <mpi>)
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(<param_namen> <mpi>)))
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The operation is affected by the option
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OPTION use-cache-for-signing=0|1
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The default of @code{1} uses the cache. Setting this option to @code{0}
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will lead @command{gpg-agent} to ignore the passphrase cache. Note, that there is
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also a global command line option for @command{gpg-agent} to globally disable the
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Here is an example session:
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S: # I did ask the user whether he really wants to sign
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S: # I did ask the user for the passphrase
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C: D ABCDEF012345678901234
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S: # signature follows
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S: D (sig-val rsa (s 45435453654612121212))
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@subsection Generating a Key
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This is used to create a new keypair and store the secret key inside the
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active PSE -w which is in most cases a Soft-PSE. An not yet defined
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option allows to choose the storage location. To get the secret key out
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of the PSE, a special export tool has to be used.
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Invokes the key generation process and the server will then inquire
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on the generation parameters, like:
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C: D (genkey (rsa (nbits 1024)))
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The format of the key parameters which depends on the algorithm is of
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(parameter_name_1 ....)
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(parameter_name_n ....)))
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If everything succeeds, the server returns the *public key* in a SPKI
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like S-Expression like this:
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Here is an example session:
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C: D (genkey (rsa (nbits 1024)))
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S: D (rsa (n 326487324683264) (e 10001)))
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@subsection Importing a Secret Key
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This operation is not yet supportted by GpgAgent. Specialized tools
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are to be used for this.
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There is no actual need because we can expect that secret keys
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created by a 3rd party are stored on a smartcard. If we have
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generated the key ourself, we do not need to import it.
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@subsection Export a Secret Key
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Should be done by an extra tool.
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@node Agent ISTRUSTED
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@subsection Importing a Root Certificate
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Actually we do not import a Root Cert but provide a way to validate
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any piece of data by storing its Hash along with a description and
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an identifier in the PSE. Here is the interface desription:
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ISTRUSTED <fingerprint>
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Check whether the OpenPGP primary key or the X.509 certificate with the
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given fingerprint is an ultimately trusted key or a trusted Root CA
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certificate. The fingerprint should be given as a hexstring (without
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any blanks or colons or whatever in between) and may be left padded with
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00 in case of an MD5 fingerprint. GPGAgent will answer with:
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The key is in the table of trusted keys.
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ERR 304 (Not Trusted)
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The key is not in this table.
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Gpg needs the entire list of trusted keys to maintain the web of
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trust; the following command is therefore quite helpful:
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GpgAgent returns a list of trusted keys line by line:
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S: D 000000001234454556565656677878AF2F1ECCFF P
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S: D 340387563485634856435645634856438576457A P
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S: D FEDC6532453745367FD83474357495743757435D S
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The first item on a line is the hexified fingerprint where MD5
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ingerprints are @code{00} padded to the left and the second item is a
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flag to indicate the type of key (so that gpg is able to only take care
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of PGP keys). P = OpenPGP, S = S/MIME. A client should ignore the rest
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of the line, so that we can extend the format in the future.
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Finally a client should be able to mark a key as trusted:
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MARKTRUSTED @var{fingerprint} "P"|"S"
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The server will then pop up a window to ask the user whether she
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really trusts this key. For this it will probably ask for a text to
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be displayed like this:
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C: D Do you trust the key with the fingerprint @@FPR@@
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C: D bla fasel blurb.
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Known sequences with the pattern @@foo@@ are replaced according to this
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Format the fingerprint according to gpg rules for a v3 keys.
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Format the fingerprint according to gpg rules for a v4 keys.
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Choose an appropriate format to format the fingerprint.
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Replaced by a single @code{@@}
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@node Agent GET_PASSPHRASE
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@subsection Ask for a passphrase
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This function is usually used to ask for a passphrase to be used for
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conventional encryption, but may also be used by programs which need
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special handling of passphrases. This command uses a syntax which helps
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clients to use the agent with minimum effort.
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GET_PASSPHRASE @var{cache_id} [@var{error_message} @var{prompt} @var{description}]
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@var{cache_id} is expected to be a hex string used for caching a
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passphrase. Use a @code{X} to bypass the cache. With no other
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arguments the agent returns a cached passphrase or an error.
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@var{error_message} is either a single @code{X} for no error message or
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a string to be shown as an error message like (e.g. "invalid
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passphrase"). Blanks must be percent escaped or replaced by @code{+}'.
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@var{prompt} is either a single @code{X} for a default prompt or the
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text to be shown as the prompt. Blanks must be percent escaped or
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replaced by @code{+}.
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@var{description} is a text shown above the entry field. Blanks must be
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percent escaped or replaced by @code{+}.
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The agent either returns with an error or with a OK followed by the
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hex encoded passphrase. Note that the length of the strings is
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implicitly limited by the maximum length of a command.
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CLEAR_PASSPHRASE @var{cache_id}
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may be used to invalidate the cache entry for a passphrase. The
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function returns with OK even when there is no cached passphrase.
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@node Agent GET_CONFIRMATION
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@subsection Ask for confirmation
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This command may be used to ask for a simple confirmation by
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presenting a text and 2 bottonts: Okay and Cancel.
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GET_CONFIRMATION @var{description}
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@var{description}is displayed along with a Okay and Cancel
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button. Blanks must be percent escaped or replaced by @code{+}. A
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@code{X} may be used to display confirmation dialog with a default
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The agent either returns with an error or with a OK. Note, that the
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length of @var{description} is implicitly limited by the maximum
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@subsection Check whether a key is available
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This can be used to see whether a secret key is available. It does
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not return any information on whether the key is somehow protected.
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HAVEKEY @var{keygrip}
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The Agent answers either with OK or @code{No_Secret_Key} (208). The
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caller may want to check for other error codes as well.
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@subsection Register a smartcard
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This command is used to register a smartcard. With the --send
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option given the certificates are send back.
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@subsection Change a Passphrase
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This command is used to interactively change the passphrase of the key
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indentified by the hex string @var{keygrip}.
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doc/gpg-agent.texi
