@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 or has been set using @command{gpg-preset-passphrase}. 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 or has been set using @command{gpg-preset-passphrase}. 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. @ifset gpgtwoone @item --disable-check-own-socket @opindex disable-check-own-socket @command{gpg-agent} employs a periodic self-test to detect a stolen socket. This usually means a second instance of @command{gpg-agent} has taken over the socket and @command{gpg-agent} will then terminate itself. This option may be used to disable this self-test for debugging purposes. @end ifset @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: @cartouche @smallexample # 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 smallexample @end cartouche 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. @cartouche @smallexample # 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 smallexample @end cartouche @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}, @code{disable-scdaemon}, and @code{disable-check-own-socket}. @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. @ifset gpgtwoone The @command{gpg-agent} may send status messages during a command or when returning from a command to inform a client about the progress or result of an operation. For example, the @var{INQUIRE_MAXLEN} status message may be sent during a server inquire to inform the client of the maximum usable length of the inquired data (which should not be exceeded). @end ifset @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 CLEAR_PASSPHRASE:: Expire a cached passphrase @ifset gpgtwoone * Agent PRESET_PASSPHRASE:: Set a passphrase for a keygrip @end ifset * 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 @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 ( ( ) ... ( ))) @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: @cartouche @smallexample C: PKDECRYPT S: INQUIRE CIPHERTEXT C: D (enc-val elg (a 349324324) C: D (b 3F444677CA))) C: END S: # session key follows S: S PADDING 0 S: D (value 1234567890ABCDEF0) S: OK descryption successful @end smallexample @end cartouche The “PADDING” status line is only send if gpg-agent can tell what kind of padding is used. As of now only the value 0 is used to indicate that the padding has been removed. @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 @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=| @end example The client can use this command to tell the server about the data (which usually is a hash) to be signed. is the decimal encoded hash algorithm number as used by Libgcrypt. Either or --hash= must be given. Valid names for are: @table @code @item sha1 The SHA-1 hash algorithm @item sha256 The SHA-256 hash algorithm @item rmd160 The RIPE-MD160 hash algorithm @item md5 The old and broken MD5 hash algorithm @item tls-md5sha1 A combined hash algorithm as used by the TLS protocol. @end table @noindent The actual signing is done using @example PKSIGN @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 ( ( ) ... ( ))) @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: @cartouche @smallexample C: SIGKEY S: OK key available C: SIGKEY 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 smallexample @end cartouche @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 @ifset gpgtwoone GENKEY [--no-protection] [--preset] [] @end ifset @ifclear gpgtwoone GENKEY @end ifclear @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 ) (e ))) @end example Here is an example session: @cartouche @smallexample 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 smallexample @end cartouche @ifset gpgtwoone The @option{--no-protection} option may be used to prevent prompting for a passphrase to protect the secret key while leaving the secret key unprotected. The @option{--preset} option may be used to add the passphrase to the cache using the default cache parameters. @end ifset @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 @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 CLEAR_PASSPHRASE @subsection Remove a cached passphrase Use this command to remove a cached passphrase. @example @ifset gpgtwoone CLEAR_PASSPHRASE [--mode=normal] @end ifset @ifclear gpgtwoone CLEAR_PASSPHRASE @end ifclear @end example @ifset gpgtwoone The @option{--mode=normal} option can be used to clear a @var{cache_id} that was set by gpg-agent. @end ifset @ifset gpgtwoone @node Agent PRESET_PASSPHRASE @subsection Set a passphrase for a keygrip This command adds a passphrase to the cache for the specified @var{keygrip}. @example PRESET_PASSPHRASE [--inquire] [] @end example The passphrase is a hexidecimal string when specified. When not specified, the passphrase will be retrieved from the pinentry module unless the @option{--inquire} option was specified in which case the passphrase will be retrieved from the client. The @var{timeout} parameter keeps the passphrase cached for the specified number of seconds. A value of @code{-1} means infinate while @code{0} means the default (currently only a timeout of -1 is allowed, which means to never expire it). @end ifset @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 @ifset gpgtwoone PASSWD [--cache-nonce=] [--passwd-nonce=] [--preset] @var{keygrip} @end ifset @ifclear gpgtwoone PASSWD @var{keygrip} @end ifclear @end example This command is used to interactively change the passphrase of the key identified by the hex string @var{keygrip}. @ifset gpgtwoone The @option{--preset} option may be used to add the new passphrase to the cache using the default cache parameters. @end ifset @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