Invoking GPG-AGENT
******************

gpg-agent.1

synopsis

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).

See Option Index,for an index to GPG-AGENT's commands and options.

commands

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

Option Summary
==============

--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.

          [file opt-homedir.texi not included]

-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.  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.  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 emulation of 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:

          echo UPDATESTARTUPTTY | gpg-connect-agent

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

files

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 (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:

            # 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

     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 keygrip may be prefixed with a ! to disable an entry entry.

     The following example lists exactly one key.  Note that keys available through a OpenPGP smartcard in the active smartcard reader are implicitly added to this list; i.e. there is no need to list them.

            # Key added on 2005-02-25 15:08:29
            5A6592BF45DC73BD876874A28FD4639282E29B52 0

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

Use of some 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 and disable-scdaemon.  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.

examples

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).

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 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 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.

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.

       SETKEY <keyGrip>

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

       PKDECRYPT

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.

         S: INQUIRE CIPHERTEXT
         C: D (xxxxxx
         C: D xxxx)
         C: END

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:

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

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:

        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

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:

        SIGKEY <keyGrip>

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.

        SETHASH --hash=<name>|<algo> <hexstring>

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:

sha1

sha256

rmd160

md5

tls-md5sha1

The actual signing is done using

        PKSIGN <options>

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:

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

The operation is affected by the option

        OPTION use-cache-for-signing=0|1

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

Here is an example session:

        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

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.

        GENKEY

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

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

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

         (genkey
           (algo
             (parameter_name_1 ....)
               ....
             (parameter_name_n ....)))

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

          (public-key
            (rsa
      	 (n <mpi>)
      	 (e <mpi>)))

Here is an example session:

        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

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.

Export a Secret Key
-------------------

Not implemented.

Should be done by an extra tool.

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:

         ISTRUSTED <fingerprint>

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:

         OK

The key is in the table of trusted keys.

         ERR 304 (Not Trusted)

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:

         LISTTRUSTED

GpgAgent returns a list of trusted keys line by line:

         S: D 000000001234454556565656677878AF2F1ECCFF P
         S: D 340387563485634856435645634856438576457A P
         S: D FEDC6532453745367FD83474357495743757435D S
         S: OK

The first item on a line is the hexified fingerprint where MD5 fingerprints are 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:

        MARKTRUSTED FINGERPRINT "P"|"S"

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:

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

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

@FPR16@
     Format the fingerprint according to gpg rules for a v3 keys.

@FPR20@
     Format the fingerprint according to gpg rules for a v4 keys.

@FPR@
     Choose an appropriate format to format the fingerprint.

@@
     Replaced by a single @

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.

       GET_PASSPHRASE [--data] [--check] [--no-ask] [--repeat[=N]] [--qualitybar] CACHE_ID [ERROR_MESSAGE PROMPT DESCRIPTION]

CACHE_ID is expected to be a string used to identify a cached passphrase.  Use a 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 CACHE_ID or an arbitrary string prefixed with the name of the calling application and a colon: Like gpg:somestring.

ERROR_MESSAGE is either a single 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 +'.

PROMPT is either a single X for a default prompt or the text to be shown as the prompt.  Blanks must be percent escaped or replaced by +.

DESCRIPTION is a text shown above the entry field.  Blanks must be percent escaped or replaced by +.

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 --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 --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 --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 GPG_ERR_NO_DATA is returned.

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

       CLEAR_PASSPHRASE CACHE_ID

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

Ask for confirmation
--------------------

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

       GET_CONFIRMATION DESCRIPTION

DESCRIPTIONis displayed along with a Okay and Cancel button. Blanks must be percent escaped or replaced by +.  A 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 DESCRIPTION is implicitly limited by the maximum length of a command.

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.

       HAVEKEY KEYGRIPS

The agent answers either with OK or 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.

Register a smartcard
--------------------

       LEARN [--send]

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

Change a Passphrase
-------------------

       PASSWD KEYGRIP

This command is used to interactively change the passphrase of the key identified by the hex string KEYGRIP.

Change the standard display
---------------------------

       UPDATESTARTUPTTY

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.

Get the Event Counters
----------------------

       GETEVENTCOUNTER

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 0 to 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:

ANY
     Incremented with any change of any of the other counters.

KEY
     Incremented for added or removed private keys.

CARD
     Incremented for changes of the card readers stati.

Return information about the process
------------------------------------

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

     GETINFO WHAT

The value of WHAT specifies the kind of information returned:

version
     Return the version of the program.

pid
     Return the process id of the process.

socket_name
     Return the name of the socket used to connect the agent.

ssh_socket_name
     Return the name of the socket used for SSH connections.  If SSH support has not been enabled the error GPG_ERR_NO_DATA will be returned.

see also
     [file see-also-note.texi not included]