gnupg/doc/gpg-agent.texi

@c Copyright (C) 2002 Free Software Foundation, Inc.
@c This is part of the GnuPG manual.
@c For copying conditions, see the file gnupg.texi.

@c Note that we use this texinfo file for all versions of GnuPG:
@c 2.0 and 2.1.  The macro "gpgtwoone" controls parts which are only
@c valid for GnuPG 2.1 and later.


@node Invoking GPG-AGENT
@chapter Invoking GPG-AGENT
@cindex GPG-AGENT command options
@cindex command options
@cindex options, GPG-AGENT command

@manpage gpg-agent.1
@ifset manverb
.B gpg-agent
\- Secret key management for GnuPG
@end ifset

@mansect synopsis
@ifset manverb
.B  gpg-agent
.RB [ \-\-homedir
.IR dir ]
.RB [ \-\-options
.IR file ]
.RI [ options ]
.br
.B  gpg-agent
.RB [ \-\-homedir
.IR dir ]
.RB [ \-\-options
.IR file ]
.RI [ options ]
.B  \-\-server
.br
.B  gpg-agent
.RB [ \-\-homedir
.IR dir ]
.RB [ \-\-options
.IR file ]
.RI [ options ]
.B  \-\-daemon
.RI [ command_line ]
@end ifset

@mansect description
@command{gpg-agent} is a daemon to manage secret (private) keys
independently from any protocol.  It is used as a backend for
@command{gpg} and @command{gpgsm} as well as for a couple of other
utilities.

@ifset gpgtwoone
The agent is usualy started on demand by @command{gpg}, @command{gpgsm},
@command{gpgconf} or @command{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:

@example
gpg-connect-agent /bye
@end example
@end ifset

@ifclear gpgtwoone
@noindent
The usual way to run the agent is from the @code{~/.xsession} file:

@example
eval $(gpg-agent --daemon)
@end example
@noindent
If you don't use an X server, you can also put this into your regular
startup file @code{~/.profile} or @code{.bash_profile}.  It is best not
to run multiple instance of the @command{gpg-agent}, so you should make
sure that only one is running: @command{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:

@smallexample
gpg-agent --daemon --enable-ssh-support \
          --write-env-file "$@{HOME@}/.gpg-agent-info"
@end smallexample

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.

@noindent
The second script needs to be run for each interactive session:

@smallexample
if [ -f "$@{HOME@}/.gpg-agent-info" ]; then
  . "$@{HOME@}/.gpg-agent-info"
  export GPG_AGENT_INFO
  export SSH_AUTH_SOCK
fi
@end smallexample

@noindent
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.
@end ifclear

@noindent
You should always add the following lines to your @code{.bashrc} or
whatever initialization file is used for all shell invocations:

@smallexample
GPG_TTY=$(tty)
export GPG_TTY
@end smallexample

@noindent
It is important that this environment variable always reflects the
output of the @code{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 @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. @file{/usr/bin/pinentry-gtk}) to the expected
one (e.g. @file{/usr/bin/pinentry}).

@manpause
@noindent
@xref{Option Index},for an index to @command{GPG-AGENT}'s commands and options.
@mancont

@menu
* Agent Commands::      List of all commands.
* Agent Options::       List of all options.
* Agent Configuration:: Configuration files.
* Agent Signals::       Use of some signals.
* Agent Examples::      Some usage examples.
* Agent Protocol::      The protocol the agent uses.
@end menu

@mansect commands
@node Agent Commands
@section Commands

Commands are not distinguished from options except for the fact that
only one command is allowed.

@table @gnupgtabopt
@item --version
@opindex version
Print the program version and licensing information.  Note that you cannot
abbreviate this command.

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

@item --dump-options
@opindex dump-options
Print a list of all available options and commands.  Note that you cannot
abbreviate this command.

@item --server
@opindex server
Run in server mode and wait for commands on the @code{stdin}.  The
default mode is to create a socket and listen for commands there.

@item --daemon [@var{command line}]
@opindex daemon
Start the gpg-agent as a daemon; that is, detach it from the console
and run it in the background.  Because @command{gpg-agent} prints out
important information required for further use, a common way of
invoking gpg-agent is: @code{eval $(gpg-agent --daemon)} to setup the
environment variables.  The option @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: @code{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.
@end table

@mansect options
@node Agent Options
@section Option Summary

@table @gnupgtabopt

@anchor{option --options}
@item --options @var{file}
@opindex options
Reads configuration from @var{file} instead of from the default
per-user configuration file.  The default configuration file is named
@file{gpg-agent.conf} and expected in the @file{.gnupg} directory directly
below the home directory of the user.

@anchor{option --homedir}
@include opt-homedir.texi


@item -v
@item --verbose
@opindex verbose
Outputs additional information while running.
You can increase the verbosity by giving several
verbose commands to @command{gpgsm}, such as @samp{-vv}.

@item -q
@item --quiet
@opindex quiet
Try to be as quiet as possible.

@item --batch
@opindex batch
Don't invoke a pinentry or do any other thing requiring human interaction.

@item --faked-system-time @var{epoch}
@opindex faked-system-time
This option is only useful for testing; it sets the system time back or
forth to @var{epoch} which is the number of seconds elapsed since the year
1970.

@item --debug-level @var{level}
@opindex debug-level
Select the debug level for investigating problems. @var{level} may be
a numeric value or a keyword:

@table @code
@item none
No debugging at all.  A value of less than 1 may be used instead of
the keyword.
@item basic
Some basic debug messages.  A value between 1 and 2 may be used
instead of the keyword.
@item advanced
More verbose debug messages.  A value between 3 and 5 may be used
instead of the keyword.
@item expert
Even more detailed messages.  A value between 6 and 8 may be used
instead of the keyword.
@item 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.
@end table

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.

@item --debug @var{flags}
@opindex debug
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:

@table @code
@item 0  (1)
X.509 or OpenPGP protocol related data
@item 1  (2)
values of big number integers
@item 2  (4)
low level crypto operations
@item 5  (32)
memory allocation
@item 6  (64)
caching
@item 7  (128)
show memory statistics.
@item 9  (512)
write hashed data to files named @code{dbgmd-000*}
@item 10 (1024)
trace Assuan protocol
@item 12 (4096)
bypass all certificate validation
@end table

@item --debug-all
@opindex debug-all
Same as @code{--debug=0xffffffff}

@item --debug-wait @var{n}
@opindex debug-wait
When running in server mode, wait @var{n} seconds before entering the
actual processing loop and print the pid.  This gives time to attach a
debugger.

@item --no-detach
@opindex no-detach
Don't detach the process from the console.  This is mainly useful for
debugging.

@item -s
@itemx --sh
@itemx -c
@itemx --csh
@opindex sh
@opindex 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 @code{SHELL} which is correct in almost all
cases.

@item --write-env-file @var{file}
@opindex write-env-file
Often it is required to connect to the agent from a process not being an
inferior of @command{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
@var{file}.  If @var{file} is not specified the default name
@file{$@{HOME@}/.gpg-agent-info} will be used.  The format is suitable
to be evaluated by a Bourne shell like in this simple example:

@example
eval $(cat @var{file})
eval $(cut -d= -f 1 < @var{file} | xargs echo export)
@end example



@item --no-grab
@opindex 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.

@anchor{option --log-file}
@item --log-file @var{file}
@opindex log-file
Append all logging output to @var{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
@code{HKCU\Software\GNU\GnuPG:DefaultLogFile}, if set, is used to specify
the logging output.


@anchor{option --allow-mark-trusted}
@item --allow-mark-trusted
@opindex allow-mark-trusted
Allow clients to mark keys as trusted, i.e. put them into the
@file{trustlist.txt} file.  This is by default not allowed to make it
harder for users to inadvertently accept Root-CA keys.

@ifset gpgtwoone
@anchor{option --allow-loopback-pinentry}
@item --allow-loopback-pinentry
@opindex allow-loopback-pinentry
Allow clients to use the loopback pinentry features; see the option
@option{pinentry-mode} for details.
@end ifset

@item --ignore-cache-for-signing
@opindex ignore-cache-for-signing
This option will let @command{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.

@item --default-cache-ttl @var{n}
@opindex default-cache-ttl
Set the time a cache entry is valid to @var{n} seconds.  The default is
600 seconds.

@item --default-cache-ttl-ssh @var{n}
@opindex default-cache-ttl
Set the time a cache entry used for SSH keys is valid to @var{n}
seconds.  The default is 1800 seconds.

@item --max-cache-ttl @var{n}
@opindex max-cache-ttl
Set the maximum time a cache entry is valid to @var{n} seconds.  After
this time a cache entry will be expired even if it has been accessed
recently.  The default is 2 hours (7200 seconds).

@item --max-cache-ttl-ssh @var{n}
@opindex max-cache-ttl-ssh
Set the maximum time a cache entry used for SSH keys is valid to @var{n}
seconds.  After this time a cache entry will be expired even if it has
been accessed recently.  The default is 2 hours (7200 seconds).

@item --enforce-passphrase-constraints
@opindex enforce-passphrase-constraints
Enforce the passphrase constraints by not allowing the user to bypass
them using the ``Take it anyway'' button.

@item --min-passphrase-len @var{n}
@opindex min-passphrase-len
Set the minimal length of a passphrase.  When entering a new passphrase
shorter than this value a warning will be displayed.  Defaults to 8.

@item --min-passphrase-nonalpha @var{n}
@opindex min-passphrase-nonalpha
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.

@item --check-passphrase-pattern @var{file}
@opindex check-passphrase-pattern
Check the passphrase against the pattern given in @var{file}.  When
entering a new passphrase matching one of these pattern a warning will
be displayed. @var{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.

@item --max-passphrase-days @var{n}
@opindex max-passphrase-days
Ask the user to change the passphrase if @var{n} days have passed since
the last change.  With @option{--enforce-passphrase-constraints} set the
user may not bypass this check.

@item --enable-passphrase-history
@opindex enable-passphrase-history
This option does nothing yet.

@item --pinentry-program @var{filename}
@opindex pinentry-program
Use program @var{filename} as the PIN entry.  The default is installation
dependent.

@item --pinentry-touch-file @var{filename}
@opindex pinentry-touch-file
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 @var{filename}.  The special name
@code{/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.


@item --scdaemon-program @var{filename}
@opindex scdaemon-program
Use program @var{filename} as the Smartcard daemon.  The default is
installation dependent and can be shown with the @command{gpgconf}
command.

@item --disable-scdaemon
@opindex 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.

@item --use-standard-socket
@itemx --no-use-standard-socket
@opindex use-standard-socket
@opindex no-use-standard-socket
By enabling this option @command{gpg-agent} will listen on the socket
named @file{S.gpg-agent}, located in the home directory, and not create
a random socket below a temporary directory.  Tools connecting to
@command{gpg-agent} should first try to connect to the socket given in
environment variable @var{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.
@ifset gpgtwoone
Note, that @option{--use-standard-socket} is the default on all
systems since GnuPG 2.1.
@end ifset
@ifclear gpgtwoone
Note, that @option{--use-standard-socket} is the default on
Windows systems.
@end ifclear
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 @command{gpg-agent
--use-standard-socket-p} which returns success if the standard socket
option has been enabled.

@item --display @var{string}
@itemx --ttyname @var{string}
@itemx --ttytype @var{string}
@itemx --lc-ctype @var{string}
@itemx --lc-messages @var{string}
@itemx --xauthority @var{string}
@opindex display
@opindex ttyname
@opindex ttytype
@opindex lc-ctype
@opindex lc-messages
@opindex xauthority
These options are used with the server mode to pass localization
information.

@item --keep-tty
@itemx --keep-display
@opindex keep-tty
@opindex keep-display
Ignore requests to change the current @code{tty} or X window system's
@code{DISPLAY} variable respectively.  This is useful to lock the
pinentry to pop up at the @code{tty} or display you started the agent.

@anchor{option --enable-ssh-support}
@item --enable-ssh-support
@opindex 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:

@smallexample
gpg-connect-agent updatestartuptty /bye
@end smallexample

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:

@smallexample
gpg-connect-agent /bye
@end smallexample

Adding the @option{--verbose} shows the progress of starting the agent.

@end table

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


@mansect files
@node Agent Configuration
@section Configuration

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
(@pxref{option --homedir}).

@table @file

@item gpg-agent.conf
@cindex gpg-agent.conf
  This is the standard configuration file read by @command{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 @code{SIGHUP} however only a few
  options will actually have an effect.  This default name may be
  changed on the command line (@pxref{option --options}).
  You should backup this file.

@item 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 @code{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 @code{!} 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:

  @example
  # 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
  @end example

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 @xref{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 @code{include-default} will include a global
list of trusted certificates (e.g. @file{/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 @code{S} for use by the
caller:

@table @code

@item relax
@cindex 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.

@item cm
If validation of a certificate finally issued by a CA with this flag set
fails, try again using the chain validation model.

@end table


@item sshcontrol
@cindex sshcontrol
This file is used when support for the secure shell agent protocol has
been enabled (@pxref{option --enable-ssh-support}). Only keys present in
this file are used in the SSH protocol.  You should backup this file.

The @command{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 @option{--default-cache-ttl-ssh}.

The only flag support is @code{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
@code{gpg-agent} using the option @option{-c} of the @code{ssh-add}
command.

The keygrip may be prefixed with a @code{!} 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.

  @example
  # 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
  @end example

@item 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 @file{key}.  You should backup all files in this directory
  and take great care to keep this backup closed away.


@end table

Note that on larger installations, it is useful to put predefined
files into the directory @file{/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 (@pxref{addgnupghome}).



@c
@c Agent Signals
@c
@mansect signals
@node Agent Signals
@section Use of some signals.
A running @command{gpg-agent} may be controlled by signals, i.e. using
the @command{kill} command to send a signal to the process.

Here is a list of supported signals:

@table @gnupgtabopt

@item SIGHUP
@cpindex 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: @code{quiet}, @code{verbose},
@code{debug}, @code{debug-all}, @code{debug-level}, @code{no-grab},
@code{pinentry-program}, @code{default-cache-ttl}, @code{max-cache-ttl},
@code{ignore-cache-for-signing}, @code{allow-mark-trusted} and
@code{disable-scdaemon}.  @code{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.


@item SIGTERM
@cpindex 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.

@item SIGINT
@cpindex SIGINT
Shuts down the process immediately.

@item SIGUSR1
@cpindex SIGUSR1
Dump internal information to the log file.

@item SIGUSR2
@cpindex SIGUSR2
This signal is used for internal purposes.

@end table

@c
@c  Examples
@c
@mansect examples
@node Agent Examples
@section Examples

The usual way to invoke @command{gpg-agent} is

@example
$ eval $(gpg-agent --daemon)
@end example

An alternative way is by replacing @command{ssh-agent} with
@command{gpg-agent}.  If for example @command{ssh-agent} is started as
part of the Xsession initialization, you may simply replace
@command{ssh-agent} by a script like:

@cartouche
@example
#!/bin/sh

exec /usr/local/bin/gpg-agent --enable-ssh-support --daemon \
      --write-env-file $@{HOME@}/.gpg-agent-info "$@@"
@end example
@end cartouche

@noindent
and add something like (for Bourne shells)

@cartouche
@example
  if [ -f "$@{HOME@}/.gpg-agent-info" ]; then
    . "$@{HOME@}/.gpg-agent-info"
    export GPG_AGENT_INFO
    export SSH_AUTH_SOCK
  fi
@end example
@end cartouche

@noindent
to your shell initialization file (e.g. @file{~/.bashrc}).

@c
@c  Assuan Protocol
@c
@manpause
@node Agent Protocol
@section Agent's Assuan Protocol

Note: this section does only document the protocol, which is used by
GnuPG components; it does not deal with the ssh-agent protocol.

The @command{gpg-agent} should be started by the login shell and set an
environment variable to tell clients about the socket to be used.
Clients should deny to access an agent with a socket name which does
not match its own configuration.  An application may choose to start
an instance of the gpgagent if it does not figure that any has been
started; it should not do this if a gpgagent is running but not
usable.  Because @command{gpg-agent} can only be used in background mode, no
special command line option is required to activate the use of the
protocol.

To identify a key we use a thing called keygrip which is the SHA-1 hash
of an canonical encoded S-Expression of the public key as used in
Libgcrypt.  For the purpose of this interface the keygrip is given as a
hex string.  The advantage of using this and not the hash of a
certificate is that it will be possible to use the same keypair for
different protocols, thereby saving space on the token used to keep the
secret keys.

@menu
* Agent PKDECRYPT::       Decrypting a session key
* Agent PKSIGN::          Signing a Hash
* Agent GENKEY::          Generating a Key
* Agent IMPORT::          Importing a Secret Key
* Agent EXPORT::          Exporting a Secret Key
* Agent ISTRUSTED::       Importing a Root Certificate
* Agent GET_PASSPHRASE::  Ask for a passphrase
* Agent GET_CONFIRMATION:: Ask for confirmation
* Agent HAVEKEY::         Check whether a key is available
* Agent LEARN::           Register a smartcard
* Agent PASSWD::          Change a Passphrase
* Agent UPDATESTARTUPTTY:: Change the Standard Display
* Agent GETEVENTCOUNTER:: Get the Event Counters
* Agent GETINFO::         Return information about the process
* Agent OPTION::          Set options for the session
@end menu

@node Agent PKDECRYPT
@subsection Decrypting a session key

The client asks the server to decrypt a session key.  The encrypted
session key should have all information needed to select the
appropriate secret key or to delegate it to a smartcard.

@example
  SETKEY <keyGrip>
@end example

Tell the server about the key to be used for decryption.  If this is
not used, @command{gpg-agent} may try to figure out the key by trying to
decrypt the message with each key available.

@example
  PKDECRYPT
@end example

The agent checks whether this command is allowed and then does an
INQUIRY to get the ciphertext the client should then send the cipher
text.

@example
    S: INQUIRE CIPHERTEXT
    C: D (xxxxxx
    C: D xxxx)
    C: END
@end example

Please note that the server may send status info lines while reading the
data lines from the client.  The data send is a SPKI like S-Exp with
this structure:

@example
     (enc-val
       (<algo>
         (<param_name1> <mpi>)
 	   ...
         (<param_namen> <mpi>)))
@end example

Where algo is a string with the name of the algorithm; see the libgcrypt
documentation for a list of valid algorithms.  The number and names of
the parameters depend on the algorithm.  The agent does return an error
if there is an inconsistency.

If the decryption was successful the decrypted data is returned by
means of "D" lines.

Here is an example session:

@example
   C: PKDECRYPT
   S: INQUIRE CIPHERTEXT
   C: D (enc-val elg (a 349324324)
   C: D    (b 3F444677CA)))
   C: END
   S: # session key follows
   S: D (value 1234567890ABCDEF0)
   S: OK descryption successful
@end example


@node Agent PKSIGN
@subsection Signing a Hash

The client ask the agent to sign a given hash value.  A default key
will be chosen if no key has been set.  To set a key a client first
uses:

@example
   SIGKEY <keyGrip>
@end example

This can be used multiple times to create multiple signature, the list
of keys is reset with the next PKSIGN command or a RESET.  The server
test whether the key is a valid key to sign something and responds with
okay.

@example
   SETHASH --hash=<name>|<algo> <hexstring>
@end example

The client can use this command to tell the server about the data <hexstring>
(which usually is a hash) to be signed. <algo> is the decimal encoded hash
algorithm number as used by Libgcrypt.  Either <algo> or --hash=<name>
must be given.  Valid names for <name> are:

@table @code
@item sha1
@item sha256
@item rmd160
@item md5
@item tls-md5sha1
@end table

@noindent
The actual signing is done using

@example
   PKSIGN <options>
@end example

Options are not yet defined, but my later be used to choose among
different algorithms.  The agent does then some checks, asks for the
passphrase and as a result the server returns the signature as an SPKI
like S-expression in "D" lines:

@example
     (sig-val
       (<algo>
         (<param_name1> <mpi>)
 	   ...
         (<param_namen> <mpi>)))
@end example


The operation is affected by the option

@example
   OPTION use-cache-for-signing=0|1
@end example

The default of @code{1} uses the cache.  Setting this option to @code{0}
will lead @command{gpg-agent} to ignore the passphrase cache.  Note, that there is
also a global command line option for @command{gpg-agent} to globally disable the
caching.


Here is an example session:

@example
   C: SIGKEY <keyGrip>
   S: OK key available
   C: SIGKEY <keyGrip>
   S: OK key available
   C: PKSIGN
   S: # I did ask the user whether he really wants to sign
   S: # I did ask the user for the passphrase
   S: INQUIRE HASHVAL
   C: D ABCDEF012345678901234
   C: END
   S: # signature follows
   S: D (sig-val rsa (s 45435453654612121212))
   S: OK
@end example


@node Agent GENKEY
@subsection Generating a Key

This is used to create a new keypair and store the secret key inside the
active PSE --- which is in most cases a Soft-PSE.  An not yet defined
option allows to choose the storage location.  To get the secret key out
of the PSE, a special export tool has to be used.

@example
   GENKEY
@end example

Invokes the key generation process and the server will then inquire
on the generation parameters, like:

@example
   S: INQUIRE KEYPARM
   C: D (genkey (rsa (nbits  1024)))
   C: END
@end example

The format of the key parameters which depends on the algorithm is of
the form:

@example
    (genkey
      (algo
        (parameter_name_1 ....)
          ....
        (parameter_name_n ....)))
@end example

If everything succeeds, the server returns the *public key* in a SPKI
like S-Expression like this:

@example
     (public-key
       (rsa
 	 (n <mpi>)
 	 (e <mpi>)))
@end example

Here is an example session:

@example
   C: GENKEY
   S: INQUIRE KEYPARM
   C: D (genkey (rsa (nbits  1024)))
   C: END
   S: D (public-key
   S: D   (rsa (n 326487324683264) (e 10001)))
   S  OK key created
@end example

@node Agent IMPORT
@subsection Importing a Secret Key

This operation is not yet supported by GpgAgent.  Specialized tools
are to be used for this.

There is no actual need because we can expect that secret keys
created by a 3rd party are stored on a smartcard.  If we have
generated the key ourself, we do not need to import it.

@node Agent EXPORT
@subsection Export a Secret Key

Not implemented.

Should be done by an extra tool.

@node Agent ISTRUSTED
@subsection Importing a Root Certificate

Actually we do not import a Root Cert but provide a way to validate
any piece of data by storing its Hash along with a description and
an identifier in the PSE.  Here is the interface description:

@example
    ISTRUSTED <fingerprint>
@end example

Check whether the OpenPGP primary key or the X.509 certificate with the
given fingerprint is an ultimately trusted key or a trusted Root CA
certificate.  The fingerprint should be given as a hexstring (without
any blanks or colons or whatever in between) and may be left padded with
00 in case of an MD5 fingerprint.  GPGAgent will answer with:

@example
    OK
@end example

The key is in the table of trusted keys.

@example
    ERR 304 (Not Trusted)
@end example

The key is not in this table.

Gpg needs the entire list of trusted keys to maintain the web of
trust; the following command is therefore quite helpful:

@example
    LISTTRUSTED
@end example

GpgAgent returns a list of trusted keys line by line:

@example
    S: D 000000001234454556565656677878AF2F1ECCFF P
    S: D 340387563485634856435645634856438576457A P
    S: D FEDC6532453745367FD83474357495743757435D S
    S: OK
@end example

The first item on a line is the hexified fingerprint where MD5
fingerprints are @code{00} padded to the left and the second item is a
flag to indicate the type of key (so that gpg is able to only take care
of PGP keys).  P = OpenPGP, S = S/MIME.  A client should ignore the rest
of the line, so that we can extend the format in the future.

Finally a client should be able to mark a key as trusted:

@example
   MARKTRUSTED @var{fingerprint} "P"|"S"
@end example

The server will then pop up a window to ask the user whether she
really trusts this key. For this it will probably ask for a text to
be displayed like this:

@example
   S: INQUIRE TRUSTDESC
   C: D Do you trust the key with the fingerprint @@FPR@@
   C: D bla fasel blurb.
   C: END
   S: OK
@end example

Known sequences with the pattern @@foo@@ are replaced according to this
table:

@table @code
@item @@FPR16@@
Format the fingerprint according to gpg rules for a v3 keys.
@item @@FPR20@@
Format the fingerprint according to gpg rules for a v4 keys.
@item @@FPR@@
Choose an appropriate format to format the fingerprint.
@item @@@@
Replaced by a single @code{@@}
@end table

@node Agent GET_PASSPHRASE
@subsection Ask for a passphrase

This function is usually used to ask for a passphrase to be used for
conventional encryption, but may also be used by programs which need
special handling of passphrases.  This command uses a syntax which helps
clients to use the agent with minimum effort.

@example
  GET_PASSPHRASE [--data] [--check] [--no-ask] [--repeat[=N]] [--qualitybar] @var{cache_id} [@var{error_message} @var{prompt} @var{description}]
@end example

@var{cache_id} is expected to be a string used to identify a cached
passphrase.  Use a @code{X} to bypass the cache.  With no other
arguments the agent returns a cached passphrase or an error.  By
convention either the hexified fingerprint of the key shall be used for
@var{cache_id} or an arbitrary string prefixed with the name of the
calling application and a colon: Like @code{gpg:somestring}.

@var{error_message} is either a single @code{X} for no error message or
a string to be shown as an error message like (e.g. "invalid
passphrase").  Blanks must be percent escaped or replaced by @code{+}'.

@var{prompt} is either a single @code{X} for a default prompt or the
text to be shown as the prompt.  Blanks must be percent escaped or
replaced by @code{+}.

@var{description} is a text shown above the entry field.  Blanks must be
percent escaped or replaced by @code{+}.

The agent either returns with an error or with a OK followed by the hex
encoded passphrase.  Note that the length of the strings is implicitly
limited by the maximum length of a command.  If the option
@option{--data} is used, the passphrase is not returned on the OK line
but by regular data lines; this is the preferred method.

If the option @option{--check} is used, the standard passphrase
constraints checks are applied.  A check is not done if the passphrase
has been found in the cache.

If the option @option{--no-ask} is used and the passphrase is not in the
cache the user will not be asked to enter a passphrase but the error
code @code{GPG_ERR_NO_DATA} is returned.

If the option @option{--qualitybar} is used and a minimum passphrase
length has been configured, a visual indication of the entered
passphrase quality is shown.

@example
  CLEAR_PASSPHRASE @var{cache_id}
@end example

may be used to invalidate the cache entry for a passphrase.  The
function returns with OK even when there is no cached passphrase.


@node Agent GET_CONFIRMATION
@subsection Ask for confirmation

This command may be used to ask for a simple confirmation by
presenting a text and 2 buttons: Okay and Cancel.

@example
  GET_CONFIRMATION @var{description}
@end example

@var{description}is displayed along with a Okay and Cancel
button. Blanks must be percent escaped or replaced by @code{+}.  A
@code{X} may be used to display confirmation dialog with a default
text.

The agent either returns with an error or with a OK.  Note, that the
length of @var{description} is implicitly limited by the maximum
length of a command.



@node Agent HAVEKEY
@subsection Check whether a key is available

This can be used to see whether a secret key is available.  It does
not return any information on whether the key is somehow protected.

@example
  HAVEKEY @var{keygrips}
@end example

The agent answers either with OK or @code{No_Secret_Key} (208).  The
caller may want to check for other error codes as well.  More than one
keygrip may be given.  In this case the command returns success if at
least one of the keygrips corresponds to an available secret key.


@node Agent LEARN
@subsection Register a smartcard

@example
  LEARN [--send]
@end example

This command is used to register a smartcard.  With the --send
option given the certificates are send back.


@node Agent PASSWD
@subsection Change a Passphrase

@example
  PASSWD @var{keygrip}
@end example

This command is used to interactively change the passphrase of the key
identified by the hex string @var{keygrip}.


@node Agent UPDATESTARTUPTTY
@subsection Change the standard display

@example
  UPDATESTARTUPTTY
@end example

Set the startup TTY and X-DISPLAY variables to the values of this
session.  This command is useful to direct future pinentry invocations
to another screen.  It is only required because there is no way in the
ssh-agent protocol to convey this information.


@node Agent GETEVENTCOUNTER
@subsection Get the Event Counters

@example
  GETEVENTCOUNTER
@end example

This function return one status line with the current values of the
event counters.  The event counters are useful to avoid polling by
delaying a poll until something has changed.  The values are decimal
numbers in the range @code{0} to @code{UINT_MAX} and wrapping around to
0.  The actual values should not be relied upon; they shall only be used
to detect a change.

The currently defined counters are are:
@table @code
@item ANY
Incremented with any change of any of the other counters.
@item KEY
Incremented for added or removed private keys.
@item CARD
Incremented for changes of the card readers stati.
@end table

@node Agent GETINFO
@subsection  Return information about the process

This is a multipurpose function to return a variety of information.

@example
GETINFO @var{what}
@end example

The value of @var{what} specifies the kind of information returned:
@table @code
@item version
Return the version of the program.
@item pid
Return the process id of the process.
@item socket_name
Return the name of the socket used to connect the agent.
@item ssh_socket_name
Return the name of the socket used for SSH connections.  If SSH support
has not been enabled the error @code{GPG_ERR_NO_DATA} will be returned.
@end table

@node Agent OPTION
@subsection Set options for the session

Here is a list of session options which are not yet described with
other commands.  The general syntax for an Assuan option is:

@smallexample
OPTION  @var{key}=@var{value}
@end smallexample

@noindent
Supported @var{key}s are:

@table @code
@item agent-awareness
This may be used to tell gpg-agent of which gpg-agent version the
client is aware of.  gpg-agent uses this information to enable
features which might break older clients.

@item putenv
Change the session's environment to be used for the
Pinentry.  Valid values are:

  @table @code
  @item @var{name}
  Delete envvar @var{name}
  @item @var{name}=
  Set envvar @var{name} to the empty string
  @item @var{name}=@var{value}
  Set envvar @var{name} to the string @var{value}.
  @end table

@item use-cache-for-signing
See Assuan command @code{PKSIGN}.

@item allow-pinentry-notify
This does not need any value.  It is used to enable the
PINENTRY_LAUNCHED inquiry.

@ifset gpgtwoone
@item pinentry-mode
This option is used to change the operation mode of the pinentry.  The
following values are defined:

  @table @code
  @item ask
  This is the default mode which pops up a pinentry as needed.

  @item cancel
  Instead of popping up a pinentry, return the error code
  @code{GPG_ERR_CANCELED}.

  @item error
  Instead of popping up a pinentry, return the error code
  @code{GPG_ERR_NO_PIN_ENTRY}.

  @item loopback
  Use a loopback pinentry.  This fakes a pinentry by using inquiries
  back to the caller to ask for a passphrase.  This option may only be
  set if the agent has been configured for that.
  Use the @xref{option --allow-loopback-pinentry}.

  @end table
@end ifset

@ifset gpgtwoone
@item cache-ttl-opt-preset
This option sets the cache TTL for new entries created by GENKEY and
PASSWD commands when using the @option{--preset} option.  It it is not
used a default value is used.
@end ifset

@ifset gpgtwoone
@item s2k-count
Instead of using the standard S2K count (which is computed on the
fly), the given S2K count is used for new keys or when changing the
passphrase of a key.  Values below 65536 are considered to be 0.  This
option is valid for the entire session or until reset to 0.  This
option is useful if the key is later used on boxes which are either
much slower or faster than the actual box.
@end ifset

@end table


@mansect see also
@ifset isman
@command{gpg2}(1),
@command{gpgsm}(1),
@command{gpg-connect-agent}(1),
@command{scdaemon}(1)
@end ifset
@include see-also-note.texi