GPG-AGENT

Section: GNU Privacy Guard 2.2 (1)
Updated: 2021-03-22
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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 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

If you want to manually terminate the currently-running agent, you can safely do so with:

gpgconf --kill gpg-agent

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/local/bin/pinentry-gtk') to the expected one (e.g. '/usr/local/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.

--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

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/usr/local/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

Set debug flags. All flags are or-ed and flags may be given in C syntax (e.g. 0x0042) or as a comma separated list of flag names. To get a list of all supported flags the single word "help" can be used. This option is only useful for debugging and the behavior may change at any time without notice.

--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.

-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.

--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 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-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-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 2.3 keys are created in the extended private key format. Changing the passphrase of a key will also convert the key to that new format. This new key format is supported since GnuPG version 2.1.12 and thus there should be no need to disable it. The disable option allows to revert to the old behavior for new keys; be aware that keys are never migrated back to the old format. However 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.

--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:

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 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

EXAMPLES

It is important to set the environment variable GPG_TTY 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="$(gpgconf --list-dirs agent-ssh-socket)"
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 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. '/usr/local/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.

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 '/usr/local/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, 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.