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 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.
- --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 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-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.
- --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 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:
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.
SEE ALSO¶
gpg2(1),
gpgsm(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.