Ubuntu Manpage: gpgsm - CMS encryption and signing tool

Provided by: gpgsm_2.2.4-1ubuntu1.6_amd64

NAME

       gpgsm - CMS encryption and signing tool

SYNOPSIS

       gpgsm [--homedir dir] [--options file] [options] command [args]

DESCRIPTION

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

COMMANDS

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

Commands not specific to the function

--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.

--warranty
Print warranty information. 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.

Commands to select the type of operation

--encrypt
Perform an encryption. The keys the data is encrypted to must be set using the
option --recipient.

--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.

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

--verify
Check a signature file for validity. Depending on the arguments a detached
signature may also be checked.

--server
Run in server mode and wait for commands on the stdin.

--call-dirmngr command [args]
Behave as a Dirmngr client issuing the request command with the optional list of
args. The output of the Dirmngr is printed stdout. Please note that file names
given as arguments should have an absolute file name (i.e. commencing with /)
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. 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 gpgsm. See the Dirmngr manual for details.

--call-protect-tool arguments
Certain maintenance operations are done by an external program call 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. arguments are passed
verbatim to this command; use '--help' to get a list of supported operations.

How to manage the certificates and keys

--generate-key
--gen-key
This command allows the creation of a certificate signing request or a self-signed
certificate. It is commonly used along with the --output option to save the
created CSR or certificate into a file. If used with the --batch a parameter file
is used to create the CSR or certificate and it is further possible to create non-
self-signed certificates.

--list-keys
-k 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.

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

--list-external-keys pattern
List certificates matching pattern using an external server. This utilizes the
dirmngr service.

--list-chain
Same as --list-keys but also prints all keys making up the chain.

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

--dump-chain
Same as --dump-keys but also prints all keys making up the chain.

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

--dump-external-keys pattern
List certificates matching pattern using an external server. This utilizes the
dirmngr service. It uses a format useful mainly for debugging.

--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 responder did accidentally revoke certificate. There is no
security issue with this command because gpgsm always make sure that the validity
of a certificate is checked right before it is used.

--delete-keys pattern
Delete the keys matching pattern. Note that there is no command to delete the
secret part of the key directly. In case you need to do this, you should run the
command gpgsm --dump-secret-keys KEYID before you delete the key, copy the string
of hex-digits in the ``keygrip'' line and delete the file consisting of these hex-
digits and the suffix .key from the ‘private-keys-v1.d’ directory below our GnuPG
home directory (usually ‘~/.gnupg’).

--export [pattern]
Export all certificates stored in the Keybox or those specified by the optional
pattern. Those pattern consist of a list of user ids (see: [how-to-specify-a-user-
id]). When used along with the --armor option a few informational lines are
prepended before each block. There is one limitation: As there is no commonly
agreed upon way to pack more than one certificate into an ASN.1 structure, the
binary export (i.e. without using armor) works only for the export of one
certificate. Thus it is required to specify a pattern which yields exactly one
certificate. Ephemeral certificate are only exported if all pattern are given as
fingerprints or keygrips.

--export-secret-key-p12 key-id
Export the private key and the certificate identified by key-id in a PKCS#12
format. When used with the --armor option a few informational lines are prepended
to the output. Note, that the PKCS#12 format is not very secure and this command
is only provided if there is no other way to exchange the private key. (See:
[option --p12-charset].)

--export-secret-key-p8 key-id
--export-secret-key-raw key-id
Export the private key of the certificate identified by key-id with any encryption
stripped. The ...-raw command exports in PKCS#1 format; the ...-p8 command exports
in PKCS#8 format. When used with the --armor option a few informational lines are
prepended to the output. These commands are useful to prepare a key for use on a
TLS server.

--import [files]
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.

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

--change-passphrase user_id
--passwd user_id
Change the passphrase of the private key belonging to the certificate specified as
user_id. Note, that changing the passphrase/PIN of a smartcard is not yet
supported.

OPTIONS

GPGSM features a bunch of options to control the exact behaviour and to change the default
configuration.

How to change the configuration

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

--options file
Reads configuration from file instead of from the default per-user configuration
file. The default configuration file is named ‘gpgsm.conf’ and expected in the
‘.gnupg’ directory directly below the home directory of the user.

--homedir dir
Set the name of the home directory to dir. If this option is not used, the home
directory defaults to ‘~/.gnupg’. It is only recognized when given on the command
line. It also overrides any home directory stated through the environment variable
‘GNUPGHOME’ or (on Windows systems) by means of the Registry entry
HKCU\Software\GNU\GnuPG:HomeDir.

On Windows systems it is possible to install GnuPG as a portable application. In
this case only this command line option is considered, all other ways to set a home
directory are ignored.

To install GnuPG as a portable application under Windows, create an empty file
named ‘gpgconf.ctl’ in the same directory as the tool ‘gpgconf.exe’. The root of
the installation is then that directory; or, if ‘gpgconf.exe’ has been installed
directly below a directory named ‘bin’, its parent directory. You also need to
make sure that the following directories exist and are writable: ‘ROOT/home’ for
the GnuPG home and ‘ROOT/var/cache/gnupg’ for internal cache files.

-v

--verbose
Outputs additional information while running. You can increase the verbosity by
giving several verbose commands to gpgsm, such as '-vv'.

--policy-file filename
Change the default name of the policy file to filename.

--agent-program file
Specify an agent program to be used for secret key operations. The default value
is determined by running the command gpgconf. Note that the pipe symbol (|) is
used for a regression test suite hack and may thus not be used in the file name.

--dirmngr-program file
Specify a dirmngr program to be used for CRL checks. The default value is
‘/usr/bin/dirmngr’.

--prefer-system-dirmngr
This option is obsolete and ignored.

--disable-dirmngr
Entirely disable the use of the Dirmngr.

--no-autostart
Do not start the gpg-agent or the dirmngr if it has not yet been started and its
service is required. This option is mostly useful on machines where the connection
to gpg-agent has been redirected to another machines. If dirmngr is required on
the remote machine, it may be started manually using gpgconf --launch dirmngr.

--no-secmem-warning
Do not print a warning when the so called "secure memory" cannot be used.

--log-file file
When running in server mode, append all logging output to file. Use ‘socket://’ to
log to socket.

Certificate related options

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

--enable-crl-checks
--disable-crl-checks
By default the 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.

--enable-trusted-cert-crl-check
--disable-trusted-cert-crl-check
By default the 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 will not 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 ‘trustlist.txt’

--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
intervals (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 --with-validation for a key listing command.
This option should not be used in a configuration file.

--enable-ocsp
--disable-ocsp
By default OCSP checks are disabled. The enable option may be used to enable OCSP
checks via Dirmngr. If CRL checks are also enabled, CRLs will be used as a
fallback if for some reason an OCSP request will not succeed. Note, that you have
to allow OCSP requests in Dirmngr's configuration too (option --allow-ocsp) and
configure Dirmngr properly. If you do not do so you will get the error code 'Not
supported'.

--auto-issuer-key-retrieve
If a required certificate is missing while validating the chain of certificates,
try to load that certificate from an external location. This usually means that
Dirmngr is employed to search for the certificate. Note that this option makes a
"web bug" like behavior possible. LDAP server operators can see which keys you
request, so by sending you a message signed by a brand new key (which you naturally
will not have on your local keybox), the operator can tell both your IP address and
the time when you verified the signature.

--validation-model name
This option changes the default validation model. The only possible values are
"shell" (which is the default), "chain" which forces the use of the chain model and
"steed" for a new simplified model. The chain model is also used if an option in
the ‘trustlist.txt’ or an attribute of the certificate requests it. However the
standard model (shell) is in that case always tried first.

--ignore-cert-extension oid
Add oid to the list of ignored certificate extensions. The oid is expected to be
in dotted decimal form, like 2.5.29.3. This option may be used more than once.
Critical flagged certificate extensions matching one of the OIDs in the list are
treated as if they are actually handled and thus the certificate will not be
rejected due to an unknown critical extension. Use this option with care because
extensions are usually flagged as critical for a reason.

Input and Output

--armor
-a Create PEM encoded output. Default is binary output.

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

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

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

--assume-binary
Assume the input data is binary encoded.

--p12-charset name
gpgsm uses the UTF-8 encoding when encoding passphrases for PKCS#12 files. This
option may be used to force the passphrase to be encoded in the specified encoding
name. This is useful if the application used to import the key uses a different
encoding and thus will not be able to import a file generated by gpgsm. Commonly
used values for name are Latin1 and CP850. Note that gpgsm itself automagically
imports any file with a passphrase encoded to the most commonly used encodings.

--default-key user_id
Use user_id as the standard key for signing. This key is used if no other key has
been defined as a signing key. Note, that the first --local-users option also sets
this key if it has not yet been set; however --default-key always overrides this.

--local-user user_id

-u user_id
Set the user(s) to be used for signing. The default is the first secret key found
in the database.

--recipient name
-r Encrypt to the user id name. There are several ways a user id may be given (see:
[how-to-specify-a-user-id]).

--output file
-o file
Write output to file. The default is to write it to stdout.

--with-key-data
Displays extra information with the --list-keys commands. Especially a line tagged
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. Implies --with-colons.

--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 certificate in the DB. This option is therefore useful to simply
verify a certificate.

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

--with-keygrip
Include the keygrip in standard key listings. Note that the keygrip is always
listed in --with-colons mode.

--with-secret
Include info about the presence of a secret key in public key listings done with
--with-colons.

How to change how the CMS is created

--include-certs n
Using 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 and all other
positive values include up to n certificates starting with the signer cert. The
default is -2.

--cipher-algo oid
Use the cipher algorithm with the ASN.1 object identifier oid for encryption. For
convenience the strings 3DES, AES and AES256 may be used instead of their OIDs.
The default is AES (2.16.840.1.101.3.4.1.2).

--digest-algo name
Use name as the message digest algorithm. Usually this algorithm is deduced from
the respective signing certificate. This option forces the use of the given
algorithm and may lead to severe interoperability problems.

Doing things one usually do not want to do

--extra-digest-algo name
Sometimes signatures are broken in that they announce a different digest algorithm
than actually used. gpgsm uses a one-pass data processing model and thus needs to
rely on the announced digest algorithms to properly hash the data. As a workaround
this option may be used to tell gpgsm to also hash the data using the algorithm
name; this slows processing down a little bit but allows verification of such
broken signatures. If gpgsm prints an error like ``digest algo 8 has not been
enabled'' you may want to try this option, with 'SHA256' for name.

--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. Alternatively
epoch may be given as a full ISO time string (e.g. "20070924T154812").

--with-ephemeral-keys
Include ephemeral flagged keys in the output of key listings. Note that they are
included anyway if the key specification for a listing is given as fingerprint or
keygrip.

--debug-level level
Select the debug level for investigating problems. level may be a numeric value or
by 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; using --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:

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

Note, that all flags set using this option may get overridden by --debug-level.

--debug-all
Same as --debug=0xffffffff

--debug-allow-core-dump
Usually 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.

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

--debug-ignore-expiration
This is actually not a debugging option but only useful as such. It lets gpgsm
ignore all notAfter dates, this is used by the regression tests.

--passphrase-fd n
Read the passphrase from file descriptor n. Only the first line will be read from
file descriptor n. If you use 0 for n, the passphrase will be read from STDIN. This
can only be used if only one passphrase is supplied.

Note that this passphrase is only used if the option --batch has also been given.

--pinentry-mode mode
Set the pinentry mode to mode. Allowed values for mode are:

default
Use the default of the agent, which is ask.

ask Force the use of the Pinentry.

cancel Emulate use of Pinentry's cancel button.

error Return a Pinentry error (``No Pinentry'').

loopback
Redirect Pinentry queries to the caller. Note that in contrast to Pinentry
the user is not prompted again if he enters a bad password.

--no-common-certs-import
Suppress the import of common certificates on keybox creation.

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

HOW TO SPECIFY A USER ID

There are different ways to specify a user ID to GnuPG. Some of them are only valid for
gpg others are only good for gpgsm. Here is the entire list of ways to specify a key:

By key Id.
This format is deduced from the length of the string and its content or 0x prefix.
The key Id of an X.509 certificate are the low 64 bits of its SHA-1 fingerprint.
The use of key Ids is just a shortcut, for all automated processing the fingerprint
should be used.

When using gpg an exclamation mark (!) may be appended to force using the specified
primary or secondary key and not to try and calculate which primary or secondary
key to use.

The last four lines of the example give the key ID in their long form as internally
used by the OpenPGP protocol. You can see the long key ID using the option --with-
colons.

234567C4
0F34E556E
01347A56A
0xAB123456

234AABBCC34567C4
0F323456784E56EAB
01AB3FED1347A5612
0x234AABBCC34567C4

By fingerprint.
This format is deduced from the length of the string and its content or the 0x
prefix. Note, that only the 20 byte version fingerprint is available with gpgsm
(i.e. the SHA-1 hash of the certificate).

When using gpg an exclamation mark (!) may be appended to force using the specified
primary or secondary key and not to try and calculate which primary or secondary
key to use.

The best way to specify a key Id is by using the fingerprint. This avoids any
ambiguities in case that there are duplicated key IDs.

1234343434343434C434343434343434
123434343434343C3434343434343734349A3434
0E12343434343434343434EAB3484343434343434
0xE12343434343434343434EAB3484343434343434

gpgsm also accepts colons between each pair of hexadecimal digits because this is the de-
facto standard on how to present X.509 fingerprints. gpg also allows the use of the space
separated SHA-1 fingerprint as printed by the key listing commands.

By exact match on OpenPGP user ID.
This is denoted by a leading equal sign. It does not make sense for X.509
certificates.

=Heinrich Heine <heinrichh@uni-duesseldorf.de>

By exact match on an email address.
This is indicated by enclosing the email address in the usual way with left and
right angles.

<heinrichh@uni-duesseldorf.de>

By partial match on an email address.
This is indicated by prefixing the search string with an @. This uses a substring
search but considers only the mail address (i.e. inside the angle brackets).

@heinrichh

By exact match on the subject's DN.
This is indicated by a leading slash, directly followed by the RFC-2253 encoded DN
of the subject. Note that you can't use the string printed by gpgsm --list-keys
because that one has been reordered and modified for better readability; use
--with-colons to print the raw (but standard escaped) RFC-2253 string.

/CN=Heinrich Heine,O=Poets,L=Paris,C=FR

By exact match on the issuer's DN.
This is indicated by a leading hash mark, directly followed by a slash and then
directly followed by the RFC-2253 encoded DN of the issuer. This should return the
Root cert of the issuer. See note above.

#/CN=Root Cert,O=Poets,L=Paris,C=FR

By exact match on serial number and issuer's DN.
This is indicated by a hash mark, followed by the hexadecimal representation of the
serial number, then followed by a slash and the RFC-2253 encoded DN of the issuer.
See note above.

#4F03/CN=Root Cert,O=Poets,L=Paris,C=FR

By keygrip.
This is indicated by an ampersand followed by the 40 hex digits of a keygrip.
gpgsm prints the keygrip when using the command --dump-cert. It does not yet work
for OpenPGP keys.

&D75F22C3F86E355877348498CDC92BD21010A480

By substring match.
This is the default mode but applications may want to explicitly indicate this by
putting the asterisk in front. Match is not case sensitive.

Heine
*Heine

. and + prefixes
These prefixes are reserved for looking up mails anchored at the end and for a word
search mode. They are not yet implemented and using them is undefined.

Please note that we have reused the hash mark identifier which was used in old
GnuPG versions to indicate the so called local-id. It is not anymore used and
there should be no conflict when used with X.509 stuff.

Using the RFC-2253 format of DNs has the drawback that it is not possible to map
them back to the original encoding, however we don't have to do this because our
key database stores this encoding as meta data.

EXAMPLES

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

FILES

There are a few configuration files to control certain aspects of gpgsm's operation.
Unless noted, they are expected in the current home directory (see: [option --homedir]).

gpgsm.conf
This is the standard configuration file read by 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 (see:
[gpgsm-option --options]). You should backup this file.

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. You
should backup this file.

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

# Allowed policies
2.289.9.9

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 whitespace, followed by exactly 40 hex characters, 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 the
certificate is trusted; in general the certificates listed in this file need to be
listed also in ‘trustlist.txt’.

This is a global file an installed in the data directory (e.g.
‘/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.

Every time 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.

help.txt
This is plain text file with a few help entries used with pinentry as well as a
large list of help items for gpg and gpgsm. The standard file has English help
texts; to install localized versions use filenames like ‘help.LL.txt’ with LL
denoting the locale. GnuPG comes with a set of predefined help files in the data
directory (e.g. ‘/usr/share/gnupg/gnupg/help.de.txt’) and allows overriding of any
help item by help files stored in the system configuration directory (e.g.
‘/etc/gnupg/help.de.txt’). For a reference of the help file's syntax, please see
the installed ‘help.txt’ file.

com-certs.pem
This file is a collection of common certificates used to populated a newly created
‘pubring.kbx’. An administrator may replace this file with a custom one. The
format is a concatenation of PEM encoded X.509 certificates. This global file is
installed in the data directory (e.g. ‘/usr/share/gnupg/com-certs.pem’).

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 a small helper script is provided to create these files (see:
[addgnupghome]).

For internal purposes gpgsm creates and maintains a few other files; they all live in the
current home directory (see: [option --homedir]). Only gpgsm may modify these files.

pubring.kbx
This a database file storing the certificates as well as meta information. For
debugging purposes the tool kbxutil may be used to show the internal structure of
this file. You should backup this file.

random_seed
This content of this file is used to maintain the internal state of the random
number generator across invocations. The same file is used by other programs of
this software too.

S.gpg-agent
If this file exists gpgsm will first try to connect to this socket for accessing
gpg-agent before starting a new gpg-agent instance. Under Windows this socket
(which in reality be a plain file describing a regular TCP listening port) is the
standard way of connecting the gpg-agent.