gnupg/doc/gpg.texi

\input texinfo
@c This Texinfo document has been automatically generated by
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@setfilename gpg.info
@dircategory GnuPG
@direntry
* gpg: (gpg).                         GnuPG encryption and signing tool.
@end direntry

@node top
@top gpg
@menu
@end menu

@majorheading Name
gpg ---- encryption and signing tool

@majorheading Synopsis

@majorheading DESCRIPTION
@code{gpg} is the main program for the GnuPG system.

This man page only lists the commands and options available.
For more verbose documentation get the GNU Privacy Handbook (GPH) or
one of the other documents at http://www.gnupg.org/docs.html .

Please remember that option parsing stops as soon as a non option is
encountered, you can explicitly stop option parsing by using the
special option "---".

@majorheading COMMANDS
@code{gpg} recognizes these commands:

@table @asis
@item -s, ---sign
Make a signature. This command may be combined
with ---encrypt.

@item ---clearsign
Make a clear text signature.

@item -b, ---detach-sign
Make a detached signature.

@item -e, ---encrypt
Encrypt data. This option may be combined with ---sign.

@item -c, ---symmetric
Encrypt with symmetric cipher only.
This command asks for a passphrase.

@item ---store
Store only (make a simple RFC1991 packet).

@item ---decrypt @code{file}
Decrypt @code{file} (or stdin if no file is specified) and
write it to stdout (or the file specified with
---output). If the decrypted file is signed, the
signature is also verified. This command differs
from the default operation, as it never writes to the
filename which is included in the file and it
rejects files which don't begin with an encrypted
message.

@item ---verify @code{sigfile} @code{signed-files}
Assume that @code{sigfile} is a signature and verify it
without generating any output. With no arguments,
the signature packet is read from stdin. If
only a sigfile is given, it may be a complete
signature or a detached signature, in which case
the signed stuff is expected in a file without the
".sig" or ".asc" extension. 
With more than
1 argument, the first should be a detached signature
and the remaining files are the signed stuff. To read the signed
stuff from stdin, use @samp{-} as the second filename.
For security reasons a detached signature cannot read the signed
material from stdin without denoting it in the above way.

@item ---verify-files @code{files}
This is a special version of the ---verify command which does not work with
detached signatures. The command expects the files to be verified either
on the command line or reads the filenames from stdin; each name must be on
separate line. The command is intended for quick checking of many files.

@item ---encrypt-files @code{files}
This is a special version of the ---encrypt command. The command expects
the files to be encrypted either on the command line or reads the filenames
from stdin; each name must be on separate line. The command is intended
for a quick encryption of multiple files.

@item ---decrypt-files @code{files}
The same as ---encrypt-files with the difference that files will be
decrypted. The syntax or the filenames is the same.

@item ---list-keys @code{names}
@itemx ---list-public-keys @code{names}
List all keys from the public keyrings, or just the
ones given on the command line.

@item ---list-secret-keys @code{names}
List all keys from the secret keyrings, or just the ones given on the
command line. A '#' after the letters 'sec' means that the secret key
is not usable (for example, if it was created via
---export-secret-subkeys).

@item ---list-sigs @code{names}
Same as ---list-keys, but the signatures are listed too.

@item ---check-sigs @code{names}
Same as ---list-sigs, but the signatures are verified.

@item ---fingerprint @code{names}
List all keys with their fingerprints. This is the
same output as ---list-keys but with the additional output
of a line with the fingerprint. May also be combined
with ---list-sigs or --check-sigs.
If this command is given twice, the fingerprints of all
secondary keys are listed too.

@item ---list-packets
List only the sequence of packets. This is mainly
useful for debugging.

@item ---gen-key
Generate a new key pair. This command is normally only used
interactively.

There is an experimental feature which allows you to create keys
in batch mode. See the file @file{doc/DETAILS}
in the source distribution on how to use this.

@item ---edit-key @code{name}
Present a menu which enables you to do all key
related tasks:

@table @asis
@item sign
Make a signature on key of user @code{name}
If the key is not yet signed by the default
user (or the users given with -u), the
program displays the information of the key
again, together with its fingerprint and
asks whether it should be signed. This
question is repeated for all users specified
with -u.

@item lsign
Same as ---sign but the signature is marked as
non-exportable and will therefore never be used
by others. This may be used to make keys valid
only in the local environment.

@item nrsign
Same as ---sign but the signature is marked as non-revocable and can
therefore never be revoked.

@item nrlsign
Combines the functionality of nrsign and lsign to make a signature
that is both non-revocable and
non-exportable.

@item revsig
Revoke a signature. For every signature which has been generated by
one of the secret keys, GnuPG asks whether a revocation certificate
should be generated.

@item trust
Change the owner trust value. This updates the
trust-db immediately and no save is required.

@item disable
@itemx enable
Disable or enable an entire key. A disabled key can normally not be used
for encryption.

@item adduid
Create an alternate user id.

@item addphoto
Create a photographic user id.

@item deluid
Delete a user id.

@item addkey
Add a subkey to this key.

@item delkey
Remove a subkey.

@item addrevoker
Add a designated revoker. This takes one optional argument:
"sensitive". If a designated revoker is marked as sensitive, it will
not be exported by default (see
export-options).

@item revkey
Revoke a subkey.

@item expire
Change the key expiration time. If a subkey is selected, the
expiration time of this subkey will be changed. With no selection,
the key expiration of the primary key is changed.

@item passwd
Change the passphrase of the secret key.

@item primary
Flag the current user id as the primary one, removes the primary user
id flag from all other user ids and sets the timestamp of all affected
self-signatures one second ahead. Note that setting a photo user ID
as primary makes it primary over other photo user IDs, and setting a
regular user ID as primary makes it primary over other regular user
IDs.

@item uid @code{n}
Toggle selection of user id with index @code{n}.
Use 0 to deselect all.

@item key @code{n}
Toggle selection of subkey with index @code{n}.
Use 0 to deselect all.

@item check
Check all selected user ids.

@item showphoto
Display the selected photographic user
id.

@item pref
List preferences from the selected user ID. This shows the actual
preferences, without including any implied preferences.

@item showpref
More verbose preferences listing for the selected user ID. This shows
the preferences in effect by including the implied preferences of
3DES (cipher), SHA-1 (digest), and Uncompressed (compression) if they
are not already included in the preference list.

@item setpref @code{string}
Set the list of user ID preferences to @code{string}, this should be a
string similar to the one printed by "pref". Using an empty string
will set the default preference string, using "none" will set the
preferences to nil. Use "gpg -v ---version" to get a list of available
algorithms. This command just initializes an internal list and does
not change anything unless another command (such as "updpref") which
changes the self-signatures is used.

@item updpref
Change the preferences of all user IDs (or just of the selected ones
to the current list of preferences. The timestamp of all affected
self-signatures will be advanced by one second. Note that while you
can change the preferences on an attribute user ID (aka "photo ID"),
GnuPG does not select keys via attribute user IDs so these preferences
will not be used by GnuPG.

@item toggle
Toggle between public and secret key listing.

@item save
Save all changes to the key rings and quit.

@item quit
Quit the program without updating the
key rings.

@end table

The listing shows you the key with its secondary
keys and all user ids. Selected keys or user ids
are indicated by an asterisk. The trust value is
displayed with the primary key: the first is the
assigned owner trust and the second is the calculated
trust value. Letters are used for the values:

@table @asis
@item -
No ownertrust assigned / not yet calculated.

@item e
Trust
calculation has failed; probably due to an expired key.

@item q
Not enough information for calculation.

@item n
Never trust this key.

@item m
Marginally trusted.

@item f
Fully trusted.

@item u
Ultimately trusted.

@end table

@item ---sign-key @code{name}
Signs a public key with your secret key. This is a shortcut version of
the subcommand "sign" from ---edit.

@item ---lsign-key @code{name}
Signs a public key with your secret key but marks it as
non-exportable. This is a shortcut version of the subcommand "lsign"
from ---edit.

@item ---nrsign-key @code{name}
Signs a public key with your secret key but marks it as non-revocable.
This is a shortcut version of the subcommand "nrsign" from ---edit.

@item ---delete-key @code{name}
Remove key from the public keyring. In batch mode either ---yes is
required or the key must be specified by fingerprint. This is a
safeguard against accidental deletion of multiple keys.

@item ---delete-secret-key @code{name}
Remove key from the secret and public keyring. In batch mode the key
must be specified by fingerprint.

@item ---delete-secret-and-public-key @code{name}
Same as ---delete-key, but if a secret key exists, it will be removed 
first. In batch mode the key must be specified by fingerprint.

@item ---gen-revoke
Generate a revocation certificate for the complete key. To revoke
a subkey or a signature, use the ---edit command.

@item ---desig-revoke
Generate a designated revocation certificate for a key. This allows a
user (with the permission of the keyholder) to revoke someone elses
key.

@item ---export @code{names}
Either export all keys from all keyrings (default
keyrings and those registered via option ---keyring),
or if at least one name is given, those of the given
name. The new keyring is written to stdout or to
the file given with option "output". Use together
with ---armor to mail those keys.

@item ---send-keys @code{names}
Same as ---export but sends the keys to a keyserver.
Option ---keyserver must be used to give the name
of this keyserver. Don't send your complete keyring
to a keyserver - select only those keys which are new
or changed by you.

@item ---export-all @code{names}
Same as ---export, but also exports keys which
are not compatible with OpenPGP.

@item ---export-secret-keys @code{names}
@itemx ---export-secret-subkeys @code{names}
Same as ---export, but exports the secret keys instead.
This is normally not very useful and a security risk.
The second form of the command has the special property to
render the secret part of the primary key useless; this is
a GNU extension to OpenPGP and other implementations can
not be expected to successfully import such a key.
See the option ---simple-sk-checksum if you want to import such an
exported key with an older OpenPGP implementation.

@item ---import @code{files}
@itemx ---fast-import @code{files}
Import/merge keys. This adds the given keys to the
keyring. The fast version is currently just a synonym.

There are a few other options which control how this command works.
Most notable here is the ---merge-only option which does not insert new keys
but does only the merging of new signatures, user-IDs and subkeys.

@item ---recv-keys @code{key IDs}
Import the keys with the given key IDs from a keyserver. Option
---keyserver must be used to give the name of this keyserver.

@item ---refresh-keys @code{key IDs}
Request updates from a keyserver for keys that already exist on the
local keyring. This is useful for updating a key with the latest
signatures, user IDs, etc. Option ---keyserver must be used to give
the name of this keyserver.

@item ---search-keys @code{names}
Search the keyserver for the given names. Multiple names given here
will be joined together to create the search string for the keyserver.
Option ---keyserver must be used to give the name of this keyserver.

@item ---update-trustdb
Do trust DB maintenance. This command goes over all keys and builds
the Web-of-Trust. This is an interactive command because it may has to
ask for the "ownertrust" values of keys. The user has to give an
estimation in how far she trusts the owner of the displayed key to
correctly certify (sign) other keys. It does only ask for that value
if it has not yet been assigned to a key. Using the edit menu, that
value can be changed at any time later.

@item ---check-trustdb
Do trust DB maintenance without user interaction. Form time to time
the trust database must be updated so that expired keys and resulting
changes in the Web-of-Trust can be tracked. GnuPG tries to figure
when this is required and then does it implicitly; this command can be
used to force such a check. The processing is identically to that of
---update-trustdb but it skips keys with a not yet defined "ownertrust".

For use with cron jobs, this command can be used together with ---batch
in which case the check is only done when it is due. To force a run
even in batch mode add the option ---yes.

@item ---export-ownertrust @code{file}
Store the ownertrust values into
@code{file} (or stdin if not given). This is useful for backup
purposes as these values are the only ones which can't be re-created
from a corrupted trust DB.

@item ---import-ownertrust @code{files}
Update the trustdb with the ownertrust values stored
in @code{files} (or stdin if not given); existing
values will be overwritten.

@item ---rebuild-keydb-caches
When updating from version 1.0.6 to 1.0.7 this command should be used
to create signature caches in the keyring. It might be handy in other
situations too.

@item ---print-md @code{algo} @code{files}
@itemx ---print-mds @code{files}
Print message digest of algorithm ALGO for all given files or stdin.
With the second form (or a deprecated "*" as algo) digests for all
available algorithms are printed.

@item ---gen-random @code{0|1|2} @code{count}
Emit COUNT random bytes of the given quality level. If count is not given
or zero, an endless sequence of random bytes will be emitted.
PLEASE, don't use this command unless you know what you are doing; it may
remove precious entropy from the system!

@item ---gen-prime @code{mode} @code{bits} @code{qbits}
Use the source, Luke :-). The output format is still subject to change.

@item ---version
Print version information along with a list
of supported algorithms.

@item ---warranty
Print warranty information.

@item -h, ---help
Print usage information. This is a really long list even though it doesn't list
all options.

@end table

@majorheading OPTIONS
Long options can be put in an options file (default
"~/.gnupg/gpg.conf"). Short option names will not work - for example,
"armor" is a valid option for the options file, while "a" is not. Do
not write the 2 dashes, but simply the name of the option and any
required arguments. Lines with a hash ('#') as the first
non-white-space character are ignored. Commands may be put in this
file too, but that does not make sense.

@code{gpg} recognizes these options:

@table @asis
@item -a, ---armor
Create ASCII armored output.

@item -o, ---output @code{file}
Write output to @code{file}.

@item ---no-mangle-dos-filenames
@itemx ---mangle-dos-filenames
The Windows version of GPG replaces the extension of an output
filename to avoid problems with filenames containing more than one
dot. This is not necessary for newer Windows version and such
---no-mangle-dos-filenames can be used to switch this feature off and 
have GPG append the new extension. This otion has no effect on
non-windows platforms.

@item -u, ---local-user @code{name}
Use @code{name} as the user ID to sign.
This option is silently ignored for the list commands,
so that it can be used in an options file.

@item ---default-key @code{name}
Use @code{name} as default user ID for signatures. If this
is not used the default user ID is the first user ID
found in the secret keyring.

@item -r, ---recipient @code{name}
@itemx 
Encrypt for user id @code{name}. If this option is not
specified, GnuPG asks for the user-id unless ---default-recipient is given

@item ---default-recipient @code{name}
Use @code{name} as default recipient if option ---recipient is not used and
don't ask if this is a valid one. @code{name} must be non-empty.

@item ---default-recipient-self
Use the default key as default recipient if option ---recipient is not used and
don't ask if this is a valid one. The default key is the first one from the
secret keyring or the one set with ---default-key.

@item ---no-default-recipient
Reset ---default-recipient and --default-recipient-self.

@item ---encrypt-to @code{name}
Same as ---recipient but this one is intended for use
in the options file and may be used with
your own user-id as an "encrypt-to-self". These keys
are only used when there are other recipients given
either by use of ---recipient or by the asked user id.
No trust checking is performed for these user ids and
even disabled keys can be used.

@item ---no-encrypt-to
Disable the use of all ---encrypt-to keys.

@item -v, ---verbose
Give more information during processing. If used
twice, the input data is listed in detail.

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

@item -z @code{n}, ---compress @code{n}
Set compression level to @code{n}. A value of 0 for @code{n}
disables compression. Default is to use the default
compression level of zlib (normally 6).

@item -t, ---textmode
Use canonical text mode. If -t (but not
---textmode) is used together with armoring
and signing, this enables clearsigned messages.
This kludge is needed for PGP compatibility;
normally you would use ---sign or --clearsign
to selected the type of the signature.

@item -n, ---dry-run
Don't make any changes (this is not completely implemented).

@item -i, ---interactive
Prompt before overwriting any files.

@item ---batch
Use batch mode. Never ask, do not allow interactive
commands.

@item ---no-tty
Make sure that the TTY (terminal) is never used for any output.
This option is needed in some cases because GnuPG sometimes prints
warnings to the TTY if ---batch is used.

@item ---no-batch
Disable batch mode. This may be of use if ---batch
is enabled from an options file.

@item ---yes
Assume "yes" on most questions.

@item ---no
Assume "no" on most questions.

@item ---default-cert-check-level @code{n}
The default to use for the check level when signing a key.

0 means you make no particular claim as to how carefully you verified
the key.

1 means you believe the key is owned by the person who claims to own
it but you could not, or did not verify the key at all. This is
useful for a "persona" verification, where you sign the key of a
pseudonymous user.

2 means you did casual verification of the key. For example, this
could mean that you verified that the key fingerprint and checked the
user ID on the key against a photo ID.

3 means you did extensive verification of the key. For example, this
could mean that you verified the key fingerprint with the owner of the
key in person, and that you checked, by means of a hard to forge
document with a photo ID (such as a passport) that the name of the key
owner matches the name in the user ID on the key, and finally that you
verified (by exchange of email) that the email address on the key
belongs to the key owner.

Note that the examples given above for levels 2 and 3 are just that:
examples. In the end, it is up to you to decide just what "casual"
and "extensive" mean to you.

This option defaults to 0.

@item ---trusted-key @code{long key ID}
Assume that the specified key (which must be given
as a full 8 byte key ID) is as trustworthy as one of
your own secret keys. This option is useful if you
don't want to keep your secret keys (or one of them)
online but still want to be able to check the validity of a given
recipient's or signator's key. 

@item ---trust-model @code{classic|always}
Set what trust model GnuPG should follow. The models are:

@table @asis
@item classic
This is the regular web-of-trust as used in PGP and GnuPG.

@item always
Skip key validation and assume that used keys are always fully
trusted. You won't use this unless you have installed some external
validation scheme. This option also suppresses the "[uncertain]" tag
printed with signature checks when there is no evidence that the user
ID is bound to the key.

@end table

@item ---always-trust
Identical to `---trust-model always'

@item ---keyserver @code{name}
Use @code{name} as your keyserver. This is the server that ---recv-keys,
---send-keys, and --search-keys will communicate with to receive keys
from, send keys to, and search for keys on. The format of the
@code{name} is a URI: `scheme:[//]keyservername[:port]' The scheme is
the type of keyserver: "hkp" for the Horowitz (or compatible)
keyservers, "ldap" for the NAI LDAP keyserver, or "mailto" for the
Horowitz email keyserver. Note that your particular installation of
GnuPG may have other keyserver types available as well. Keyserver
schemes are case-insensitive.

Most keyservers synchronize with each other, so there is generally no
need to send keys to more than one server. Using the command "host -l
pgp.net | grep wwwkeys" gives you a list of HKP keyservers. When
using one of the wwwkeys servers, due to load balancing using
round-robin DNS you may notice that you get a different key server
each time.

@item ---keyserver-options @code{parameters}
This is a space or comma delimited string that gives options for the
keyserver. Options can be prepended with a `no-' to give the opposite
meaning. Valid import-options or export-options may be used here as
well to apply to importing (---recv-key) or exporting (--send-key) a
key from a keyserver. While not all options are available for all
keyserver types, some common options are:

@table @asis
@item include-revoked
When searching for a key with ---search-keys, include keys that are
marked on the keyserver as revoked. Note that this option is always
set when using the NAI HKP keyserver, as this keyserver does not
differentiate between revoked and unrevoked keys.

@item include-disabled
When searching for a key with ---search-keys, include keys that are
marked on the keyserver as disabled. Note that this option is not
used with HKP keyservers.

@item include-subkeys
When receiving a key, include subkeys as potential targets. Note that
this option is not used with HKP keyservers, as they do not support
retrieving keys by subkey id.

@item use-temp-files
On most Unix-like platforms, GnuPG communicates with the keyserver
helper program via pipes, which is the most efficient method. This
option forces GnuPG to use temporary files to communicate. On some
platforms (such as Win32 and RISC OS), this option is always enabled.

@item keep-temp-files
If using `use-temp-files', do not delete the temp files after using
them. This option is useful to learn the keyserver communication
protocol by reading the temporary files.

@item verbose
Tell the keyserver helper program to be more verbose. This option can
be repeated multiple times to increase the verbosity level.

@item honor-http-proxy
For keyserver schemes that use HTTP (such as HKP), try to access the
keyserver over the proxy set with the environment variable
"http_proxy".

@item auto-key-retrieve
This option enables the automatic retrieving of keys from a keyserver
when verifying signatures made by keys that are not on the local
keyring.

@end table

@item ---import-options @code{parameters}
This is a space or comma delimited string that gives options for
importing keys. Options can be prepended with a `no-' to give the
opposite meaning. The options are:

@table @asis
@item allow-local-sigs
Allow importing key signatures marked as "local". This is not
generally useful unless a shared keyring scheme is being used.
Defaults to no.

@item repair-hkp-subkey-bug
During import, attempt to repair the HKP keyserver mangling multiple
subkeys bug. Note that this cannot completely repair the damaged key
as some crucial data is removed by the keyserver, but it does at least
give you back one subkey. Defaults to no for regular ---import and to
yes for keyserver ---recv-keys.

@end table

@item ---export-options @code{parameters}
This is a space or comma delimited string that gives options for
exporting keys. Options can be prepended with a `no-' to give the
opposite meaning. The options are:

@table @asis
@item include-non-rfc
Include non-RFC compliant keys in the export. Defaults to yes.

@item include-local-sigs
Allow exporting key signatures marked as "local". This is not
generally useful unless a shared keyring scheme is being used.
Defaults to no.

@item include-attributes
Include attribute user IDs (photo IDs) while exporting. This is
useful to export keys if they are going to be used by an OpenPGP
program that does not accept attribute user IDs. Defaults to yes.

@item include-sensitive-revkeys
Include designated revoker information that was marked as
"sensitive". Defaults to no.

@end table

@item ---show-photos
Causes ---list-keys, --list-sigs, --list-public-keys,
---list-secret-keys, and verifying a signature to also display the
photo ID attached to the key, if any.
See also ---photo-viewer.

@item ---no-show-photos
Resets the ---show-photos flag.

@item ---photo-viewer @code{string}
This is the command line that should be run to view a photo ID. "%i"
will be expanded to a filename containing the photo. "%I" does the
same, except the file will not be deleted once the viewer exits.
Other flags are "%k" for the key ID, "%K" for the long key ID, "%f"
for the key fingerprint, "%t" for the extension of the image type
(e.g. "jpg"), "%T" for the MIME type of the image (e.g. "image/jpeg"),
and "%%" for an actual percent sign. If neither %i or %I are present,
then the photo will be supplied to the viewer on standard input.

The default viewer is "xloadimage -fork -quiet -title 'KeyID 0x%k'
stdin"

@item ---exec-path @code{string}
Sets a list of directories to search for photo viewers and keyserver
helpers. If not provided, keyserver helpers use the compiled-in
default directory, and photo viewers use the $PATH environment
variable.

@item ---show-keyring
Causes ---list-keys, --list-public-keys, and --list-secret-keys to
display the name of the keyring a given key resides on. This is only
useful when you're listing a specific key or set of keys. It has no
effect when listing all keys.

@item ---keyring @code{file}
Add @code{file} to the list of keyrings.
If @code{file} begins with a tilde and a slash, these
are replaced by the HOME directory. If the filename
does not contain a slash, it is assumed to be in the
home-directory ("~/.gnupg" if ---homedir is not used).
The filename may be prefixed with a scheme:

"gnupg-ring:" is the default one.

It might make sense to use it together with ---no-default-keyring.

@item ---secret-keyring @code{file}
Same as ---keyring but for the secret keyrings.

@item ---homedir @code{directory}
Set the name of the home directory to @code{directory} If this
option is not used it defaults to "~/.gnupg". It does
not make sense to use this in a options file. This
also overrides the environment variable "GNUPGHOME".

@item ---charset @code{name}
Set the name of the native character set. This is used
to convert some strings to proper UTF-8 encoding. If this option is not used, the default character set is determined
from the current locale. A verbosity level of 3 shows the used one.
Valid values for @code{name} are:

@table @asis
@item iso-8859-1
This is the Latin 1 set.

@item iso-8859-2
The Latin 2 set.

@item iso-8859-15
This is currently an alias for
the Latin 1 set.

@item koi8-r
The usual Russian set (rfc1489).

@item utf-8
Bypass all translations and assume
that the OS uses native UTF-8 encoding.

@end table

@item ---utf8-strings
@itemx ---no-utf8-strings
Assume that the arguments are already given as UTF8 strings. The default
(---no-utf8-strings)
is to assume that arguments are encoded in the character set as specified
by ---charset. These options affect all following arguments. Both options may
be used multiple times.

@item ---options @code{file}
Read options from @code{file} and do not try to read
them from the default options file in the homedir
(see ---homedir). This option is ignored if used
in an options file.

@item ---no-options
Shortcut for "---options /dev/null". This option is
detected before an attempt to open an option file.
Using this option will also prevent the creation of a 
"~./gnupg" homedir.

@item ---load-extension @code{name}
Load an extension module. If @code{name} does not contain a slash it is
searched for in the directory configured when GnuPG was built
(generally "/usr/local/lib/gnupg"). Extensions are not generally
useful anymore, and the use of this option is deprecated.

@item ---debug @code{flags}
Set debugging flags. All flags are or-ed and @code{flags} may
be given in C syntax (e.g. 0x0042).

@item ---debug-all
Set all useful debugging flags.

@item ---status-fd @code{n}
Write special status strings to the file descriptor @code{n}.
See the file DETAILS in the documentation for a listing of them.

@item ---logger-fd @code{n}
Write log output to file descriptor @code{n} and not to stderr.

@item ---attribute-fd @code{n}
Write attribute subpackets to the file descriptor @code{n}. This is
most useful for use with ---status-fd, since the status messages are
needed to separate out the various subpackets from the stream
delivered to the file descriptor.

@item ---sk-comments
Include secret key comment packets when exporting secret keys. This
is a GnuPG extension to the OpenPGP standard, and is off by default.
Please note that this has nothing to do with the comments in clear
text signatures or armor headers.

@item ---no-sk-comments
Resets the ---sk-comments option.

@item ---no-comment
See ---sk-comments. This option is deprecated and may be removed soon.

@item ---comment @code{string}
Use @code{string} as comment string in clear text signatures.
The default is not do write a comment string.

@item ---default-comment
Force to write the standard comment string in clear
text signatures. Use this to overwrite a ---comment
from a config file. This option is now obsolete because there is no
default comment string anymore.

@item ---no-version
Omit the version string in clear text signatures.

@item ---emit-version
Force to write the version string in clear text
signatures. Use this to overwrite a previous
---no-version from a config file.

@item ---sig-notation @code{name=value}
@itemx ---cert-notation @code{name=value}
@itemx -N, ---notation-data @code{name=value}
Put the name value pair into the signature as notation data.
@code{name} must consist only of printable characters or spaces, and
must contain a '@@' character. This is to help prevent pollution of
the IETF reserved notation namespace. The ---expert flag overrides the
'@@' check. @code{value} may be any printable string; it will be
encoded in UTF8, so you should check that your ---charset is set
correctly. If you prefix @code{name} with an exclamation mark, the
notation data will be flagged as critical (rfc2440:5.2.3.15).
---sig-notation sets a notation for data signatures. --cert-notation
sets a notation for key signatures (certifications). ---notation-data
sets both.

There are special codes that may be used in notation names. "%k" will
be expanded into the key ID of the key being signed, "%K" for the long
key ID of the key being signed, "%f" for the key fingerprint of the
key being signed, "%s" for the key ID of the key making the signature,
"%S" for the long key ID of the key making the signature, and "%%"
results in a single "%". %k, %K, and %f are only meaningful when
making a key signature (certification).

@item ---show-notation
Show signature notations in the ---list-sigs or --check-sigs listings
as well as when verifying a signature with a notation in it.

@item ---no-show-notation
Do not show signature notations.

@item ---sig-policy-url @code{string}
@itemx ---cert-policy-url @code{string}
@itemx ---set-policy-url @code{string}
Use @code{string} as Policy URL for signatures (rfc2440:5.2.3.19). If
you prefix it with an exclamation mark, the policy URL packet will be
flagged as critical. ---sig-policy-url sets a a policy url for data
signatures. ---cert-policy-url sets a policy url for key signatures
(certifications). -set-policy-url sets both.

The same %-expandos used for notation data are available here as well.

@item ---show-policy-url
Show policy URLs in the ---list-sigs or --check-sigs listings as well
as when verifying a signature with a policy URL in it.

@item ---no-show-policy-url
Do not show policy URLs.

@item ---set-filename @code{string}
Use @code{string} as the name of file which is stored in
messages.

@item ---for-your-eyes-only
Set the `for your eyes only' flag in the message. This causes GnuPG
to refuse to save the file unless the ---output option is given, and
PGP to use the "secure viewer" with a Tempest-resistant font to
display the message. This option overrides ---set-filename.

@item ---no-for-your-eyes-only
Resets the ---for-your-eyes-only flag.

@item ---use-embedded-filename
Try to create a file with a name as embedded in the data.
This can be a dangerous option as it allows to overwrite files.

@item ---completes-needed @code{n}
Number of completely trusted users to introduce a new
key signer (defaults to 1).

@item ---marginals-needed @code{n}
Number of marginally trusted users to introduce a new
key signer (defaults to 3)

@item ---max-cert-depth @code{n}
Maximum depth of a certification chain (default is 5).

@item ---cipher-algo @code{name}
Use @code{name} as cipher algorithm. Running the program
with the command ---version yields a list of supported
algorithms. If this is not used the cipher algorithm is
selected from the preferences stored with the key.

@item ---digest-algo @code{name}
Use @code{name} as the message digest algorithm. Running the program
with the command ---version yields a list of supported algorithms.

@item ---cert-digest-algo @code{name}
Use @code{name} as the message digest algorithm used when signing a
key. Running the program with the command ---version yields a list of
supported algorithms. Be aware that if you choose an algorithm that
GnuPG supports but other OpenPGP implementations do not, then some
users will not be able to use the key signatures you make, or quite
possibly your entire key.

@item ---s2k-cipher-algo @code{name}
Use @code{name} as the cipher algorithm used to protect secret keys.
The default cipher is CAST5. This cipher is also used for
conventional encryption if ---cipher-algo is not given.

@item ---s2k-digest-algo @code{name}
Use @code{name} as the digest algorithm used to mangle the passphrases.
The default algorithm is SHA-1. This digest algorithm is also used
for conventional encryption if ---digest-algo is not given.

@item ---s2k-mode @code{n}
Selects how passphrases are mangled. If @code{n} is 0 a plain
passphrase (which is not recommended) will be used, a 1 adds a salt to
the passphrase and a 3 (the default) iterates the whole process a
couple of times. Unless ---rfc1991 is used, this mode is also used for
conventional encryption.

@item ---simple-sk-checksum
Secret keys are integrity protected by using a SHA-1 checksum. This
method will be part of an enhanced OpenPGP specification but GnuPG
already uses it as a countermeasure against certain attacks. Old
applications don't understand this new format, so this option may be
used to switch back to the old behaviour. Using this this option
bears a security risk. Note that using this option only takes effect
when the secret key is encrypted - the simplest way to make this
happen is to change the passphrase on the key (even changing it to the
same value is acceptable).

@item ---compress-algo @code{n}
Use compression algorithm @code{n}. The value 2 is RFC1950 ZLIB
compression. The value 1 is RFC-1951 ZIP compression which is used by
PGP. 0 disables compression. If this option is not used, the default
behavior is to examine the recipient key preferences to see which
algorithms the recipient supports. If all else fails, ZIP is used for
maximum compatibility. Note, however, that ZLIB may give better
compression results if that is more important, as the compression
window size is not limited to 8k.

@item ---disable-cipher-algo @code{name}
Never allow the use of @code{name} as cipher algorithm.
The given name will not be checked so that a later loaded algorithm
will still get disabled.

@item ---disable-pubkey-algo @code{name}
Never allow the use of @code{name} as public key algorithm.
The given name will not be checked so that a later loaded algorithm
will still get disabled.

@item ---no-sig-cache
Do not cache the verification status of key signatures.
Caching gives a much better performance in key listings. However, if
you suspect that your public keyring is not save against write
modifications, you can use this option to disable the caching. It
probably does not make sense to disable it because all kind of damage
can be done if someone else has write access to your public keyring.

@item ---no-sig-create-check
GnuPG normally verifies each signature right after creation to protect
against bugs and hardware malfunctions which could leak out bits from
the secret key. This extra verification needs some time (about 115%
for DSA keys), and so this option can be used to disable it.
However, due to the fact that the signature creation needs manual
interaction, this performance penalty does not matter in most settings.

@item ---auto-check-trustdb
If GnuPG feels that its information about the Web-of-Trust has to be
updated, it automatically runs the ---check-trustdb command 
internally. This may be a time consuming process.

@item ---no-auto-check-trustdb
Resets the ---auto-check-trustdb option.

@item ---throw-keyid
Do not put the keyid into encrypted packets. This option
hides the receiver of the message and is a countermeasure
against traffic analysis. It may slow down the decryption
process because all available secret keys are tried.

@item ---not-dash-escaped
This option changes the behavior of cleartext signatures
so that they can be used for patch files. You should not
send such an armored file via email because all spaces
and line endings are hashed too. You can not use this
option for data which has 5 dashes at the beginning of a
line, patch files don't have this. A special armor header
line tells GnuPG about this cleartext signature option.

@item ---escape-from-lines
Because some mailers change lines starting with "From "
to "<From " it is good to handle such lines in a special
way when creating cleartext signatures. All other PGP
versions do it this way too. This option is not enabled
by default because it would violate rfc2440.

@item ---passphrase-fd @code{n}
Read the passphrase from file descriptor @code{n}. If you use
0 for @code{n}, the passphrase will be read from stdin. This
can only be used if only one passphrase is supplied.
Don't use this option if you can avoid it.

@item ---command-fd @code{n}
This is a replacement for the deprecated shared-memory IPC mode.
If this option is enabled, user input on questions is not expected
from the TTY but from the given file descriptor. It should be used
together with ---status-fd. See the file doc/DETAILS in the source
distribution for details on how to use it.

@item ---use-agent
Try to use the GnuPG-Agent. Please note that this agent is still under
development. With this option, GnuPG first tries to connect to the
agent before it asks for a passphrase.

@item ---gpg-agent-info
Override the value of the environment variable
@samp{GPG_AGENT_INFO}. This is only used when ---use-agent has been given

@item ---rfc1991
Try to be more RFC1991 (PGP 2.x) compliant.

@item ---pgp2
Set up all options to be as PGP 2.x compliant as possible, and warn if
an action is taken (e.g. encrypting to a non-RSA key) that will create
a message that PGP 2.x will not be able to handle. Note that `PGP
2.x' here means `MIT PGP 2.6.2'. There are other versions of PGP 2.x
available, but the MIT release is a good common baseline.

This option implies `---rfc1991 --no-openpgp --disable-mdc
---no-force-v4-certs --no-comment --escape-from-lines --force-v3-sigs
---no-ask-sig-expire --no-ask-cert-expire --cipher-algo IDEA
---digest-algo MD5 --compress-algo 1'. It also disables --textmode
when encrypting.

@item ---no-pgp2
Resets the ---pgp2 option.

@item ---pgp6
Set up all options to be as PGP 6 compliant as possible. This
restricts you to the ciphers IDEA (if the IDEA plugin is installed),
3DES, and CAST5, the hashes MD5, SHA1 and RIPEMD160, and the
compression algorithms none and ZIP. This also disables
---throw-keyid, and making signatures with signing subkeys as PGP 6
does not understand signatures made by signing subkeys.

This option implies `---disable-mdc --no-comment --escape-from-lines
---force-v3-sigs --no-ask-sig-expire --compress-algo 1'

@item ---no-pgp6
Resets the ---pgp6 option.

@item ---pgp7
Set up all options to be as PGP 7 compliant as possible. This is
identical to ---pgp6 except that MDCs are not disabled, and the list of
allowable ciphers is expanded to add AES128, AES192, AES256, and
TWOFISH.

@item ---no-pgp7
Resets the ---pgp7 option.

@item ---pgp8
Set up all options to be as PGP 8 compliant as possible. PGP 8 is a
lot closer to the OpenPGP standard than previous versions of PGP, so
all this does is disable ---throw-keyid and set --escape-from-lines and
---compress-algo 1. The allowed algorithms list is the same as --pgp7.

@item ---no-pgp8
Resets the ---pgp8 option.

@item ---openpgp
Reset all packet, cipher and digest options to OpenPGP behavior. Use
this option to reset all previous options like ---rfc1991,
---force-v3-sigs, --s2k-*, --cipher-algo, --digest-algo and
---compress-algo to OpenPGP compliant values. All PGP workarounds are
also disabled.

@item ---force-v3-sigs
OpenPGP states that an implementation should generate v4 signatures
but PGP versions 5 and higher only recognize v4 signatures on key
material. This option forces v3 signatures for signatures on data.
Note that this option overrides ---ask-sig-expire, as v3 signatures
cannot have expiration dates.

@item ---no-force-v3-sigs
Reset the ---force-v3-sigs option.

@item ---force-v4-certs
Always use v4 key signatures even on v3 keys. This option also
changes the default hash algorithm for v3 RSA keys from MD5 to SHA-1.

@item ---no-force-v4-certs
Reset the ---force-v4-certs option.

@item ---force-mdc
Force the use of encryption with a modification detection code. This
is always used with the newer ciphers (those with a blocksize greater
than 64 bits), or if the recipient key has one of those ciphers as a
preference.

@item ---disable-mdc
Disable the use of the modification detection code. Note that by
using this option, the encrypted message becomes vulnerable to a
message modification attack.

@item ---allow-non-selfsigned-uid
Allow the import and use of keys with user IDs which are not
self-signed. This is not recommended, as a non self-signed user ID is
trivial to forge.

@item ---no-allow-non-selfsigned-uid
Reset the ---allow-non-selfsigned-uid option.

@item ---allow-freeform-uid
Disable all checks on the form of the user ID while generating a new
one. This option should only be used in very special environments as
it does not ensure the de-facto standard format of user IDs.

@item ---ignore-time-conflict
GnuPG normally checks that the timestamps associated with keys and
signatures have plausible values. However, sometimes a signature seems to
be older than the key due to clock problems. This option makes these
checks just a warning.

@item ---ignore-valid-from
GnuPG normally does not select and use subkeys created in the future. This
option allows the use of such keys and thus exhibits the pre-1.0.7
behaviour. You should not use this option unless you there is some
clock problem.

@item ---ignore-crc-error
The ASCII armor used by OpenPGP is protected by a CRC checksum against
transmission errors. Sometimes it happens that the CRC gets mangled
somewhere on the transmission channel but the actual content (which is
protected by the OpenPGP protocol anyway) is still okay. This option
will let gpg ignore CRC errors.

@item ---ignore-mdc-error
This option changes a MDC integrity protection failure into a warning.
This can be useful if a message is partially corrupt, but it is
necessary to get as much data as possible out of the corrupt message.
However, be aware that a MDC protection failure may also mean that the
message was tampered with intentionally by an attacker.

@item ---lock-once
Lock the databases the first time a lock is requested
and do not release the lock until the process
terminates.

@item ---lock-multiple
Release the locks every time a lock is no longer
needed. Use this to override a previous ---lock-once
from a config file.

@item ---lock-never
Disable locking entirely. This option should be used only in very
special environments, where it can be assured that only one process
is accessing those files. A bootable floppy with a stand-alone
encryption system will probably use this. Improper usage of this
option may lead to data and key corruption.

@item ---no-random-seed-file
GnuPG uses a file to store its internal random pool over invocations.
This makes random generation faster; however sometimes write operations
are not desired. This option can be used to achieve that with the cost of
slower random generation.

@item ---no-verbose
Reset verbose level to 0.

@item ---no-greeting
Suppress the initial copyright message but do not
enter batch mode.

@item ---no-secmem-warning
Suppress the warning about "using insecure memory".

@item ---no-permission-warning
Suppress the warning about unsafe file permissions. Note that the
file permission checks that GnuPG does are not intended to be
authoritative, rather they simply warn about certain common permission
problems. Do not assume that the lack of a warning means that your
system is secure.

@item ---no-mdc-warning
Suppress the warning about missing MDC integrity protection.

@item ---no-armor
Assume the input data is not in ASCII armored format.

@item ---no-default-keyring
Do not add the default keyrings to the list of
keyrings.

@item ---skip-verify
Skip the signature verification step. This may be
used to make the decryption faster if the signature
verification is not needed.

@item ---with-colons
Print key listings delimited by colons. Note, that the output will be
encoded in UTF-8 regardless of any ---charset setting.

@item ---with-key-data
Print key listings delimited by colons (like ---with-colons) and print the public key data.

@item ---with-fingerprint
Same as the command ---fingerprint but changes only the format of the output
and may be used together with another command.

@item ---fast-list-mode
Changes the output of the list commands to work faster; this is achieved
by leaving some parts empty. Some applications don't need the user ID and
the trust information given in the listings. By using this options they
can get a faster listing. The exact behaviour of this option may change
in future versions.

@item ---fixed-list-mode
Do not merge user ID and primary key in ---with-colon listing mode and
print all timestamps as seconds since 1970-01-01.

@item ---list-only
Changes the behaviour of some commands. This is like ---dry-run but
different in some cases. The semantic of this command may be extended in
the future. Currently it only skips the actual decryption pass and
therefore enables a fast listing of the encryption keys.

@item ---no-literal
This is not for normal use. Use the source to see for what it might be useful.

@item ---set-filesize
This is not for normal use. Use the source to see for what it might be useful.

@item ---emulate-md-encode-bug
GnuPG versions prior to 1.0.2 had a bug in the way a signature was encoded.
This options enables a workaround by checking faulty signatures again with
the encoding used in old versions. This may only happen for ElGamal signatures
which are not widely used.

@item ---show-session-key
Display the session key used for one message. See ---override-session-key
for the counterpart of this option.

We think that Key-Escrow is a Bad Thing; however the user should
have the freedom to decide whether to go to prison or to reveal the content of
one specific message without compromising all messages ever encrypted for one
secret key. DON'T USE IT UNLESS YOU ARE REALLY FORCED TO DO SO.

@item ---override-session-key @code{string} 
Don't use the public key but the session key @code{string}. The format of this
string is the same as the one printed by ---show-session-key. This option
is normally not used but comes handy in case someone forces you to reveal the
content of an encrypted message; using this option you can do this without
handing out the secret key.

@item ---ask-sig-expire
When making a data signature, prompt for an expiration time. If this
option is not specified, the expiration time is "never".

@item ---no-ask-sig-expire
Resets the ---ask-sig-expire option.

@item ---ask-cert-expire
When making a key signature, prompt for an expiration time. If this
option is not specified, the expiration time is "never".

@item ---no-ask-cert-expire
Resets the ---ask-cert-expire option.

@item ---expert
Allow the user to do certain nonsensical or "silly" things like
signing an expired or revoked key, or certain potentially incompatible
things like generating deprecated key types. This also disables
certain warning messages about potentially incompatible actions. As
the name implies, this option is for experts only. If you don't fully
understand the implications of what it allows you to do, leave this
off.

@item ---no-expert
Resets the ---expert option.

@item ---merge-only
Don't insert new keys into the keyrings while doing an import.

@item ---allow-secret-key-import
This is an obsolete option and is not used anywhere.

@item ---try-all-secrets
Don't look at the key ID as stored in the message but try all secret keys in
turn to find the right decryption key. This option forces the behaviour as
used by anonymous recipients (created by using ---throw-keyid) and might come
handy in case where an encrypted message contains a bogus key ID.

@item ---enable-special-filenames
This options enables a mode in which filenames of the form
@file{-&n}, where n is a non-negative decimal number,
refer to the file descriptor n and not to a file with that name.

@item ---no-expensive-trust-checks
Experimental use only.

@item ---group @code{name=value1 value2 value3 ...}
Sets up a named group, which is similar to aliases in email programs.
Any time the group name is a receipient (-r or ---recipient), it will
be expanded to the values specified.

The values are @code{key IDs} or fingerprints, but any key description
is accepted. Note that a value with spaces in it will be treated as
two different values. Note also there is only one level of expansion
- you cannot make an group that points to another group. When used
from the command line, it may be necessary to quote the argument to
this option to prevent the shell from treating it as multiple
arguments.

@item ---preserve-permissions
Don't change the permissions of a secret keyring back to user
read/write only. Use this option only if you really know what you are doing.

@item ---personal-cipher-preferences @code{string}
Set the list of personal cipher preferences to @code{string}, this list
should be a string similar to the one printed by the command "pref" in
the edit menu. This allows the user to factor in their own preferred
algorithms when algorithms are chosen via recipient key preferences.

@item ---personal-digest-preferences @code{string}
Set the list of personal digest preferences to @code{string}, this list
should be a string similar to the one printed by the command "pref" in
the edit menu. This allows the user to factor in their own preferred
algorithms when algorithms are chosen via recipient key preferences.

@item ---personal-compress-preferences @code{string}
Set the list of personal compression preferences to @code{string}, this
list should be a string similar to the one printed by the command
"pref" in the edit menu. This allows the user to factor in their own
preferred algorithms when algorithms are chosen via recipient key
preferences.

@item ---default-preference-list @code{string}
Set the list of default preferences to @code{string}, this list should
be a string similar to the one printed by the command "pref" in the
edit menu. This affects both key generation and "updpref" in the edit
menu.

@end table

@majorheading How to specify a user ID
There are different ways on how to specify a user ID to GnuPG;
here are some examples:

@table @asis
@item 
@item 234567C4
@itemx 0F34E556E
@itemx 01347A56A
@itemx 0xAB123456
Here the key ID is given in the usual short form.

@item 234AABBCC34567C4
@itemx 0F323456784E56EAB
@itemx 01AB3FED1347A5612
@itemx 0x234AABBCC34567C4
Here the key ID is given in the long form as used by OpenPGP
(you can get the long key ID using the option ---with-colons).

@item 1234343434343434C434343434343434
@itemx 123434343434343C3434343434343734349A3434
@itemx 0E12343434343434343434EAB3484343434343434
@itemx 0xE12343434343434343434EAB3484343434343434
The best way to specify a key ID is by using the fingerprint of
the key. This avoids any ambiguities in case that there are duplicated
key IDs (which are really rare for the long key IDs).

@item =Heinrich Heine <heinrichh@@uni-duesseldorf.de>
Using an exact to match string. The equal sign indicates this.

@item <heinrichh@@uni-duesseldorf.de>
Using the email address part which must match exactly. The left angle bracket
indicates this email address mode.

@item +Heinrich Heine duesseldorf
All words must match exactly (not case sensitive) but can appear in
any order in the user ID. Words are any sequences of letters,
digits, the underscore and all characters with bit 7 set.

@item Heine
@itemx *Heine
By case insensitive substring matching. This is the default mode but
applications may want to explicitly indicate this by putting the asterisk
in front.

@end table

Note that you can append an exclamation mark to key IDs or
fingerprints. This flag tells GnuPG to use exactly the given primary
or secondary key and not to try to figure out which secondary or
primary key to use.

@majorheading RETURN VALUE
The program returns 0 if everything was fine, 1 if at least
a signature was bad, and other error codes for fatal errors.

@majorheading EXAMPLES
@table @asis
@item gpg -se -r @code{Bob} @code{file}
sign and encrypt for user Bob

@item gpg ---clearsign @code{file}
make a clear text signature

@item gpg -sb @code{file}
make a detached signature

@item gpg ---list-keys @code{user_ID}
show keys

@item gpg ---fingerprint @code{user_ID}
show fingerprint

@item gpg ---verify @code{pgpfile}
@itemx gpg ---verify @code{sigfile} @code{files}
Verify the signature of the file but do not output the data. The second form
is used for detached signatures, where @code{sigfile} is the detached
signature (either ASCII armored of binary) and @code{files} are the signed
data; if this is not given the name of the file holding the signed data is
constructed by cutting off the extension (".asc" or ".sig") of
@code{sigfile} or by asking the user for the filename.

@end table

@majorheading ENVIRONMENT
@table @asis
@item HOME
Used to locate the default home directory.

@item GNUPGHOME
If set directory used instead of "~/.gnupg".

@item GPG_AGENT_INFO
Used to locate the gpg-agent; only honored when
---use-agent is set. The value consists of 3 colon delimited fields: 
The first is the path to the Unix Domain Socket, the second the PID of
the gpg-agent and the protocol version which should be set to 1. When
starting the gpg-agent as described in its documentation, this
variable is set to the correct value. The option ---gpg-agent-info can
be used to override it.

@item http_proxy
Only honored when the keyserver-option
honor-http-proxy is set.

@end table

@majorheading FILES
@table @asis
@item ~/.gnupg/secring.gpg
The secret keyring

@item ~/.gnupg/secring.gpg.lock
and the lock file

@item ~/.gnupg/pubring.gpg
The public keyring

@item ~/.gnupg/pubring.gpg.lock
and the lock file

@item ~/.gnupg/trustdb.gpg
The trust database

@item ~/.gnupg/trustdb.gpg.lock
and the lock file

@item ~/.gnupg/random_seed
used to preserve the internal random pool

@item ~/.gnupg/gpg.conf
Default configuration file

@item ~/.gnupg/options
Old style configuration file; only used when gpg.conf
is not found

@item /usr[/local]/share/gnupg/options.skel
Skeleton options file

@item /usr[/local]/lib/gnupg/
Default location for extensions

@end table

@majorheading WARNINGS
Use a *good* password for your user account and a *good* passphrase
to protect your secret key. This passphrase is the weakest part of the
whole system. Programs to do dictionary attacks on your secret keyring
are very easy to write and so you should protect your "~/.gnupg/"
directory very well.

Keep in mind that, if this program is used over a network (telnet), it
is *very* easy to spy out your passphrase!

If you are going to verify detached signatures, make sure that the
program knows about it; either be giving both filenames on the
command line or using @samp{-} to specify stdin.

@majorheading INTEROPERABILITY WITH OTHER OPENPGP PROGRAMS
GnuPG tries to be a very flexible implementation of the OpenPGP
standard. In particular, GnuPG implements many of the "optional"
parts of the standard, such as the RIPEMD/160 hash, and the ZLIB
compression algorithms. It is important to be aware that not all
OpenPGP programs implement these optional algorithms and that by
forcing their use via the ---cipher-algo, --digest-algo,
---cert-digest-algo, or --compress-algo options in GnuPG, it is
possible to create a perfectly valid OpenPGP message, but one that
cannot be read by the intended recipient.

For example, as of this writing, no version of official PGP supports
the BLOWFISH cipher algorithm. If you use it, no PGP user will be
able to decrypt your message. The same thing applies to the ZLIB
compression algorithm. By default, GnuPG will do the right thing and
create messages that are usable by any OpenPGP program. Only override
this safe default if you know what you are doing.

If you absolutely must override the safe default, you are far better
off using the ---pgp2, --pgp6, or --pgp7 options. These options are
safe as they do not force any particular algorithms in violation of
OpenPGP, but rather reduce the available algorithms to a "PGP-safe"
list.

@majorheading BUGS
On many systems this program should be installed as setuid(root). This
is necessary to lock memory pages. Locking memory pages prevents the
operating system from writing memory pages to disk. If you get no
warning message about insecure memory your operating system supports
locking without being root. The program drops root privileges as soon
as locked memory is allocated.

@bye