gpg-agent - Secret key management for GnuPG
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]
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:
If you want to manually terminate the currently-running agent, you can safely do
so with:
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 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 pinentry (e.g. ‘
/usr/bin/pinentry-gtk’) to the expected one (e.g. ‘
/usr/bin/pinentry’).
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.
- --supervised
- Run in the foreground, sending logs by default to stderr,
and listening on provided file descriptors, which must already be bound to
listening sockets. This command is useful when running under systemd or
other similar process supervision schemes. This option is not supported on
Windows.
In --supervised mode, different file descriptors can be provided for use as
different socket types (e.g. ssh, extra) as long as they are identified in
the environment variable LISTEN_FDNAMES (see sd_listen_fds(3) on
some Linux distributions for more information on this convention).
Options may either be used on the command line or, after stripping off the two
leading dashes, in the configuration file.
- --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. This option is ignored if used in an options file.
- --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 considered, all
other ways to set a home directory are ignored.
To install GnuPG as a portable application under Windows, create an empty
file named ‘ gpgconf.ctl’ in the same directory as
the tool ‘ gpgconf.exe’. The root of the installation
is then 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/gnupg’ for internal cache files.
- -v
-
--verbose Outputs additional information while
running. You can increase the verbosity by giving several verbose commands
to gpg-agent, 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 behavior
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 should not be used for any production quality keys. This
option is only effective when given on the command line.
On GNU/Linux, another way to quickly generate insecure keys is to use
rngd to fill the kernel's entropy pool with lower quality random
data. rngd is typically provided by the rng-tools package.
It can be run as follows: ‘sudo rngd -f -r /dev/urandom’.
- --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
useful for debugging.
- --steal-socket
- In --daemon mode, gpg-agent detects an already
running gpg-agent and does not allow to start a new instance. This option
can be used to override this check: the new gpg-agent process will try to
take over the communication sockets from the already running process and
start anyway. This option should in general not be used.
- -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.
- --grab
-
--no-grab Tell the pinentry to grab the keyboard and
mouse. This option should be used on X-Servers to avoid X-sniffing
attacks. Any use of the option --grab overrides an used option
--no-grab. The default is --no-grab.
- --log-file file
- Append all logging output to file. This is very
helpful in seeing what the agent actually does. Use ‘
socket://’ to log to socket. 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.
- --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.
- --no-user-trustlist
- Entirely ignore the user trust list and consider only the
global trustlist (‘ /etc/gnupg/trustlist.txt’). This
implies the [option --no-allow-mark-trusted].
- --sys-trustlist-name file
- Changes the default name for the global trustlist from
"trustlist.txt" to file. If file does not contain
any slashes and does not start with "~/" it is searched in the
system configuration directory (‘ /etc/gnupg’).
- --allow-preset-passphrase
- This option allows the use of gpg-preset-passphrase
to seed the internal cache of gpg-agent with passphrases.
- --no-allow-loopback-pinentry
- --allow-loopback-pinentry
- Disallow or allow clients to use the loopback pinentry
features; see the option pinentry-mode for details. Allow is the
default.
The --force option of the Assuan command DELETE_KEY is also
controlled by this option: The option is ignored if a loopback pinentry is
disallowed.
- --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 behavior 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. Note that a cached passphrase may not be evicted
immediately from memory if no client requests a cache operation. This is
due to an internal housekeeping function which is only run every few
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. 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-preset-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-sym-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. If
file does not contain any slashes and does not start with
"~/" it is searched in the system configuration directory
(‘ /etc/gnupg’). The default is not to use any
pattern file. The second version of this option is only used when creating
a new symmetric key to allow the use of different patterns for such
passphrases.
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 Pinentry 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-formatted-passphrase
- This option asks the Pinentry to enable passphrase
formatting when asking the user for a new passphrase and masking of the
passphrase is turned off.
If passphrase formatting is enabled, then all non-breaking space characters
are stripped from the entered passphrase. Passphrase formatting is mostly
useful in combination with passphrases generated with the GENPIN feature
of some Pinentries. Note that such a generated passphrase, if not modified
by the user, skips all passphrase constraints checking because such
constraints would actually weaken the generated passphrase.
- --pinentry-program filename
- Use program filename as the PIN entry. The default
is installation 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
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
--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-standard-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.
- --listen-backlog n
- Set the size of the queue for pending connections. The
default is 64.
- --extra-socket name
- The extra socket is created by default, you may use this
option to change the name of the socket. To disable the creation of the
socket use ``none'' or ``/dev/null'' for 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 enables decrypting or signing
data on a remote machine without exposing the private keys to the remote
machine.
- --enable-extended-key-format
-
--disable-extended-key-format Since version 2.2.22
keys are created in the extended private key format by default. Changing
the passphrase of a key will also convert the key to that new format. This
key format is supported since GnuPG version 2.1.12 and thus there should
be no need to disable it. Anyway, the disable option still allows to
revert to the old behavior for new keys; be aware that keys are never
migrated back to the old format. If the enable option has been used the
disable option won't have an effect. The advantage of the extended private
key format is that it is text based and can carry additional meta data. In
extended key format the OCB mode is used for key protection.
- --enable-ssh-support
-
--enable-putty-support
The OpenSSH Agent protocol is always enabled, but gpg-agent will only
set the SSH_AUTH_SOCK variable if this flag is given.
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 able to use gpg-agent for authentication. To fix this you may start
gpg-agent if needed using this simple command:
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 similar to
the regular ssh-agent support but makes use of Windows message queue as
required by
putty.
- --ssh-fingerprint-digest
-
Select the digest algorithm used to compute ssh fingerprints that are
communicated to the user, e.g. in pinentry dialogs. OpenSSH has
transitioned from using MD5 to the more secure SHA256.
- --auto-expand-secmem n
- Allow Libgcrypt to expand its secure memory area as
required. The optional value n is a non-negative integer with a
suggested size in bytes of each additionally allocated secure memory area.
The value is rounded up to the next 32 KiB; usual C style prefixes are
allowed. For an heavy loaded gpg-agent with many concurrent connection
this option avoids sign or decrypt errors due to out of secure memory
error returns.
- --s2k-calibration milliseconds
- Change the default calibration time to milliseconds.
The given value is capped at 60 seconds; a value of 0 resets to the
compiled-in default. This option is re-read on a SIGHUP (or gpgconf
--reload gpg-agent) and the S2K count is then re-calibrated.
- --s2k-count n
- Specify the iteration count used to protect the passphrase.
This option can be used to override the auto-calibration done by default.
The auto-calibration computes a count which requires by default 100ms to
mangle a given passphrase. See also --s2k-calibration.
To view the actually used iteration count and the milliseconds required for
an S2K operation use:
gpg-connect-agent 'GETINFO s2k_count' /bye
gpg-connect-agent 'GETINFO s2k_time' /bye
To view the auto-calibrated count use:
gpg-connect-agent 'GETINFO s2k_count_cal' /bye
It is important to set the environment variable
GPG_TTY in your login
shell, for example in the ‘
~/.bashrc’ init script:
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="$(gpgconf --list-dirs agent-ssh-socket)"
fi
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
enables cutting and pasting 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 [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/gnupg/trustlist.txt’).
This global list is also used if the local list is not available;
the [option --no-user-trustlist] enforces the use of only
this global list.
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.
The following example lists exactly one key. Note that keys available
through a OpenPGP smartcard in the active smartcard reader are
implicitly added to this list; i.e. there is no need to list them.
# Key added on: 2011-07-20 20:38:46
# Fingerprint: 5e:8d:c4:ad:e7:af:6e:27:8a:d6:13:e4:79:ad:0b:81
34B62F25E277CF13D3C6BCEBFD3F85D08F0A864B 0 confirm
- private-keys-v1.d/
-
This is the directory where gpg-agent stores the private keys. Each
key is stored in a file with the name made up of the keygrip and the
suffix ‘ key’. You should backup all files in this
directory
and take great care to keep this backup closed away.
Note that on larger installations, it is useful to put predefined files into the
directory ‘
/etc/skel/.gnupg’ so that newly created users
start up with a working configuration. For existing users the a small helper
script is provided to create these files (see: [addgnupghome]).
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, s2k-count,
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.
gpg(1),
gpgsm(1),
gpgconf(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
should give you access to the complete manual including a menu structure and an
index.