Ubuntu Manpage: gpg-agent - Secret key management for GnuPG

Provided by: gnupg-agent_2.0.22-3ubuntu1.4_amd64

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 agent is usualy started on demand by gpg, gpgsm, gpgconf or gpg-connect-agent. Thus
there is no reason to start it manually. In case you want to use the included Secure
Shell Agent you may start the agent using:

gpg-connect-agent /bye

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
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. Note that you cannot
abbreviate this command.

--help

-h Print a usage message summarizing the most useful command-line options. Note that
you cannot abbreviate this command.

--dump-options
Print a list of all available options and commands. Note that you cannot
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. If neither a log file nor a log file descriptor has been set on a
Windows platform, the Registry entry HKCU\Software\GNU\GnuPG:DefaultLogFile, if
set, is used to specify the logging output.

--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.

--allow-loopback-pinentry
Allow clients to use the loopback pinentry features; see the option pinentry-mode
for details.

--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.

--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 gpgconf 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.

--disable-check-own-socket
gpg-agent employs a periodic self-test to detect a stolen socket. This usually
means a second instance of gpg-agent has taken over the socket and gpg-agent will
then terminate itself. This option may be used to disable this self-test for
debugging purposes.

--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 on a remote file
system which does not support special files like fifos or sockets. Note, that
--use-standard-socket is the default on all systems since GnuPG 2.1. Note, that
--use-standard-socket is the default on Windows systems. The default may be
changed at build time. It is possible to test at runtime whether the agent has
been configured for use with the standard socket by issuing the command gpg-agent
--use-standard-socket-p which returns success if the standard socket option has
been enabled.

--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 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:

gpg-connect-agent updatestartuptty /bye

Although all GnuPG components try to start the gpg-agent as needed, this is not possible
for the ssh support because ssh does not know about it. Thus if no GnuPG tool which
accesses the agent has been run, there is no guarantee that ssh is abale to use gpg-agent
for authentication. To fix this you may start gpg-agent if needed using this simple
command:

gpg-connect-agent /bye

Adding the --verbose shows the progress of starting the 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
           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. 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.

.RS 2
# 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
.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,  disable-scdaemon, and disable-check-own-socket.  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.