GPG2

NAME

SYNOPSIS

DESCRIPTION

In contrast to the standalone version gpg, which is more suited for server and embedded platforms, this version is installed under the name gpg2 and more targeted to the desktop as it requires several other modules to be installed. The standalone version will be kept maintained and it is possible to install both versions on the same system. If you need to use different configuration files, you should make use of something like oqgpg.conf-2cq instead of just oqgpg.confcq.

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.

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 give both filenames on the command line or use aq-aq to specify STDIN.

INTEROPERABILITY

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 SHA-512 hash, and the ZLIB and BZIP2 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.

There are dozens of variations of OpenPGP programs available, and each supports a slightly different subset of these optional algorithms. For example, until recently, no (unhacked) version of PGP supported the BLOWFISH cipher algorithm. A message using BLOWFISH simply could not be read by a PGP user. By default, GnuPG uses the standard OpenPGP preferences system that will always do the right thing and create messages that are usable by all recipients, regardless of which OpenPGP program they use. Only override this safe default if you really know what you are doing.

If you absolutely must override the safe default, or if the preferences on a given key are invalid for some reason, you are far better off using the --pgp6, --pgp7, or --pgp8 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.

COMMANDS

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

gpg2 may be run with no commands, in which case it will perform a reasonable action depending on the type of file it is given as input (an encrypted message is decrypted, a signature is verified, a file containing keys is listed).

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

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.

--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

--sign

-s

Make a signature. This command may be combined with --encrypt (for a signed and encrypted message), --symmetric (for a signed and symmetrically encrypted message), or --encrypt and --symmetric together (for a signed message that may be decrypted via a secret key or a passphrase). The key to be used for signing is chosen by default or can be set with the --local-user and --default-key options.

--clearsign

Make a clear text signature. The content in a clear text signature is readable without any special software. OpenPGP software is only needed to verify the signature. Clear text signatures may modify end-of-line whitespace for platform independence and are not intended to be reversible. The key to be used for signing is chosen by default or can be set with the --local-user and --default-key options.

--detach-sign

-b

Make a detached signature.

--encrypt

-e

Encrypt data. This option may be combined with --sign (for a signed and encrypted message), --symmetric (for a message that may be decrypted via a secret key or a passphrase), or --sign and --symmetric together (for a signed message that may be decrypted via a secret key or a passphrase).

--symmetric

-c

Encrypt with a symmetric cipher using a passphrase. The default symmetric cipher used is CAST5, but may be chosen with the --cipher-algo option. This option may be combined with --sign (for a signed and symmetrically encrypted message), --encrypt (for a message that may be decrypted via a secret key or a passphrase), or --sign and --encrypt together (for a signed message that may be decrypted via a secret key or a passphrase).

--store

Store only (make a simple RFC1991 literal data packet).

--decrypt

-d

Decrypt the file given on the command line (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.

--verify

Assume that the first argument is a signed file or a detached 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 aq-aq as the second filename. For security reasons a detached signature cannot read the signed material from STDIN without denoting it in the above way.

--multifile

This modifies certain other commands to accept multiple files for processing on the command line or read from STDIN with each filename on a separate line. This allows for many files to be processed at once. --multifile may currently be used along with --verify, --encrypt, and --decrypt. Note that --multifile --verify may not be used with detached signatures.

--verify-files

Identical to --multifile --verify.

--encrypt-files

Identical to --multifile --encrypt.

--decrypt-files

Identical to --multifile --decrypt.

--list-keys

-k

--list-public-keys

List all keys from the public keyrings, or just the keys given on the command line.

Avoid using the output of this command in scripts or other programs as it is likely to change as GnuPG changes. See --with-colons for a machine-parseable key listing command that is appropriate for use in scripts and other programs.

--list-secret-keys

-K

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).

--list-sigs

Same as --list-keys, but the signatures are listed too. This command has the same effect as using --list-keys with --with-sig-list.

For each signature listed, there are several flags in between the "sig" tag and keyid. These flags give additional information about each signature. From left to right, they are the numbers 1-3 for certificate check level (see --ask-cert-level), "L" for a local or non-exportable signature (see --lsign-key), "R" for a nonRevocable signature (see the --edit-key command "nrsign"), "P" for a signature that contains a policy URL (see --cert-policy-url), "N" for a signature that contains a notation (see --cert-notation), "X" for an eXpired signature (see --ask-cert-expire), and the numbers 1-9 or "T" for 10 and above to indicate trust signature levels (see the --edit-key command "tsign").

--check-sigs

Same as --list-sigs, but the signatures are verified. Note that for performance reasons the revocation status of a signing key is not shown. This command has the same effect as using --list-keys with --with-sig-check.

The status of the verification is indicated by a flag directly following the "sig" tag (and thus before the flags described above for --list-sigs). A "!" indicates that the signature has been successfully verified, a "-" denotes a bad signature and a "%" is used if an error occurred while checking the signature (e.g. a non supported algorithm).

--locate-keys

Locate the keys given as arguments. This command basically uses the same algorithm as used when locating keys for encryption or signing and may thus be used to see what keys gpg2 might use. In particular external methods as defined by --auto-key-locate may be used to locate a key. Only public keys are listed.

--fingerprint

List all keys (or the specified ones) along 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.

--list-packets

List only the sequence of packets. This is mainly useful for debugging.

--card-edit

Present a menu to work with a smartcard. The subcommand "help" provides an overview on available commands. For a detailed description, please see the Card HOWTO at http://www.gnupg.org/documentation/howtos.html#GnuPG-cardHOWTO .

--card-status

Show the content of the smart card.

--change-pin

Present a menu to allow changing the PIN of a smartcard. This functionality is also available as the subcommand "passwd" with the --card-edit command.

--delete-key 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.

--delete-secret-key name

Remove key from the secret and public keyring. In batch mode the key must be specified by fingerprint.

--delete-secret-and-public-key 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.

--export

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.

--send-keys key IDs

Similar to --export but sends the keys to a keyserver. Fingerprints may be used instead of key IDs. 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. If no key IDs are given, gpg does nothing.

--export-secret-keys

--export-secret-subkeys

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.

--import

--fast-import

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 --import-options merge-only option which does not insert new keys but does only the merging of new signatures, user-IDs and subkeys.

--recv-keys 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.

--refresh-keys

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. Calling this with no arguments will refresh the entire keyring. Option --keyserver must be used to give the name of the keyserver for all keys that do not have preferred keyservers set (see --keyserver-options honor-keyserver-url).

--search-keys 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. Keyservers that support different search methods allow using the syntax specified in "How to specify a user ID" below. Note that different keyserver types support different search methods. Currently only LDAP supports them all.

--fetch-keys URIs

Retrieve keys located at the specified URIs. Note that different installations of GnuPG may support different protocols (HTTP, FTP, LDAP, etc.)

--update-trustdb

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

--check-trustdb

Do trust database maintenance without user interaction. From time to time the trust database must be updated so that expired keys or signatures and the resulting changes in the Web of Trust can be tracked. Normally, GnuPG will calculate when this is required and do it automatically unless --no-auto-check-trustdb is set. This command can be used to force a trust database check at any time. The processing is identical 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 trust database check is done only if a check is needed. To force a run even in batch mode add the option --yes.

--export-ownertrust

Send the ownertrust values to STDOUT. This is useful for backup purposes as these values are the only ones which can't be re-created from a corrupted trustdb. Example:

  gpg2 --export-ownertrust > otrust.txt

--import-ownertrust

Update the trustdb with the ownertrust values stored in files (or STDIN if not given); existing values will be overwritten. In case of a severely damaged trustdb and if you have a recent backup of the ownertrust values (e.g. in the file oqotrust.txtcq, you may re-create the trustdb using these commands:

  cd ~/.gnupg
  rm trustdb.gpg
  gpg2 --import-ownertrust < otrust.txt

--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.

--print-md algo

--print-mds

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.

--gen-random 0|1|2

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!

--gen-prime mode bits

Use the source, Luke :-). The output format is still subject to change.

--enarmor

--dearmor

Pack or unpack an arbitrary input into/from an OpenPGP ASCII armor. This is a GnuPG extension to OpenPGP and in general not very useful.

How to manage your keys

This section explains the main commands for key management

--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 oqdoc/DETAILScq in the source distribution on how to use this.

--gen-revoke name

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

--desig-revoke name

Generate a designated revocation certificate for a key. This allows a user (with the permission of the keyholder) to revoke someone else's key.

--edit-key

Present a menu which enables you to do most of the key management related tasks. It expects the specification of a key on the command line.

uid n

Toggle selection of user ID or photographic user ID with index n. Use * to select all and 0 to deselect all.

key n

Toggle selection of subkey with index n. Use * to select all and 0 to deselect all.

sign

Make a signature on key of user 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.

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.

nrsign

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

tsign

Make a trust signature. This is a signature that combines the notions of certification (like a regular signature), and trust (like the "trust" command). It is generally only useful in distinct communities or groups.

Note that "l" (for local / non-exportable), "nr" (for non-revocable, and "t" (for trust) may be freely mixed and prefixed to "sign" to create a signature of any type desired.

delsig

Delete a signature. Note that it is not possible to retract a signature, once it has been send to the public (i.e. to a keyserver). In that case you better use revsig.

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.

check

Check the signatures on all selected user IDs.

adduid

Create an additional user ID.

addphoto

Create a photographic user ID. This will prompt for a JPEG file that will be embedded into the user ID. Note that a very large JPEG will make for a very large key. Also note that some programs will display your JPEG unchanged (GnuPG), and some programs will scale it to fit in a dialog box (PGP).

showphoto

Display the selected photographic user ID.

deluid

Delete a user ID or photographic user ID. Note that it is not possible to retract a user id, once it has been send to the public (i.e. to a keyserver). In that case you better use revuid.

revuid

Revoke a user ID or photographic user ID.

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.

keyserver

Set a preferred keyserver for the specified user ID(s). This allows other users to know where you prefer they get your key from. See --keyserver-options honor-keyserver-url for more on how this works. Setting a value of "none" removes an existing preferred keyserver.

notation

Set a name=value notation for the specified user ID(s). See --cert-notation for more on how this works. Setting a value of "none" removes all notations, setting a notation prefixed with a minus sign (-) removes that notation, and setting a notation name (without the =value) prefixed with a minus sign removes all notations with that name.

pref

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

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. In addition, the preferred keyserver and signature notations (if any) are shown.

setpref string

Set the list of user ID preferences to string for all (or just the selected) user IDs. Calling setpref with no arguments sets the preference list to the default (either built-in or set via --default-preference-list), and calling setpref with "none" as the argument sets an empty preference list. Use gpg2 --version to get a list of available algorithms. 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.

When setting preferences, you should list the algorithms in the order which you'd like to see them used by someone else when encrypting a message to your key. If you don't include 3DES, it will be automatically added at the end. Note that there are many factors that go into choosing an algorithm (for example, your key may not be the only recipient), and so the remote OpenPGP application being used to send to you may or may not follow your exact chosen order for a given message. It will, however, only choose an algorithm that is present on the preference list of every recipient key. See also the INTEROPERABILITY WITH OTHER OPENPGP PROGRAMS section below.

addkey

Add a subkey to this key.

addcardkey

Generate a subkey on a card and add it to this key.

keytocard

Transfer the selected secret subkey (or the primary key if no subkey has been selected) to a smartcard. The secret key in the keyring will be replaced by a stub if the key could be stored successfully on the card and you use the save command later. Only certain key types may be transferred to the card. A sub menu allows you to select on what card to store the key. Note that it is not possible to get that key back from the card - if the card gets broken your secret key will be lost unless you have a backup somewhere.

bkuptocard file

Restore the given file to a card. This command may be used to restore a backup key (as generated during card initialization) to a new card. In almost all cases this will be the encryption key. You should use this command only with the corresponding public key and make sure that the file given as argument is indeed the backup to restore. You should then select 2 to restore as encryption key. You will first be asked to enter the passphrase of the backup key and then for the Admin PIN of the card.

delkey

Remove a subkey (secondart key). Note that it is not possible to retract a subkey, once it has been send to the public (i.e. to a keyserver). In that case you better use revkey.

revkey

Revoke a subkey.

expire

Change the key or subkey 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.

trust

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

disable

enable

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

addrevoker

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

passwd

Change the passphrase of the secret key.

toggle

Toggle between public and secret key listing.

clean

Compact (by removing all signatures except the selfsig) any user ID that is no longer usable (e.g. revoked, or expired). Then, remove any signatures that are not usable by the trust calculations. Specifically, this removes any signature that does not validate, any signature that is superseded by a later signature, revoked signatures, and signatures issued by keys that are not present on the keyring.

minimize

Make the key as small as possible. This removes all signatures from each user ID except for the most recent self-signature.

cross-certify

Add cross-certification signatures to signing subkeys that may not currently have them. Cross-certification signatures protect against a subtle attack against signing subkeys. See --require-cross-certification. All new keys generated have this signature by default, so this option is only useful to bring older keys up to date.

save

Save all changes to the key rings and quit.

quit

Quit the program without updating the key rings.

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:

-

No ownertrust assigned / not yet calculated.

e

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

q

Not enough information for calculation.

n

Never trust this key.

m

Marginally trusted.

f

Fully trusted.

u

Ultimately trusted.

--sign-key name

Signs a public key with your secret key. This is a shortcut version of the subcommand "sign" from --edit.

--lsign-key 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-key.

OPTIONS

gpg2 comes features a bunch of options to control the exact behaviour and to change the default configuration.

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 is not generally useful as the command will execute automatically with every execution of gpg.

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

How to change the configuration

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

--default-key name

Use name as the default key to sign with. If this option is not used, the default key is the first key found in the secret keyring. Note that -u or --local-user overrides this option.

--default-recipient name

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

--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.

--no-default-recipient

Reset --default-recipient and --default-recipient-self.

-v, --verbose

Give more information during processing. If used twice, the input data is listed in detail.

--no-verbose

Reset verbose level to 0.

-q, --quiet

Try to be as quiet as possible.

--batch

--no-batch

Use batch mode. Never ask, do not allow interactive commands. --no-batch disables this option. Note that even with a filename given on the command line, gpg might still need to read from STDIN (in particular if gpg figures that the input is a detached signature and no data file has been specified). Thus if you do not want to feed data via STDIN, you should connect STDIN to oq/dev/nullcq.

--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 even if --batch is used.

--yes

Assume "yes" on most questions.

--no

Assume "no" on most questions.

--list-options parameters

This is a space or comma delimited string that gives options used when listing keys and signatures (that is, --list-keys, --list-sigs, --list-public-keys, --list-secret-keys, and the --edit-key functions). Options can be prepended with a no- (after the two dashes) to give the opposite meaning. The options are:

show-photos

Causes --list-keys, --list-sigs, --list-public-keys, and --list-secret-keys to display any photo IDs attached to the key. Defaults to no. See also --photo-viewer.

show-policy-urls

Show policy URLs in the --list-sigs or --check-sigs listings. Defaults to no.

show-notations

show-std-notations

show-user-notations

Show all, IETF standard, or user-defined signature notations in the --list-sigs or --check-sigs listings. Defaults to no.

show-keyserver-urls

Show any preferred keyserver URL in the --list-sigs or --check-sigs listings. Defaults to no.

show-uid-validity

Display the calculated validity of user IDs during key listings. Defaults to no.

show-unusable-uids

Show revoked and expired user IDs in key listings. Defaults to no.

show-unusable-subkeys

Show revoked and expired subkeys in key listings. Defaults to no.

show-keyring

Display the keyring name at the head of key listings to show which keyring a given key resides on. Defaults to no.

show-sig-expire

Show signature expiration dates (if any) during --list-sigs or --check-sigs listings. Defaults to no.

show-sig-subpackets

Include signature subpackets in the key listing. This option can take an optional argument list of the subpackets to list. If no argument is passed, list all subpackets. Defaults to no. This option is only meaningful when using --with-colons along with --list-sigs or --check-sigs.

--verify-options parameters

This is a space or comma delimited string that gives options used when verifying signatures. Options can be prepended with a `no-' to give the opposite meaning. The options are:

show-photos

Display any photo IDs present on the key that issued the signature. Defaults to no. See also --photo-viewer.

show-policy-urls

Show policy URLs in the signature being verified. Defaults to no.

show-notations

show-std-notations

show-user-notations

Show all, IETF standard, or user-defined signature notations in the signature being verified. Defaults to IETF standard.

show-keyserver-urls

Show any preferred keyserver URL in the signature being verified. Defaults to no.

show-uid-validity

Display the calculated validity of the user IDs on the key that issued the signature. Defaults to no.

show-unusable-uids

Show revoked and expired user IDs during signature verification. Defaults to no.

show-primary-uid-only

Show only the primary user ID during signature verification. That is all the AKA lines as well as photo Ids are not shown with the signature verification status.

pka-lookups

Enable PKA lookups to verify sender addresses. Note that PKA is based on DNS, and so enabling this option may disclose information on when and what signatures are verified or to whom data is encrypted. This is similar to the "web bug" described for the auto-key-retrieve feature.

pka-trust-increase

Raise the trust in a signature to full if the signature passes PKA validation. This option is only meaningful if pka-lookups is set.

--enable-dsa2

--disable-dsa2

Enable hash truncation for all DSA keys even for old DSA Keys up to 1024 bit. This is also the default with --openpgp. Note that older versions of GnuPG also required this flag to allow the generation of DSA larger than 1024 bit.

--photo-viewer 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". Note that if your image viewer program is not secure, then executing it from GnuPG does not make it secure.

--exec-path 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. Note, that on W32 system this value is ignored when searching for keyserver helpers.

--keyring file

Add file to the current list of keyrings. If 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 GnuPG home directory ("~/.gnupg" if --homedir or $GNUPGHOME is not used).

Note that this adds a keyring to the current list. If the intent is to use the specified keyring alone, use --keyring along with --no-default-keyring.

--secret-keyring file

Same as --keyring but for the secret keyrings.

--primary-keyring file

Designate file as the primary public keyring. This means that newly imported keys (via --import or keyserver --recv-from) will go to this keyring.

--trustdb-name file

Use file instead of the default trustdb. If 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 GnuPG home directory (oq~/.gnupgcq if --homedir or $GNUPGHOME is not used).

--homedir dir

Set the name of the home directory to dir. If this option is not used, the home directory defaults to oq~/.gnupgcq. It is only recognized when given on the command line. It also overrides any home directory stated through the environment variable oqGNUPGHOMEcq or (on W32 systems) by means of the Registry entry HKCU\Software\GNU\GnuPG:HomeDir.

--display-charset name

Set the name of the native character set. This is used to convert some informational strings like user IDs to the proper UTF-8 encoding. Note that this has nothing to do with the character set of data to be encrypted or signed; GnuPG does not recode user-supplied data. If this option is not used, the default character set is determined from the current locale. A verbosity level of 3 shows the chosen set. Valid values for name are:

iso-8859-1

This is the Latin 1 set.

iso-8859-2

The Latin 2 set.

iso-8859-15

This is currently an alias for the Latin 1 set.

koi8-r

The usual Russian set (rfc1489).

utf-8

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

--utf8-strings

--no-utf8-strings

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

--options file

Read options from 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.

--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 oq~/.gnupgcq homedir.

-z n

--compress-level n

--bzip2-compress-level n

Set compression level to n for the ZIP and ZLIB compression algorithms. The default is to use the default compression level of zlib (normally 6). --bzip2-compress-level sets the compression level for the BZIP2 compression algorithm (defaulting to 6 as well). This is a different option from --compress-level since BZIP2 uses a significant amount of memory for each additional compression level. -z sets both. A value of 0 for n disables compression.

--bzip2-decompress-lowmem

Use a different decompression method for BZIP2 compressed files. This alternate method uses a bit more than half the memory, but also runs at half the speed. This is useful under extreme low memory circumstances when the file was originally compressed at a high --bzip2-compress-level.

--mangle-dos-filenames

--no-mangle-dos-filenames

Older version of Windows cannot handle filenames with more than one dot. --mangle-dos-filenames causes GnuPG to replace (rather than add to) the extension of an output filename to avoid this problem. This option is off by default and has no effect on non-Windows platforms.

--ask-cert-level

--no-ask-cert-level

When making a key signature, prompt for a certification level. If this option is not specified, the certification level used is set via --default-cert-level. See --default-cert-level for information on the specific levels and how they are used. --no-ask-cert-level disables this option. This option defaults to no.

--default-cert-level 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 (no particular claim).

--min-cert-level

When building the trust database, treat any signatures with a certification level below this as invalid. Defaults to 2, which disregards level 1 signatures. Note that level 0 "no particular claim" signatures are always accepted.

--trusted-key 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.

--trust-model pgp|classic|direct|always|auto

Set what trust model GnuPG should follow. The models are:

pgp

This is the Web of Trust combined with trust signatures as used in PGP 5.x and later. This is the default trust model when creating a new trust database.

classic

This is the standard Web of Trust as used in PGP 2.x and earlier.

direct

Key validity is set directly by the user and not calculated via the Web of Trust.

always

Skip key validation and assume that used keys are always fully trusted. You generally won't use this unless you are using 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.

auto

Select the trust model depending on whatever the internal trust database says. This is the default model if such a database already exists.

--auto-key-locate parameters

--no-auto-key-locate

GnuPG can automatically locate and retrieve keys as needed using this option. This happens when encrypting to an email address (in the "user@example.com" form), and there are no user@example.com keys on the local keyring. This option takes any number of the following mechanisms, in the order they are to be tried:

cert

Locate a key using DNS CERT, as specified in rfc4398.

pka

Locate a key using DNS PKA.

ldap

Using DNS Service Discovery, check the domain in question for any LDAP keyservers to use. If this fails, attempt to locate the key using the PGP Universal method of checking aqldap://keys.(thedomain)aq.

keyserver

Locate a key using whatever keyserver is defined using the --keyserver option.

keyserver-URL

In addition, a keyserver URL as used in the --keyserver option may be used here to query that particular keyserver.

local

Locate the key using the local keyrings. This mechanism allows to select the order a local key lookup is done. Thus using aq--auto-key-locate localaq is identical to --no-auto-key-locate.

nodefault

This flag disables the standard local key lookup, done before any of the mechanisms defined by the --auto-key-locate are tried. The position of this mechanism in the list does not matter. It is not required if local is also used.

--keyid-format short|0xshort|long|0xlong

Select how to display key IDs. "short" is the traditional 8-character key ID. "long" is the more accurate (but less convenient) 16-character key ID. Add an "0x" to either to include an "0x" at the beginning of the key ID, as in 0x99242560.

--keyserver name

Use 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 name is a URI: `scheme:[//]keyservername[:port]' The scheme is the type of keyserver: "hkp" for the HTTP (or compatible) keyservers, "ldap" for the LDAP keyservers, or "mailto" for the Graff email keyserver. Note that your particular installation of GnuPG may have other keyserver types available as well. Keyserver schemes are case-insensitive. After the keyserver name, optional keyserver configuration options may be provided. These are the same as the global --keyserver-options from below, but apply only to this particular keyserver.

Most keyservers synchronize with each other, so there is generally no need to send keys to more than one server. The keyserver hkp://keys.gnupg.net uses round robin DNS to give a different keyserver each time you use it.

--keyserver-options name=value1

This is a space or comma delimited string that gives options for the keyserver. Options can be prefixed 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:

include-revoked

When searching for a key with --search-keys, include keys that are marked on the keyserver as revoked. Note that not all keyservers differentiate between revoked and unrevoked keys, and for such keyservers this option is meaningless. Note also that most keyservers do not have cryptographic verification of key revocations, and so turning this option off may result in skipping keys that are incorrectly marked as revoked.

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.

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.

Note that this option makes a "web bug" like behavior possible. Keyserver 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 keyring), the operator can tell both your IP address and the time when you verified the signature.

honor-keyserver-url

When using --refresh-keys, if the key in question has a preferred keyserver URL, then use that preferred keyserver to refresh the key from. In addition, if auto-key-retrieve is set, and the signature being verified has a preferred keyserver URL, then use that preferred keyserver to fetch the key from. Defaults to yes.

honor-pka-record

If auto-key-retrieve is set, and the signature being verified has a PKA record, then use the PKA information to fetch the key. Defaults to yes.

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.

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.

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.

verbose

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

timeout

Tell the keyserver helper program how long (in seconds) to try and perform a keyserver action before giving up. Note that performing multiple actions at the same time uses this timeout value per action. For example, when retrieving multiple keys via --recv-keys, the timeout applies separately to each key retrieval, and not to the --recv-keys command as a whole. Defaults to 30 seconds.

http-proxy=value

Set the proxy to use for HTTP and HKP keyservers. This overrides the "http_proxy" environment variable, if any.

max-cert-size

When retrieving a key via DNS CERT, only accept keys up to this size. Defaults to 16384 bytes.

debug

Turn on debug output in the keyserver helper program. Note that the details of debug output depends on which keyserver helper program is being used, and in turn, on any libraries that the keyserver helper program uses internally (libcurl, openldap, etc).

check-cert

Enable certificate checking if the keyserver presents one (for hkps or ldaps). Defaults to on.

ca-cert-file

Provide a certificate file to override the system default. Only necessary if check-cert is enabled, and the keyserver is using a certificate that is not present in a system default certificate list.

--completes-needed n

Number of completely trusted users to introduce a new key signer (defaults to 1).

--marginals-needed n

Number of marginally trusted users to introduce a new key signer (defaults to 3)

--max-cert-depth n

Maximum depth of a certification chain (default is 5).

--simple-sk-checksum

Secret keys are integrity protected by using a SHA-1 checksum. This method is part of the upcoming 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 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).

--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.

--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.

--auto-check-trustdb

--no-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. --no-auto-check-trustdb disables this option.

--use-agent

--no-use-agent

This is dummy option. gpg2 always requires the agent.

--gpg-agent-info

This is dummy option. It has no effect when used with gpg2.

--lock-once

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

--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.

--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.

--exit-on-status-write-error

This option will cause write errors on the status FD to immediately terminate the process. That should in fact be the default but it never worked this way and thus we need an option to enable this, so that the change won't break applications which close their end of a status fd connected pipe too early. Using this option along with --enable-progress-filter may be used to cleanly cancel long running gpg operations.

--limit-card-insert-tries n

With n greater than 0 the number of prompts asking to insert a smartcard gets limited to N-1. Thus with a value of 1 gpg won't at all ask to insert a card if none has been inserted at startup. This option is useful in the configuration file in case an application does not know about the smartcard support and waits ad infinitum for an inserted card.

--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.

--no-greeting

Suppress the initial copyright message.

--no-secmem-warning

Suppress the warning about "using insecure memory".

--no-permission-warning

Suppress the warning about unsafe file and home directory (--homedir) permissions. Note that the permission checks that GnuPG performs are not intended to be authoritative, but rather they simply warn about certain common permission problems. Do not assume that the lack of a warning means that your system is secure.

Note that the warning for unsafe --homedir permissions cannot be suppressed in the gpg.conf file, as this would allow an attacker to place an unsafe gpg.conf file in place, and use this file to suppress warnings about itself. The --homedir permissions warning may only be suppressed on the command line.

--no-mdc-warning

Suppress the warning about missing MDC integrity protection.

--require-secmem

--no-require-secmem

Refuse to run if GnuPG cannot get secure memory. Defaults to no (i.e. run, but give a warning).

--require-cross-certification

--no-require-cross-certification

When verifying a signature made from a subkey, ensure that the cross certification "back signature" on the subkey is present and valid. This protects against a subtle attack against subkeys that can sign. Defaults to --require-cross-certification for gpg2.

--expert

--no-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 unusual 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. --no-expert disables this option.

Key related options

--recipient name

-r

Encrypt for user id name. If this option or --hidden-recipient is not specified, GnuPG asks for the user-id unless --default-recipient is given.

--hidden-recipient name

-R

Encrypt for user ID name, but hide the key ID of this user's key. This option helps to hide the receiver of the message and is a limited countermeasure against traffic analysis. If this option or --recipient is not specified, GnuPG asks for the user ID unless --default-recipient is given.

--encrypt-to 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.

--hidden-encrypt-to name

Same as --hidden-recipient but this one is intended for use in the options file and may be used with your own user-id as a hidden "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.

--no-encrypt-to

Disable the use of all --encrypt-to and --hidden-encrypt-to keys.

--group name=value1

Sets up a named group, which is similar to aliases in email programs. Any time the group name is a recipient (-r or --recipient), it will be expanded to the values specified. Multiple groups with the same name are automatically merged into a single group.

The values are 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.

--ungroup name

Remove a given entry from the --group list.

--no-groups

Remove all entries from the --group list.

--local-user name

-u

Use name as the key to sign with. Note that this option overrides --default-key.

--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-keyids) and might come handy in case where an encrypted message contains a bogus key ID.

Input and Output

--armor

-a

Create ASCII armored output. The default is to create the binary OpenPGP format.

--no-armor

Assume the input data is not in ASCII armored format.

--output file

-o file

Write output to file.

--max-output n

This option sets a limit on the number of bytes that will be generated when processing a file. Since OpenPGP supports various levels of compression, it is possible that the plaintext of a given message may be significantly larger than the original OpenPGP message. While GnuPG works properly with such messages, there is often a desire to set a maximum file size that will be generated before processing is forced to stop by the OS limits. Defaults to 0, which means "no limit".

--import-options 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:

import-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.

repair-pks-subkey-bug

During import, attempt to repair the damage caused by the PKS keyserver bug (pre version 0.9.6) that mangles keys with multiple subkeys. 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.

merge-only

During import, allow key updates to existing keys, but do not allow any new keys to be imported. Defaults to no.

import-clean

After import, compact (remove all signatures except the self-signature) any user IDs from the new key that are not usable. Then, remove any signatures from the new key that are not usable. This includes signatures that were issued by keys that are not present on the keyring. This option is the same as running the --edit-key command "clean" after import. Defaults to no.

import-minimal

Import the smallest key possible. This removes all signatures except the most recent self-signature on each user ID. This option is the same as running the --edit-key command "minimize" after import. Defaults to no.

--export-options 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:

export-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.

export-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.

export-sensitive-revkeys

Include designated revoker information that was marked as "sensitive". Defaults to no.

export-reset-subkey-passwd

When using the --export-secret-subkeys command, this option resets the passphrases for all exported subkeys to empty. This is useful when the exported subkey is to be used on an unattended machine where a passphrase doesn't necessarily make sense. Defaults to no.

export-clean

Compact (remove all signatures from) user IDs on the key being exported if the user IDs are not usable. Also, do not export any signatures that are not usable. This includes signatures that were issued by keys that are not present on the keyring. This option is the same as running the --edit-key command "clean" before export except that the local copy of the key is not modified. Defaults to no.

export-minimal

Export the smallest key possible. This removes all signatures except the most recent self-signature on each user ID. This option is the same as running the --edit-key command "minimize" before export except that the local copy of the key is not modified. Defaults to no.

--with-colons

Print key listings delimited by colons. Note that the output will be encoded in UTF-8 regardless of any --display-charset setting. This format is useful when GnuPG is called from scripts and other programs as it is easily machine parsed. The details of this format are documented in the file oqdoc/DETAILScq, which is included in the GnuPG source distribution.

--fixed-list-mode

Do not merge primary user ID and primary key in --with-colon listing mode and print all timestamps as seconds since 1970-01-01. Since GnuPG 2.0.10, this mode is always used and thus this option is obsolete; it does not harm to use it though.

--with-fingerprint

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

OpenPGP protocol specific options.

-t, --textmode

--no-textmode

Treat input files as text and store them in the OpenPGP canonical text form with standard "CRLF" line endings. This also sets the necessary flags to inform the recipient that the encrypted or signed data is text and may need its line endings converted back to whatever the local system uses. This option is useful when communicating between two platforms that have different line ending conventions (UNIX-like to Mac, Mac to Windows, etc). --no-textmode disables this option, and is the default.

--force-v3-sigs

--no-force-v3-sigs

OpenPGP states that an implementation should generate v4 signatures but PGP versions 5 through 7 only recognize v4 signatures on key material. This option forces v3 signatures for signatures on data. Note that this option implies --ask-sig-expire, --sig-policy-url, --sig-notation, and --sig-keyserver-url, as these features cannot be used with v3 signatures. --no-force-v3-sigs disables this option.

--force-v4-certs

--no-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. --no-force-v4-certs disables this option.

--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 all of the recipient keys indicate MDC support in their feature flags.

--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.

--personal-cipher-preferences string

Set the list of personal cipher preferences to string. Use gpg2 --version to get a list of available algorithms, and use none to set no preference at all. This allows the user to safely override the algorithm chosen by the recipient key preferences, as GPG will only select an algorithm that is usable by all recipients. The most highly ranked cipher in this list is also used for the --symmetric encryption command.

--personal-digest-preferences string

Set the list of personal digest preferences to string. Use gpg2 --version to get a list of available algorithms, and use none to set no preference at all. This allows the user to safely override the algorithm chosen by the recipient key preferences, as GPG will only select an algorithm that is usable by all recipients. The most highly ranked digest algorithm in this list is also used when signing without encryption (e.g. --clearsign or --sign). The default value is SHA-1.

--personal-compress-preferences string

Set the list of personal compression preferences to string. Use gpg2 --version to get a list of available algorithms, and use none to set no preference at all. This allows the user to safely override the algorithm chosen by the recipient key preferences, as GPG will only select an algorithm that is usable by all recipients. The most highly ranked compression algorithm in this list is also used when there are no recipient keys to consider (e.g. --symmetric).

--s2k-cipher-algo name

Use name as the cipher algorithm used to protect secret keys. The default cipher is CAST5. This cipher is also used for conventional encryption if --personal-cipher-preferences and --cipher-algo is not given.

--s2k-digest-algo name

Use name as the digest algorithm used to mangle the passphrases. The default algorithm is SHA-1.

--s2k-mode n

Selects how passphrases are mangled. If 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 number of times (see --s2k-count). Unless --rfc1991 is used, this mode is also used for conventional encryption.

--s2k-count n

Specify how many times the passphrase mangling is repeated. This value may range between 1024 and 65011712 inclusive, and the default is 65536. Note that not all values in the 1024-65011712 range are legal and if an illegal value is selected, GnuPG will round up to the nearest legal value. This option is only meaningful if --s2k-mode is 3.

Compliance options

These options control what GnuPG is compliant to. Only one of these options may be active at a time. Note that the default setting of this is nearly always the correct one. See the INTEROPERABILITY WITH OTHER OPENPGP PROGRAMS section below before using one of these options.

--gnupg

Use standard GnuPG behavior. This is essentially OpenPGP behavior (see --openpgp), but with some additional workarounds for common compatibility problems in different versions of PGP. This is the default option, so it is not generally needed, but it may be useful to override a different compliance option in the gpg.conf file.

--openpgp

Reset all packet, cipher and digest options to strict OpenPGP behavior. Use this option to reset all previous options like --s2k-*, --cipher-algo, --digest-algo and --compress-algo to OpenPGP compliant values. All PGP workarounds are disabled.

--rfc4880

Reset all packet, cipher and digest options to strict RFC-4880 behavior. Note that this is currently the same thing as --openpgp.

--rfc2440

Reset all packet, cipher and digest options to strict RFC-2440 behavior.

--rfc1991

Try to be more RFC-1991 (PGP 2.x) compliant.

--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 --disable-mdc --no-force-v4-certs --escape-from-lines --force-v3-sigs --cipher-algo IDEA --digest-algo MD5 --compress-algo ZIP. It also disables --textmode when encrypting.

--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-keyids, and making signatures with signing subkeys as PGP 6 does not understand signatures made by signing subkeys.

This option implies --disable-mdc --escape-from-lines --force-v3-sigs.

--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.

--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-keyids and set --escape-from-lines. All algorithms are allowed except for the SHA224, SHA384, and SHA512 digests.

Doing things one usually doesn't want to do.

-n

--dry-run

Don't make any changes (this is not completely implemented).

--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.

-i

--interactive

Prompt before overwriting any files.

--debug flags

Set debugging flags. All flags are or-ed and flags may be given in C syntax (e.g. 0x0042).

--debug-all

Set all useful debugging flags.

--enable-progress-filter

Enable certain PROGRESS status outputs. This option allows frontends to display a progress indicator while gpg is processing larger files. There is a slight performance overhead using it.

--status-fd n

Write special status strings to the file descriptor n. See the file DETAILS in the documentation for a listing of them.

--status-file file

Same as --status-fd, except the status data is written to file file.

--logger-fd n

Write log output to file descriptor n and not to STDERR.

--log-file file

--logger-file file

Same as --logger-fd, except the logger data is written to file file. Note that --log-file is only implemented for GnuPG-2.

--attribute-fd n

Write attribute subpackets to the file descriptor 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.

--attribute-file file

Same as --attribute-fd, except the attribute data is written to file file.

--comment string

--no-comments

Use string as a comment string in clear text signatures and ASCII armored messages or keys (see --armor). The default behavior is not to use a comment string. --comment may be repeated multiple times to get multiple comment strings. --no-comments removes all comments. It is a good idea to keep the length of a single comment below 60 characters to avoid problems with mail programs wrapping such lines. Note that comment lines, like all other header lines, are not protected by the signature.

--emit-version

--no-emit-version

Force inclusion of the version string in ASCII armored output. --no-emit-version disables this option.

--sig-notation name=value

--cert-notation name=value

-N, --set-notation name=value

Put the name value pair into the signature as notation data. name must consist only of printable characters or spaces, and must contain a '@' character in the form keyname@domain.example.com (substituting the appropriate keyname and domain name, of course). This is to help prevent pollution of the IETF reserved notation namespace. The --expert flag overrides the '@' check. value may be any printable string; it will be encoded in UTF8, so you should check that your --display-charset is set correctly. If you prefix 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). --set-notation 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" into the long key ID of the key being signed, "%f" into the fingerprint of the key being signed, "%s" into the key ID of the key making the signature, "%S" into the long key ID of the key making the signature, "%g" into the fingerprint of the key making the signature (which might be a subkey), "%p" into the fingerprint of the primary key of the key making the signature, "%c" into the signature count from the OpenPGP smartcard, and "%%" results in a single "%". %k, %K, and %f are only meaningful when making a key signature (certification), and %c is only meaningful when using the OpenPGP smartcard.

--sig-policy-url string

--cert-policy-url string

--set-policy-url string

Use string as a 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 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.

--sig-keyserver-url string

Use string as a preferred keyserver URL for data signatures. If you prefix it with an exclamation mark (!), the keyserver URL packet will be flagged as critical.

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

--set-filename string

Use string as the filename which is stored inside messages. This overrides the default, which is to use the actual filename of the file being encrypted.

--for-your-eyes-only

--no-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 a "secure viewer" with a claimed Tempest-resistant font to display the message. This option overrides --set-filename. --no-for-your-eyes-only disables this option.

--use-embedded-filename

--no-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. Defaults to no.

--cipher-algo name

Use 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. In general, you do not want to use this option as it allows you to violate the OpenPGP standard. --personal-cipher-preferences is the safe way to accomplish the same thing.

--digest-algo name

Use name as the message digest algorithm. Running the program with the command --version yields a list of supported algorithms. In general, you do not want to use this option as it allows you to violate the OpenPGP standard. --personal-digest-preferences is the safe way to accomplish the same thing.

--compress-algo name

Use compression algorithm name. "zlib" is RFC-1950 ZLIB compression. "zip" is RFC-1951 ZIP compression which is used by PGP. "bzip2" is a more modern compression scheme that can compress some things better than zip or zlib, but at the cost of more memory used during compression and decompression. "uncompressed" or "none" 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.

ZLIB may give better compression results than ZIP, as the compression window size is not limited to 8k. BZIP2 may give even better compression results than that, but will use a significantly larger amount of memory while compressing and decompressing. This may be significant in low memory situations. Note, however, that PGP (all versions) only supports ZIP compression. Using any algorithm other than ZIP or "none" will make the message unreadable with PGP. In general, you do not want to use this option as it allows you to violate the OpenPGP standard. --personal-compress-preferences is the safe way to accomplish the same thing.

--cert-digest-algo name

Use 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.

--disable-cipher-algo name

Never allow the use of name as cipher algorithm. The given name will not be checked so that a later loaded algorithm will still get disabled.

--disable-pubkey-algo name

Never allow the use of name as public key algorithm. The given name will not be checked so that a later loaded algorithm will still get disabled.

--throw-keyids

--no-throw-keyids

Do not put the recipient key IDs into encrypted messages. This helps to hide the receivers of the message and is a limited countermeasure against traffic analysis. ([Using a little social engineering anyone who is able to decrypt the message can check whether one of the other recipients is the one he suspects.]) On the receiving side, it may slow down the decryption process because all available secret keys must be tried. --no-throw-keyids disables this option. This option is essentially the same as using --hidden-recipient for all recipients.

--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.

--escape-from-lines

--no-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 to prevent the mail system from breaking the signature. Note that all other PGP versions do it this way too. Enabled by default. --no-escape-from-lines disables this option.

--passphrase-repeat n

Specify how many times gpg2 will request a new passphrase be repeated. This is useful for helping memorize a passphrase. Defaults to 1 repetition.

--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. This is different from gpg.

--passphrase-file file

Read the passphrase from file file. Only the first line will be read from file file. This can only be used if only one passphrase is supplied. Obviously, a passphrase stored in a file is of questionable security if other users can read this file. Don't use this option if you can avoid it. Note that this passphrase is only used if the option --batch has also been given. This is different from gpg.

--passphrase string

Use string as the passphrase. This can only be used if only one passphrase is supplied. Obviously, this is of very questionable security on a multi-user system. Don't use this option if you can avoid it. Note that this passphrase is only used if the option --batch has also been given. This is different from gpg.

--command-fd 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.

--command-file file

Same as --command-fd, except the commands are read out of file file

--allow-non-selfsigned-uid

--no-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. --no-allow-non-selfsigned-uid disables.

--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.

--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. See also --ignore-valid-from for timestamp issues on subkeys.

--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. See also --ignore-time-conflict for timestamp issues with signatures.

--ignore-crc-error

The ASCII armor used by OpenPGP is protected by a CRC checksum against transmission errors. Occasionally 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 allows GnuPG to ignore CRC errors.

--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.

--no-default-keyring

Do not add the default keyrings to the list of keyrings. Note that GnuPG will not operate without any keyrings, so if you use this option and do not provide alternate keyrings via --keyring or --secret-keyring, then GnuPG will still use the default public or secret keyrings.

--skip-verify

Skip the signature verification step. This may be used to make the decryption faster if the signature verification is not needed.

--with-key-data

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

--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. If you are missing some information, don't use this option.

--no-literal

This is not for normal use. Use the source to see for what it might be useful.

--set-filesize

This is not for normal use. Use the source to see for what it might be useful.

--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.

--override-session-key string

Don't use the public key but the session key 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.

--ask-sig-expire

--no-ask-sig-expire

When making a data signature, prompt for an expiration time. If this option is not specified, the expiration time set via --default-sig-expire is used. --no-ask-sig-expire disables this option. Note that by default, --force-v3-sigs is set which also disables this option. If you want signature expiration, you must set --no-force-v3-sigs as well as turning --ask-sig-expire on.

--default-sig-expire

The default expiration time to use for signature expiration. Valid values are "0" for no expiration, a number followed by the letter d (for days), w (for weeks), m (for months), or y (for years) (for example "2m" for two months, or "5y" for five years), or an absolute date in the form YYYY-MM-DD. Defaults to "0".

--ask-cert-expire

--no-ask-cert-expire

When making a key signature, prompt for an expiration time. If this option is not specified, the expiration time set via --default-cert-expire is used. --no-ask-cert-expire disables this option.

--default-cert-expire

The default expiration time to use for key signature expiration. Valid values are "0" for no expiration, a number followed by the letter d (for days), w (for weeks), m (for months), or y (for years) (for example "2m" for two months, or "5y" for five years), or an absolute date in the form YYYY-MM-DD. Defaults to "0".

--allow-secret-key-import

This is an obsolete option and is not used anywhere.

--allow-multiple-messages

--no-allow-multiple-messages

Allow processing of multiple OpenPGP messages contained in a single file or stream. Some programs that call GPG are not prepared to deal with multiple messages being processed together, so this option defaults to no. Note that versions of GPG prior to 1.4.7 always allowed multiple messages.

Warning: Do not use this option unless you need it as a temporary workaround!

--enable-special-filenames

This options enables a mode in which filenames of the form oq-&ncq, where n is a non-negative decimal number, refer to the file descriptor n and not to a file with that name.

--no-expensive-trust-checks

Experimental use only.

--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.

--default-preference-list string

Set the list of default preferences to string. This preference list is used for new keys and becomes the default for "setpref" in the edit menu.

--default-keyserver-url name

Set the default keyserver URL to name. This keyserver will be used as the keyserver URL when writing a new self-signature on a key, which includes key generation and changing preferences.

--list-config

Display various internal configuration parameters of GnuPG. This option is intended for external programs that call GnuPG to perform tasks, and is thus not generally useful. See the file oqdoc/DETAILScq in the source distribution for the details of which configuration items may be listed. --list-config is only usable with --with-colons set.

--gpgconf-list

This command is similar to --list-config but in general only internally used by the gpgconf tool.

--gpgconf-test

This is more or less dummy action. However it parses the configuration file and returns with failure if the configuration file would prevent gpg from startup. Thus it may be used to run a syntax check on the configuration file.

Deprecated options

--show-photos

--no-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. These options are deprecated. Use --list-options [no-]show-photos and/or --verify-options [no-]show-photos instead.

--show-keyring

Display the keyring name at the head of key listings to show which keyring a given key resides on. This option is deprecated: use --list-options [no-]show-keyring instead.

--always-trust

Identical to --trust-model always. This option is deprecated.

--show-notation

--no-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. These options are deprecated. Use --list-options [no-]show-notation and/or --verify-options [no-]show-notation instead.

--show-policy-url

--no-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. These options are deprecated. Use --list-options [no-]show-policy-url and/or --verify-options [no-]show-policy-url instead.

EXAMPLES

gpg -se -r Bob file

sign and encrypt for user Bob

gpg --clearsign file

make a clear text signature

gpg -sb file

make a detached signature

gpg -u 0x12345678 -sb file

make a detached signature with the key 0x12345678

gpg --list-keys user_ID

show keys

gpg --fingerprint user_ID

show fingerprint

gpg --verify pgpfile

gpg --verify sigfile

Verify the signature of the file but do not output the data. The second form is used for detached signatures, where sigfile is the detached signature (either ASCII armored or binary) and 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 sigfile or by asking the user for the filename.

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.)

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 word match.

All words must match exactly (not case sensitive) but can appear in any order in the user ID or a subjects name. Words are any sequences of letters, digits, the underscore and all characters with bit 7 set.

+Heinrich Heine duesseldorf

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 as 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 rfc2253 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

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.

FILES

There are a few configuration files to control certain aspects of gpg2's operation. Unless noted, they are expected in the current home directory (see: [option --homedir]).

gpg.conf

This is the standard configuration file read by gpg2 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: [option --options]). You should backup this file.

Note that on larger installations, it is useful to put predefined files into the directory oq/etc/skel/.gnupg/cq so that newly created users start up with a working configuration. For existing users the a small helper script is provided to create these files (see: [addgnupghome]).

For internal purposes gpg2 creates and maintains a few other files; They all live in in the current home directory (see: [option --homedir]). Only the gpg2 may modify these files.

~/.gnupg/secring.gpg

The secret keyring. You should backup this file.

~/.gnupg/secring.gpg.lock

The lock file for the secret keyring.

~/.gnupg/pubring.gpg

The public keyring. You should backup this file.

~/.gnupg/pubring.gpg.lock

The lock file for the public keyring.

~/.gnupg/trustdb.gpg

The trust database. There is no need to backup this file; it is better to backup the ownertrust values (see: [option --export-ownertrust]).

~/.gnupg/trustdb.gpg.lock

The lock file for the trust database.

~/.gnupg/random_seed

A file used to preserve the state of the internal random pool.

/usr[/local]/share/gnupg/options.skel

The skeleton options file.

/usr[/local]/lib/gnupg/

Default location for extensions.

Operation is further controlled by a few environment variables:

HOME

Used to locate the default home directory.

GNUPGHOME

If set directory used instead of "~/.gnupg".

GPG_AGENT_INFO

Used to locate the gpg-agent. 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.

PINENTRY_USER_DATA

This value is passed via gpg-agent to pinentry. It is useful to convey extra information to a custom pinentry.

COLUMNS

LINES

Used to size some displays to the full size of the screen.

LANGUAGE

Apart from its use by GNU, it is used in the W32 version to override the language selection done through the Registry. If used and set to a valid and available language name (langid), the file with the translation is loaded from gpgdir/gnupg.nls/langid.mo. Here gpgdir is the directory out of which the gpg binary has been loaded. If it can't be loaded the Registry is tried and as last resort the native Windows locale system is used.

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 (which may contain passphrases or other sensitive material) 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.

Note also that some systems (especially laptops) have the ability to ``suspend to disk'' (also known as ``safe sleep'' or ``hibernate''). This writes all memory to disk before going into a low power or even powered off mode. Unless measures are taken in the operating system to protect the saved memory, passphrases or other sensitive material may be recoverable from it later.

SEE ALSO

The full documentation for this tool is maintained as a Texinfo manual. If GnuPG and the info program are properly installed at your site, the command

info gnupg

should give you access to the complete manual including a menu structure and an index.