gnupg/doc/gpgsm.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.

@node Invoking GPGSM
@chapter Invoking GPGSM
@cindex GPGSM command options
@cindex command options
@cindex options, GPGSM command

@manpage gpgsm.1
@ifset manverb
.B gpgsm
\- CMS encryption and signing tool
@end ifset

@mansect synopsis
@ifset manverb
.B  gpgsm
.RB [ \-\-homedir
.IR dir ]
.RB [ \-\-options
.IR file ]
.RI [ options ]  
.I command
.RI [ args ]
@end ifset


@mansect description
@command{gpgsm} is a tool similar to @command{gpg} to provide digital
encryption and signing servicesd on X.509 certificates and the CMS
protocol.  It is mainly used as a backend for S/MIME mail processing.
@command{gpgsm} includes a full features certificate management and
complies with all rules defined for the German Sphinx project.

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

@menu
* GPGSM Commands::        List of all commands.
* GPGSM Options::         List of all options.
* GPGSM Configuration::   Configuration files.
* GPGSM Examples::        Some usage examples.

Developer information:
* Unattended Usage::      Using @command{gpgsm} from other programs.
* GPGSM Protocol::        The protocol the server mode uses.
@end menu

@c *******************************************
@c ***************            ****************
@c ***************  COMMANDS  ****************
@c ***************            ****************
@c *******************************************
@mansect commands
@node GPGSM Commands
@section Commands

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

@menu
* General GPGSM Commands::        Commands not specific to the functionality.
* Operational GPGSM Commands::    Commands to select the type of operation.
* Certificate Management::        How to manage certificates.
@end menu


@c *******************************************
@c **********  GENERAL COMMANDS  *************
@c *******************************************
@node General GPGSM Commands
@subsection Commands not specific to the function

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

@item --help, -h
@opindex help
Print a usage message summarizing the most usefule command-line options.
Not that you can abbreviate this command.

@item --warranty
@opindex warranty
Print warranty information.

@item --dump-options
@opindex dump-options
Print a list of all available options and commands.  Not that you can
abbreviate this command.
@end table


@c *******************************************
@c ********  OPERATIONAL COMMANDS  ***********
@c *******************************************
@node Operational GPGSM Commands
@subsection Commands to select the type of operation

@table @gnupgtabopt
@item --encrypt
@opindex encrypt
Perform an encryption.  The keys the data is encrypted too must be set
using the option @option{--recipient}.

@item --decrypt
@opindex decrypt
Perform a decryption; the type of input is automatically determined.  It
may either be in binary form or PEM encoded; automatic determination of
base-64 encoding is not done.

@item --sign
@opindex sign
Create a digital signature.  The key used is either the fist one found
in the keybox or those set with the @option{--local-user} option.

@item --verify
@opindex verify
Check a signature file for validity.  Depending on the arguments a
detached signatrue may also be checked.
 
@item --server
@opindex server
Run in server mode and wait for commands on the @code{stdin}.

@item --call-dirmngr @var{command} [@var{args}]
@opindex call-dirmngr
Behave as a Dirmngr client issuing the request @var{command} with the
optional list of @var{args}.  The output of the Dirmngr is printed
stdout.  Please note that file names given as arguments should have an
absulte file name (i.e. commencing with @code{/} because they are
passed verbatim to the Dirmngr and the working directory of the
Dirmngr might not be the same as the one of this client.  Currently it
is not possible to pass data via stdin to the Dirmngr.  @var{command}
should not contain spaces.

This is command is required for certain maintaining tasks of the dirmngr
where a dirmngr must be able to call back to @command{gpgsm}.  See the Dirmngr
manual for details.

@item --call-protect-tool @var{arguments}
@opindex call-protect-tool
Certain maintenance operations are done by an external program call
@command{gpg-protect-tool}; this is usually not installed in a directory
listed in the PATH variable.  This command provides a simple wrapper to
access this tool.  @var{arguments} are passed verbatim to this command;
use @samp{--help} to get a list of supported operations. 


@end table


@c *******************************************
@c *******  CERTIFICATE MANAGEMENT  **********
@c *******************************************
@node Certificate Management
@subsection How to manage the certificates and keys

@table @gnupgtabopt
@item --gen-key
@opindex gen-key
Generate a new key and a certificate request.

@item --list-keys
@itemx -k 
@opindex list-keys
List all available certificates stored in the local key database.
Note that the displayed data might be reformatted for better human
readability and illegal characters are replaced by safe substitutes.

@item --list-secret-keys
@itemx -K
@opindex list-secret-keys
List all available certificates for which a corresponding a secret key
is available.

@item --list-external-keys @var{pattern}
@opindex list-keys
List certificates matching @var{pattern} using an external server.  This
utilizes the @code{dirmngr} service.  

@item --list-chain
@opindex list-chain
Same as @option{--list-keys} but also prints all keys making up the chain.


@item --dump-cert
@itemx --dump-keys
@opindex dump-cert
@opindex dump-keys
List all available certificates stored in the local key database using a
format useful mainly for debugging.

@item --dump-chain
@opindex dump-chain
Same as @option{--dump-keys} but also prints all keys making up the chain.

@item --dump-secret-keys
@opindex dump-secret-keys
List all available certificates for which a corresponding a secret key
is available using a format useful mainly for debugging.

@item --dump-external-keys @var{pattern}
@opindex dump-external-keys
List certificates matching @var{pattern} using an external server.
This utilizes the @code{dirmngr} service.  It uses a format useful
mainly for debugging.

@item --keydb-clear-some-cert-flags
@opindex keydb-clear-some-cert-flags
This is a debugging aid to reset certain flags in the key database
which are used to cache certain certificate stati.  It is especially
useful if a bad CRL or a weird running OCSP reponder did accidently
revoke certificate.  There is no security issue with this command
because @command{gpgsm} always make sure that the validity of a certificate is
checked right before it is used.

@item --delete-keys @var{pattern}
@opindex delete-keys
Delete the keys matching @var{pattern}.

@item --export [@var{pattern}]
@opindex export
Export all certificates stored in the Keybox or those specified by the
optional @var{pattern}.  When using along with the @code{--armor} option
a few informational lines are prepended before each block.

@item --export-secret-key-p12 @var{key-id}
@opindex export
Export the private key and the certificate identified by @var{key-id}
in a PKCS#12 format. When using along with the @code{--armor} option
a few informational lines are prepended to the output.  Note, that the
PKCS#12 format is higly insecure and this command is only provided if
there is no other way to exchange the private key.

@item --import [@var{files}]
@opindex import
Import the certificates from the PEM or binary encoded files as well as
from signed-only messages.  This command may also be used to import a
secret key from a PKCS#12 file.

@item --learn-card
@opindex learn-card
Read information about the private keys from the smartcard and import
the certificates from there.  This command utilizes the @command{gpg-agent}
and in turn the @command{scdaemon}.

@item --passwd @var{user_id}
@opindex passwd
Change the passphrase of the private key belonging to the certificate
specified as @var{user_id}.  Note, that changing the passphrase/PIN of a
smartcard is not yet supported.

@end table


@c *******************************************
@c ***************            ****************
@c ***************  OPTIONS   ****************
@c ***************            ****************
@c *******************************************
@mansect options
@node GPGSM Options
@section Option Summary

@command{GPGSM} comes features a bunch ofoptions to control the exact behaviour
and to change the default configuration.

@menu 
* Configuration Options::   How to change the configuration.
* Certificate Options::     Certificate related options.
* Input and Output::        Input and Output.
* CMS Options::             How to change how the CMS is created.
* Esoteric Options::        Doing things one usually don't want to do.
@end menu


@c *******************************************
@c ********  CONFIGURATION OPTIONS  **********
@c *******************************************
@node Configuration Options
@subsection How to change the configuration

These options are used to change the configuraton and are usually found
in the option file.

@table @gnupgtabopt

@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{gpgsm.conf} and expected in the @file{.gnupg} directory directly
below the home directory of the user.

@include opt-homedir.texi


@item -v
@item --verbose
@opindex v
@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 --policy-file @var{filename}
@opindex policy-file
Change the default name of the policy file to @var{filename}.

@item --agent-program @var{file}
@opindex agent-program
Specify an agent program to be used for secret key operations.  The
default value is the @file{/usr/local/bin/gpg-agent}.  This is only used
as a fallback when the envrionment variable @code{GPG_AGENT_INFO} is not
set or a running agent can't be connected.
  
@item --dirmngr-program @var{file}
@opindex dirmnr-program
Specify a dirmngr program to be used for @acronym{CRL} checks.  The
default value is @file{/usr/sbin/dirmngr}.  This is only used as a
fallback when the environment variable @code{DIRMNGR_INFO} is not set or
a running dirmngr can't be connected.

@item --prefer-system-dirmngr
@opindex prefer-system-dirmngr
If a system wide @command{dirmngr} is running in daemon mode, first try
to connect to this one.  Fallback to a pipe based server if this does
not work.

@item --no-secmem-warning
@opindex no-secmem-warning
Don't print a warning when the so called "secure memory" can't be used.

@item --log-file @var{file}
@opindex log-file
When running in server mode, append all logging output to @var{file}.

@end table


@c *******************************************
@c ********  CERTIFICATE OPTIONS  ************
@c *******************************************
@node Certificate Options
@subsection Certificate related options

@table @gnupgtabopt

@item  --enable-policy-checks
@itemx --disable-policy-checks
@opindex enable-policy-checks
@opindex disable-policy-checks
By default policy checks are enabled.  These options may be used to
change it.

@item  --enable-crl-checks
@itemx --disable-crl-checks
@opindex enable-crl-checks
@opindex disable-crl-checks
By default the @acronym{CRL} checks are enabled and the DirMngr is used
to check for revoked certificates.  The disable option is most useful
with an off-line network connection to suppress this check.

@item  --enable-trusted-cert-crl-check
@itemx --disable-trusted-cert-crl-check
@opindex enable-trusted-cert-crl-check
@opindex disable-trusted-cert-crl-check
By default the @acronym{CRL} for trusted root certificates are checked
like for any other certificates.  This allows a CA to revoke its own
certificates voluntary without the need of putting all ever issued
certificates into a CRL.  The disable option may be used to switch this
extra check off.  Due to the caching done by the Dirmngr, there won't be
any noticeable performance gain.  Note, that this also disables possible
OCSP checks for trusted root certificates.  A more specific way of
disabling this check is by adding the ``relax'' keyword to the root CA
line of the @file{trustlist.txt}


@item --force-crl-refresh
@opindex force-crl-refresh
Tell the dirmngr to reload the CRL for each request.  For better
performance, the dirmngr will actually optimize this by suppressing
the loading for short time intervalls (e.g. 30 minutes). This option
is useful to make sure that a fresh CRL is available for certificates
hold in the keybox.  The suggested way of doing this is by using it
along with the option @option{--with-validation} for a key listing
command.  This option should not be used in a configuration file. 

@item  --enable-ocsp
@itemx --disable-ocsp
@opindex enable-ocsp
@opindex disable-ocsp
Be default @acronym{OCSP} checks are disabled.  The enable opton may
be used to enable OCSP checks via Dirmngr.  If @acronym{CRL} checks
are also enabled, CRLs will be used as a fallback if for some reason an
OCSP request won't succeed.  Note, that you have to allow OCSP
requests in Dirmngr's configuration too (option 
@option{--allow-ocsp} and configure dirmngr properly.  If you don't do
so you will get the error code @samp{Not supported}.

@end table

@c *******************************************
@c ***********  INPUT AND OUTPUT  ************
@c *******************************************
@node Input and Output
@subsection Input and Output

@table @gnupgtabopt
@item --armor
@itemx -a
@opindex armor
@opindex -a
Create PEM encoded output.  Default is binary output. 

@item --base64 
@opindex base64
Create Base-64 encoded output; i.e. PEM without the header lines.

@item --assume-armor
@opindex assume-armor
Assume the input data is PEM encoded.  Default is to autodetect the
encoding but this is may fail.

@item --assume-base64
@opindex assume-base64
Assume the input data is plain base-64 encoded.

@item --assume-binary
@opindex assume-binary
Assume the input data is binary encoded.

@item --local-user @var{user_id}
@item -u @var{user_id}
@opindex local-user
@opindex -u
Set the user(s) to be used for signing.  The default is the first
secret key found in the database.


@item --recipient @var{name}
@itemx -r
@opindex recipient
Encrypt to the user id @var{name}.  There are several ways a user id
may be given (@pxref{how-to-specify-a-user-id}).


@item --output @var{file}
@itemx -o @var{file}
@opindex output
Write output to @var{file}.  The default is to write it to stdout.


@item --with-key-data
@opindex with-key-data
Displays extra information with the @code{--list-keys} commands.  Especially
a line tagged @code{grp} is printed which tells you the keygrip of a
key.  This string is for example used as the file name of the
secret key.

@item --with-validation
@opindex with-validation
When doing a key listing, do a full validation check for each key and
print the result.  This is usually a slow operation because it
requires a CRL lookup and other operations. 

When used along with --import, a validation of the certificate to
import is done and only imported if it succeeds the test.  Note that
this does not affect an already available cwertificate in the DB.
This option is therefore useful to simply verify a certificate.


@item --with-md5-fingerprint
For standard key listings, also print the MD5 fingerprint of the
certificate.

@end table

@c *******************************************
@c *************  CMS OPTIONS  ***************
@c *******************************************
@node CMS Options
@subsection How to change how the CMS is created.

@table @gnupgtabopt
@item --include-certs @var{n}
Using @var{n} of -2 includes all certificate except for the root cert,
-1 includes all certs, 0 does not include any certs, 1 includes only
the signers cert (this is the default) and all other positive
values include up to @var{n} certificates starting with the signer cert.
  
@end table



@c *******************************************
@c ********  ESOTERIC OPTIONS  ***************
@c *******************************************
@node Esoteric Options
@subsection Doing things one usually don't want to do.


@table @gnupgtabopt

@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 --with-ephemeral-keys
@opindex with-ephemeral-keys
Include ephemeral flagged keys in the output of key listings.

@item --debug-level @var{level}
@opindex debug-level
Select the debug level for investigating problems. @var{level} may be
one of:

@table @code
@item none
no debugging at all.
@item basic  
some basic debug messages
@item advanced
more verbose debug messages
@item expert
even more detailed messages
@item guru
all of the debug messages you can get
@end table

How these messages are mapped to the actual debugging flags is not
specified and may change with newer releaes 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; using @code{--debug-levels} is the
preferred method to select the debug verbosity.  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
@end table

Note, that all flags set using this option may get overriden by
@code{--debug-level}.

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

@item --debug-allow-core-dump
@opindex debug-allow-core-dump
Usually @command{gpgsm} tries to avoid dumping core by well written code and by
disabling core dumps for security reasons.  However, bugs are pretty
durable beasts and to squash them it is sometimes useful to have a core
dump.  This option enables core dumps unless the Bad Thing happened
before the option parsing.

@item --debug-no-chain-validation
@opindex debug-no-chain-validation
This is actually not a debugging option but only useful as such.  It
lets @command{gpgsm} bypass all certificate chain validation checks.

@item --debug-ignore-expiration
@opindex debug-ignore-expiration
This is actually not a debugging option but only useful as such.  It
lets @command{gpgsm} ignore all notAfter dates, this is used by the regresssion
tests.

@item --fixed-passphrase @var{string}
@opindex fixed-passphrase
Supply the passphrase @var{string} to the gpg-protect-tool.  This
option is only useful for the regression tests included with this
package and may be revised or removed at any time without notice.

@end table

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

@c *******************************************
@c ***************            ****************
@c ***************  USER ID   ****************
@c ***************            ****************
@c *******************************************
@mansect how to specify a user id
@ifset isman
@include specify-user-id.texi
@end ifset

@c *******************************************
@c ***************            ****************
@c ***************   FILES    ****************
@c ***************            ****************
@c *******************************************
@mansect files
@node GPGSM Configuration
@section Configuration files

There are a few configuration files to control certain aspects of
@command{gpgsm}'s operation. Unless noted, they are expected in the
current home directory (@pxref{option --homedir}).

@table @file

@item gpgsm.conf
@cindex gpgsm.conf
This is the standard configuration file read by @command{gpgsm} 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 default
name may be changed on the command line (@pxref{option
  --options}).

@item policies.txt
@cindex policies.txt
This is a list of allowed CA policies.  This file should list the
object identifiers of the policies line by line.  Empty lines and
lines starting with a hash mark are ignored.  Policies missing in this
file and not marked as critical in the certificate will print only a
warning; certificates with policies marked as critical and not listed
in this file will fail the signature verification.

For example, to allow only the policy 2.289.9.9, the file should look
like this:

@c man:.RS
@example
# Allowed policies
2.289.9.9  
@end example
@c man:.RE

@item qualified.txt
@cindex qualified.txt
This is the list of root certificates used for qualified certificates.
They are defined as certificates capable of creating legally binding
signatures in the same way as handwritten signatures are.  Comments
start with a hash mark and empty lines are ignored.  Lines do have a
length limit but this is not a serious limitation as the format of the
entries is fixed and checked by gpgsm: A non-comment line starts with
optional white spaces, followed by exactly 40 hex character, white space
and a lowercased 2 letter country code.  Additional data delimited with
by a white space is current ignored but might late be used for other
purposes.

Note that even if a certificate is listed in this file, this does not
mean that thecertificate is trusted; in general the certificates listed
in this file need to be listed also in @file{trustlist.txt}.

This is a global file an installed in the data directory
(e.g. @file{/usr/share/gnupg/qualified.txt}).  GnuPG installs a suitable
file with root certificates as used in Germany.  As new Root-CA
certificates may be issued over time, these entries may need to be
updated; new distributions of this software should come with an updated
list but it is still the responsibility of the Administrator to check
that this list is correct.

Everytime @command{gpgsm} uses a certificate for signing or verification
this file will be consulted to check whether the certificate under
question has ultimately been issued by one of these CAs.  If this is the
case the user will be informed that the verified signature represents a
legally binding (``qualified'') signature.  When creating a signature
using such a certificate an extra prompt will be issued to let the user
confirm that such a legally binding signature shall really be created.

Because this software has not yet been approved for use with such
certificates, appropriate notices will be shown to indicate this fact.

@end table

@c man:.RE
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}).

For internal purposes gpgsm creates and maintaines a few other files;
They all live in in the current home directory (@pxref{option
--homedir}).  Only @command{gpgsm} may modify these files.


@table @file
@item pubring.kbx
@cindex pubring.kbx
This a database file storing the certificates as well as meta
information.  For debugging purposes the tool @command{kbxutil} may be
used to show the internal structure of this file.
      
@item random_seed
@cindex random_seed
This content of this file is used to maintain the internal state of the
random number generator accross invocations.  The same file is used by
other programs of this software too.

@end table


@c *******************************************
@c ***************            ****************
@c ***************  EXAMPLES  ****************
@c ***************            ****************
@c *******************************************
@mansect examples
@node GPGSM Examples
@section Examples

@example
$ gpgsm -er goo@@bar.net <plaintext >ciphertext
@end example


@c man end


@c *******************************************
@c ***************              **************
@c ***************  UNATTENDED  **************
@c ***************              **************
@c *******************************************
@node Unattended Usage
@section Unattended Usage

@command{gpgsm} is often used as a backend engine by other software.  To help
with this a machine interface has been defined to have an unambiguous
way to do this.  This is most likely used with the @code{--server} command
but may also be used in the standard operation mode by using the
@code{--status-fd} option.

@menu
* Automated signature checking::  Automated signature checking.
@end menu

@node Automated signature checking,,,Unattended Usage
@section Automated signature checking

It is very important to understand the semantics used with signature
verification.  Checking a signature is not as simple as it may sound and
so the ooperation si a bit complicated.  In mosted cases it is required
to look at several status lines.  Here is a table of all cases a signed
message may have:

@table @asis
@item The signature is valid
This does mean that the signature has been successfully verified, the
certificates are all sane.  However there are two subcases with
important information:  One of the certificates may have expired or a
signature of a message itself as expired.  It is a sound practise to
consider such a signature still as valid but additional information
should be displayed.  Depending on the subcase @command{gpgsm} will issue
these status codes:
  @table @asis 
  @item signature valid and nothing did expire
  @code{GOODSIG}, @code{VALIDSIG}, @code{TRUST_FULLY}
  @item signature valid but at least one certificate has expired
  @code{EXPKEYSIG}, @code{VALIDSIG}, @code{TRUST_FULLY}
  @item signature valid but expired
  @code{EXPSIG}, @code{VALIDSIG}, @code{TRUST_FULLY}
  Note, that this case is currently not implemented.
  @end table

@item The signature is invalid
This means that the signature verification failed (this is an indication
of af a transfer error, a programm error or tampering with the message).
@command{gpgsm} issues one of these status codes sequences:
  @table @code
  @item  @code{BADSIG}
  @item  @code{GOODSIG}, @code{VALIDSIG} @code{TRUST_NEVER}
  @end table

@item Error verifying a signature
For some reason the signature could not be verified, i.e. it can't be
decided whether the signature is valid or invalid.  A common reason for
this is a missing certificate.

@end table


@c *******************************************
@c ***************           *****************
@c ***************  ASSSUAN  *****************
@c ***************           *****************
@c *******************************************
@manpause
@node GPGSM Protocol
@section The Protocol the Server Mode Uses.

Description of the protocol used to access @command{GPGSM}.
@command{GPGSM} does implement the Assuan protocol and in addition
provides a regular command line interface which exhibits a full client
to this protocol (but uses internal linking).  To start
@command{gpgsm} as a server the command line the option
@code{--server} must be used.  Additional options are provided to
select the communication method (i.e. the name of the socket).

We assume that the connection has already been established; see the
Assuan manual for details.

@menu
* GPGSM ENCRYPT::         Encrypting a message.
* GPGSM DECRYPT::         Decrypting a message.
* GPGSM SIGN::            Signing a message.
* GPGSM VERIFY::          Verifying a message.
* GPGSM GENKEY::          Generating a key.
* GPGSM LISTKEYS::        List available keys.
* GPGSM EXPORT::          Export certificates.
* GPGSM IMPORT::          Import certificates.
* GPGSM DELETE::          Delete certificates.
@end menu


@node GPGSM ENCRYPT
@subsection Encrypting a Message

Before encrytion can be done the recipient must be set using the
command:

@example
  RECIPIENT @var{userID}
@end example

Set the recipient for the encryption.  @var{userID} should be the
internal representation of the key; the server may accept any other way
of specification.  If this is a valid and trusted recipient the server
does respond with OK, otherwise the return is an ERR with the reason why
the recipient can't be used, the encryption will then not be done for
this recipient.  If the policy is not to encrypt at all if not all
recipients are valid, the client has to take care of this.  All
@code{RECIPIENT} commands are cumulative until a @code{RESET} or an
successful @code{ENCRYPT} command.

@example
  INPUT FD[=@var{n}] [--armor|--base64|--binary]
@end example

Set the file descriptor for the message to be encrypted to @var{n}.
Obviously the pipe must be open at that point, the server establishes
its own end.  If the server returns an error the client should consider
this session failed.  If @var{n} is not given, this commands uses the
last file descriptor passed to the application.
@xref{fun-assuan_sendfd, ,the assuan_sendfd function,assuan,the Libassuan
manual}, on how to do descriptor passing.

The @code{--armor} option may be used to advice the server that the
input data is in @acronym{PEM} format, @code{--base64} advices that a
raw base-64 encoding is used, @code{--binary} advices of raw binary
input (@acronym{BER}).  If none of these options is used, the server
tries to figure out the used encoding, but this may not always be
correct.

@example
  OUTPUT FD[=@var{n}] [--armor|--base64]
@end example

Set the file descriptor to be used for the output (i.e. the encrypted
message). Obviously the pipe must be open at that point, the server
establishes its own end.  If the server returns an error he client
should consider this session failed.

The option armor encodes the output in @acronym{PEM} format, the
@code{--base64} option applies just a base 64 encoding.  No option
creates binary output (@acronym{BER}).
  
The actual encryption is done using the command

@example
  ENCRYPT 
@end example

It takes the plaintext from the @code{INPUT} command, writes to the
ciphertext to the file descriptor set with the @code{OUTPUT} command,
take the recipients from all the recipients set so far.  If this command
fails the clients should try to delete all output currently done or
otherwise mark it as invalid.  @command{GPGSM} does ensure that there won't be any
security problem with leftover data on the output in this case.

This command should in general not fail, as all necessary checks have
been done while setting the recipients.  The input and output pipes are
closed.


@node GPGSM DECRYPT
@subsection Decrypting a message

Input and output FDs are set the same way as in encryption, but
@code{INPUT} refers to the ciphertext and output to the plaintext. There
is no need to set recipients.  @command{GPGSM} automatically strips any
@acronym{S/MIME} headers from the input, so it is valid to pass an
entire MIME part to the INPUT pipe.

The encryption is done by using the command

@example
  DECRYPT
@end example

It performs the decrypt operation after doing some check on the internal
state. (e.g. that all needed data has been set).  Because it utilizes
the GPG-Agent for the session key decryption, there is no need to ask
the client for a protecting passphrase - GpgAgent takes care of this by
requesting this from the user.


@node GPGSM SIGN
@subsection Signing a Message

Signing is usually done with these commands:

@example
  INPUT FD[=@var{n}] [--armor|--base64|--binary]
@end example

This tells @command{GPGSM} to read the data to sign from file descriptor @var{n}.

@example
  OUTPUT FD[=@var{m}] [--armor|--base64]
@end example

Write the output to file descriptor @var{m}.  If a detached signature is
requested, only the signature is written.

@example
  SIGN [--detached] 
@end example

Sign the data set with the INPUT command and write it to the sink set by
OUTPUT.  With @code{--detached}, a detached signature is created
(surprise).

The key used for signining is the default one or the one specified in
the configuration file.  To get finer control over the keys, it is
possible to use the command

@example
  SIGNER @var{userID}
@end example

to the signer's key.  @var{userID} should be the
internal representation of the key; the server may accept any other way
of specification.  If this is a valid and trusted recipient the server
does respond with OK, otherwise the return is an ERR with the reason why
the key can't be used, the signature will then not be created using
this key.  If the policy is not to sign at all if not all
keys are valid, the client has to take care of this.  All
@code{SIGNER} commands are cumulative until a @code{RESET} is done.
Note that a @code{SIGN} does not reset this list of signers which is in
contrats to the @code{RECIPIENT} command.


@node GPGSM VERIFY
@subsection Verifying a Message

To verify a mesage the command:

@example
  VERIFY
@end example

is used. It does a verify operation on the message send to the input FD.
The result is written out using status lines.  If an output FD was
given, the signed text will be written to that.  If the signature is a
detached one, the server will inquire about the signed material and the
client must provide it.

@node GPGSM GENKEY
@subsection Generating a Key

This is used to generate a new keypair, store the secret part in the
@acronym{PSE} and the public key in the key database.  We will probably
add optional commands to allow the client to select whether a hardware
token is used to store the key.  Configuration options to
@command{GPGSM} can be used to restrict the use of this command.

@example
  GENKEY 
@end example

@command{GPGSM} checks whether this command is allowed and then does an
INQUIRY to get the key parameters, the client should then send the
key parameters in the native format:

@example
    S: INQUIRE KEY_PARAM native
    C: D foo:fgfgfg
    C: D bar
    C: END
@end example    

Please note that the server may send Status info lines while reading the
data lines from the client.  After this the key generation takes place
and the server eventually does send an ERR or OK response.  Status lines
may be issued as a progress indicator.


@node GPGSM LISTKEYS
@subsection List available keys

To list the keys in the internal database or using an external key
provider, the command:

@example
  LISTKEYS  @var{pattern}
@end example

is used.  To allow multiple patterns (which are ORed during the search)
quoting is required: Spaces are to be translated into "+" or into "%20";
in turn this requires that the usual escape quoting rules are done.

@example
  LISTSECRETKEYS @var{pattern}
@end example

Lists only the keys where a secret key is available.

The list commands  commands are affected by the option

@example
  OPTION list-mode=@var{mode}
@end example

where mode may be:
@table @code
@item 0 
Use default (which is usually the same as 1).
@item 1
List only the internal keys.
@item 2
List only the external keys.
@item 3
List internal and external keys.
@end table

Note that options are valid for the entire session.
    

@node GPGSM EXPORT
@subsection Export certificates

To export certificate from the internal key database the command:

@example
  EXPORT @var{pattern}
@end example

is used.  To allow multiple patterns (which are ORed) quoting is
required: Spaces are to be translated into "+" or into "%20"; in turn
this requires that the usual escape quoting rules are done.

The format of the output depends on what was set with the OUTPUT
command.  When using @acronym{PEM} encoding a few informational lines
are prepended.


@node GPGSM IMPORT
@subsection Import certificates

To import certificates into the internal key database, the command

@example
  IMPORT
@end example

is used.  The data is expected on the file descriptor set with the
@code{INPUT} command.  Certain checks are performend on the
certificate.  Note that the code will also handle PKCS\#12 files and
import private keys; a helper program is used for that.


@node GPGSM DELETE
@subsection Delete certificates

To delete certificate the command

@example
  DELKEYS @var{pattern}
@end example

is used.  To allow multiple patterns (which are ORed) quoting is
required: Spaces are to be translated into "+" or into "%20"; in turn
this requires that the usual escape quoting rules are done.

The certificates must be specified unambiguously otherwise an error is
returned.


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