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GPG-AGENT(1) GNU Privacy Guard 2.1 GPG-AGENT(1)

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 [com‐
mand_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 automatically 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

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 out‐
put 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 dependent) 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 pinen‐
try (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.

As an alternative you may create 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; after you exit from
this shell, gpg-agent terminates within a few seconds.

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 Windows systems) by means of the Registry
entry HKCU\Software\GNU\GnuPG:HomeDir.

On Windows systems it is possible to install GnuPG as a portable
application. In this case only this command line option is con‐
sidered, all other ways to set a home directory are ignored.

To install GnuPG as a portable application under Windows, create
an empty file name ‘gpgconf.ctl’ in the same directory as the
tool ‘gpgconf.exe’. The root of the installation is than that
directory; or, if ‘gpgconf.exe’ has been installed directly
below a directory named ‘bin’, its parent directory. You also
need to make sure that the following directories exist and are
writable: ‘ROOT/home’ for the GnuPG home and
‘ROOT/var/cache/gnupg2’ for internal cache files.

-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.

–debug-quick-random
This option inhibits the use of the very secure random quality
level (Libgcrypt’s GCRY_VERY_STRONG_RANDOM) and degrades all
request down to standard random quality. It is only used for
testing and shall not be used for any production quality keys.
This option is only effective when given on the command line.

–debug-pinentry
This option enables extra debug information pertaining to the
Pinentry. As of now it is only useful when used along with
–debug 1024.

–no-detach
Don’t detach the process from the console. This is mainly use‐
ful 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 cor‐
rect in almost all cases.

–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 see‐
ing what the agent actually does. If neither a log file nor a
log file descriptor has been set on a Windows platform, the Reg‐
istry entry HKCU\Software\GNU\GnuPG:DefaultLogFile, if set, is
used to specify the logging output.

–no-allow-mark-trusted
Do not allow clients to mark keys as trusted, i.e. put them into
the ‘trustlist.txt’ file. This makes it harder for users to
inadvertently accept Root-CA keys.

–allow-preset-passphrase
This option allows the use of gpg-preset-passphrase to seed the
internal cache of gpg-agent with passphrases.

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

–no-allow-external-cache
Tell Pinentry not to enable features which use an external cache
for passphrases.

Some desktop environments prefer to unlock all credentials with
one master password and may have installed a Pinentry which
employs an additional external cache to implement such a policy.
By using this option the Pinentry is advised not to make use of
such a cache and instead always ask the user for the requested
passphrase.

–allow-emacs-pinentry
Tell Pinentry to allow features to divert the passphrase entry
to a running Emacs instance. How this is exactly handled
depends on the version of the used Pinentry.

–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. Each time a cache entry is accessed, the
entry’s timer is reset. To set an entry’s maximum lifetime, use
max-cache-ttl.

–default-cache-ttl-ssh n
Set the time a cache entry used for SSH keys is valid to n sec‐
onds. The default is 1800 seconds. Each time a cache entry is
accessed, the entry’s timer is reset. To set an entry’s maximum
lifetime, use max-cache-ttl-ssh.

–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 or has been set using gpg-preset-passphrase.
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 or has been set using gpg-pre‐
set-passphrase. 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 warn‐
ing 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-invisible-char char
This option asks the Pinentry to use char for displaying hidden
characters. char must be one character UTF-8 string. A Pinen‐
try may or may not honor this request.

–pinentry-timeout n
This option asks the Pinentry to timeout after n seconds with no
user input. The default value of 0 does not ask the pinentry to
timeout, however a Pinentry may use its own default timeout
value in this case. A Pinentry may or may not honor this
request.

–pinentry-program filename
Use program filename as the PIN entry. The default is installa‐
tion dependent. With the default configuration the name of the
default pinentry is ‘pinentry’; if that file does not exist but
a ‘pinentry-basic’ exist the latter is used.

On a Windows platform the default is to use the first existing
program from this list: ‘bin\pinentry.exe’,
‘..\Gpg4win\bin\pinentry.exe’, ‘..\Gpg4win\pinentry.exe’,
‘..\GNU\GnuPG\pinentry.exe’, ‘..\GNU\bin\pinentry.exe’,
‘bin\pinentry-basic.exe’ where the file names are relative to
the GnuPG installation directory.

–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 com‐
mand.

–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

–use-standard-socket-p
Since GnuPG 2.1 the standard socket is always used. These
options have no more effect. The command gpg-agent –use-stan‐
dard-socket-p will thus always return success.

–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.

–extra-socket name
Also listen on native gpg-agent connections on the given socket.
The intended use for this extra socket is to setup a Unix domain
socket forwarding from a remote machine to this socket on the
local machine. A gpg running on the remote machine may then
connect to the local gpg-agent and use its private keys. This
allows to decrypt or sign data on a remote machine without
exposing the private keys to the remote machine.

–enable-ssh-support

–enable-putty-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 possi‐
ble 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 neces‐
sary for decrypting the stored key. Since the ssh-agent proto‐
col 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 able to use gpg-agent for authentica‐
tion. 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.

The –enable-putty-support is only available under Windows and allows
the use of gpg-agent with the ssh implementation putty. This is simi‐
lar to the regular ssh-agent support but makes use of Windows message
queue as required by putty.

All the long options may also be given in the configuration file after
stripping off the two leading dashes.

EXAMPLES
It is important to set the GPG_TTY environment variable in your login
shell, for example in the ‘~/.bashrc’ init script:

export GPG_TTY=$(tty)

If you enabled the Ssh Agent Support, you also need to tell ssh about
it by adding this to your init script:

unset SSH_AGENT_PID
if [ “${gnupg_SSH_AUTH_SOCK_by:-0}” -ne $$ ]; then
export SSH_AUTH_SOCK=”${HOME}/.gnupg/S.gpg-agent.ssh”
fi

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 abbre‐
viated.
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 disallowing interactive
updates of this file by using the see: [option –no-allow-mark-trusted].
It might even be 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/gnupg2/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 prede‐
fined files into the directory ‘/etc/skel/.gnupg2’ so that newly
created users start up with a working configuration. For exist‐
ing 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, debug-pinentry, no-grab,
pinentry-program, pinentry-invisible-char, default-cache-ttl,
max-cache-ttl, ignore-cache-for-signing, no-allow-external-
cache, allow-emacs-pinentry, no-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.

SEE ALSO

gpg2, gpgsm(1), gpg-connect-agent, 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 struc‐
ture and an index.

GnuPG 2.1.11 2016-01-21 GPG-AGENT(1)