gpg

Name

gpg – encryption and signing tool

Synopsis

gpg
 [--homedir name]
 [--options file]
 [options]
 command
 [args]

DESCRIPTION

gpg is the main program for the GnuPG system.

This man page does only list the commands and options available. For a more verbose documentation get the GNU Privacy Handbook (GPH), which is available at http://www.gnupg.org/gph/ . You will find a list of HOWTO documents at http://www.gnupg.org/docs.html .

COMMANDS

gpg recognizes these commands:

-s, –sign
Make a signature. This command may be combined with –encrypt.
–clearsign
Make a clear text signature.
-b, –detach-sign
Make a detached signature.
-e, –encrypt
Encrypt data. This option may be combined with –sign.
-c, –symmetric
Encrypt with symmetric cipher only This command asks for a passphrase.
–store
Store only (make a simple RFC1991 packet).
–decrypt [=file=]
Decrypt file (or stdin if no file is specified) and write it to stdout (or the file specified with –output). If the decrypted file is signed, the signature is also verified. This command differs from the default operation, as it never writes to the filename which is included in the file and it rejects files which don't begin with an encrypted message.
–verify [[=sigfile=] [=signed-files=]]
Assume that sigfile is a signature and verify it without generating any output. With no arguments, the signature packet is read from stdin (it may be a detached signature when not used in batch mode). 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 (if such a file does not exist it is expected at stdin; use a single dash ("-") as filename to force a read from stdin). With more than 1 argument, the first should be a detached signature and the remaining files are the signed stuff.
–verify-files [=files=]
This is a special version of the –verify command which does not work with detached signatures. The command expects the files to bee verified either on the commandline or reads the filenames from stdin; each anem muts be on separate line. The command is intended for quick checking of many files.
–list-keys [=names=], –list-public-keys [=names=]
List all keys from the public keyrings, or just the ones given on the command line.
–list-secret-keys [=names=]
List all keys from the secret keyrings, or just the ones given on the command line.
–list-sigs [=names=]
Same as –list-keys, but the signatures are listed too.
–check-sigs [=names=]
Same as –list-sigs, but the signatures are verified.
–fingerprint [=names=]
List all keys with their fingerprints. This is the same output as –list-keys but with the additional output of a line with the fingerprint. May also be combined with –list-sigs or –check-sigs. If this command is given twice, the fingerprints of all secondary keys are listed too.
–list-packets
List only the sequence of packets. This is mainly useful for debugging.
–gen-key
Generate a new key pair. This command is normally only used interactive.

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

–edit-key name
Present a menu which enables you to do all key related tasks:
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.
revsig
Revoke a signature. GnuPG asks for every signature which has been done by one of the secret keys, whether a revocation certificate should be generated.
trust
Change the owner trust value. This updates the trust-db immediately and no save is required.
disable, enable
Disable or enable an entire key. A disabled key can normally not be used for encryption.
adduid
Create an alternate user id.
deluid
Delete an user id.
addkey
Add a subkey to this key.
delkey
Remove a subkey.
revkey
Revoke a subkey.
expire
Change the key expiration time. If a key is selected, the time of this key will be changed. With no selection the key expiration of the primary key is changed.
passwd
Change the passphrase of the secret key.
uid n
Toggle selection of user id with index n. Use 0 to deselect all.
key n
Toggle selection of subkey with index n. Use 0 to deselect all.
check
Check all selected user ids.
pref
List preferences.
toggle
Toggle between public and secret key listing.
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.
q
Not enough information for calculation.
n
Never trust this key.
m
Marginally trusted.
f
Fully trusted.
u
Ultimately trusted.
–sign-key name
Sign a public key with you secret key. This is a shortcut version of the subcommand "sign" from –edit.
–lsign-key name
Sign a public key with you secret key but mark it as non-exportable. This is a shortcut version of the subcommand "lsign" from –edit.
–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 be able to check the validity of a given recipient's or signator's key.
–delete-key name
Remove key from the public keyring
–delete-secret-key name
Remove key from the secret and public keyring
–gen-revoke
Generate a revocation certificate for the complete key. To revoke a subkey or a signature, use the –edit command.
–export [=names=]
Either export all keys from all keyrings (default keyrings and those registered via option –keyring), or if at least one name is given, those of the given name. The new keyring is written to stdout or to the file given with option "output". Use together with –armor to mail those keys.
–send-keys [=names=]
Same as –export but sends the keys to a keyserver. Option –keyserver must be used to give the name of this keyserver. Don't send your complete keyring to a keyserver - select only those keys which are new or changed by you.
–export-all [=names=]
Same as –export, but does also export keys which are not compatible to OpenPGP.
(no term)
–export-secret-keys [=names=], –export-secret-subkeys [=names=] :: Same as –export, but does export the secret keys. 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 successful import such a key.
–import [=files=], –fast-import [=files=]
Import/merge keys. This adds the given keys to the keyring. The fast version does not build the trustdb; this can be done at any time with the command –update-trustdb.

There are a few other options which control how this command works. Most notable here is the –merge-only options 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 HKP keyserver. Option –keyserver must be used to give the name of this keyserver.
–export-ownertrust
List the assigned ownertrust values in ASCII format for backup purposes
–import-ownertrust [=files=]
Update the trustdb with the ownertrust values stored in files (or stdin if not given); existing values will be overwritten.
–print-md algo [=files=]
Print message digest of algorithm ALGO for all given files of stdin. If "*" is used for the algorithm, digests for all available algorithms are printed.
–gen-random 0|1|2 [=count=]
Emit COUNT random bytes of the given quality level. If count is not given or zero, an endless sequence of random bytes will be emitted. PLEASE, don't use this command unless you know what you are doing, it may remove precious entropy from the system!
–gen-prime mode bits [=qbits=]
Use the source, Luke :-). The output format is still subject to change.
–version
Print version information along with a list of supported algorithms.
–warranty
Print warranty information.
-h, –help
Print usage information. This is a really long list even it does list not all options.

OPTIONS

Long options can be put in an options file (default "~/.gnupg/options"). Do not write the 2 dashes, but simply the name of the option and any required arguments. Lines with a hash as the first non-white-space character are ignored. Commands may be put in this file too, but that does not make sense.

gpg recognizes these options:

-a, –armor
Create ASCII armored output.
-o, –output file
Write output to file.
-u, –local-user name
Use name as the user ID to sign. This option is silently ignored for the list commands, so that it can be used in an options file.
–default-key name
Use name as default user ID for signatures. If this is not used the default user ID is the first user ID found in the secret keyring.
-r, –recipient name,
Encrypt for user id name. If this option is not specified, GnuPG asks for the user-id unless –default-recipient is given
–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 a 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.
–encrypt-to name
Same as –recipient but this one is intended for in the options file and may be used together with an 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.
–no-encrypt-to
Disable the use of all –encrypt-to keys.
-v, –verbose
Give more information during processing. If used twice, the input data is listed in detail.
-q, –quiet
Try to be as quiet as possible.
-z n
Set compression level to n. A value of 0 for n disables compression. Default is to use the default compression level of zlib (normally 6).
-t, –textmode
Use canonical text mode. If -t (but not –textmode) is used together with armoring and signing, this enables clearsigned messages. This kludge is needed for PGP compatibility; normally you would use –sign or –clearsign to selected the type of the signature.
-n, –dry-run
Don't make any changes (this is not completely implemented).
-i, –interactive
Prompt before overwriting any files.
–batch
Use batch mode. Never ask, do not allow interactive commands.
–no-tty
Make sure that the TTY (terminal) is never used for any output. This option is needed in some cases because GnuPG sometimes prints warnings to the TTY if if –batch is used.
–no-batch
Disable batch mode. This may be of use if –batch is enabled from an options file.
–yes
Assume "yes" on most questions.
–no
Assume "no" on most questions.
–always-trust
Skip key validation and assume that used keys are always fully trusted. You won't use this unless you have installed some external validation scheme.
–keyserver name
Use name to lookup keys which are not yet in your keyring. This is only done while verifying messages with signatures. The option is also required for the command –send-keys to specify the keyserver to where the keys should be send. All keyservers synchronize with each other - so there is no need to send keys to more than one server. Using the command "host -l pgp.net | grep wwwkeys" gives you a list of keyservers. Because there is load balancing using round-robin DNS you may notice that you get different key servers.
–no-auto-key-retrieve
This option disables the automatic retrieving of keys from a keyserver while verifying signatures. This option allows to keep a keyserver in the options file or the –send-keys and –recv-keys commands.
–honor-http-proxy
Try to access the keyserver over the proxy set with the variable "http\proxy".
–keyring file
Add file to the 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 home-directory ("~/.gnupg" if –homedir is not used). The filename may be prefixed with a scheme:

"gnupg-ring:" is the default one.

"gnupg-gdbm:" may be used for a GDBM ring. Note that GDBM is experimental and likely to be removed in future versions.

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

–secret-keyring file
Same as –keyring but for the secret keyrings.
–homedir directory
Set the name of the home directory to directory If this option is not used it defaults to "~/.gnupg". It does not make sense to use this in a options file. This also overrides the environment variable "GNUPGHOME".
–charset name
Set the name of the native character set. This is used to convert some strings to proper UTF-8 encoding. Valid values for name are:
iso-8859-1
This is the default Latin 1 set.
iso-8859-2
The Latin 2 set.
koi8-r
The usual Russian set (rfc1489).
–utf8-strings, –no-utf8-strings
Assume that the arguments are already given as UTF8 strings. The default (–no-utf8-strings) is to assume that arguments are encoded in the character set as specified by –charset. These options effects all following arguments. Both options may 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.
–load-extension name
Load an extension module. If name does not contain a slash it is searched in "/usr/local/lib/gnupg" See the manual for more information about extensions.
–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.
–status-fd n
Write special status strings to the file descriptor n. See the file DETAILS in the documentation for a listing of them.
–logger-fd n
Write log output to file descriptor n and not to stderr.
–no-comment
Do not write comment packets. This option affects only the generation of secret keys. Please note, that this has nothing to do with the comments in clear text signatures.
–comment string
Use string as comment string in clear text signatures. To suppress those comment strings entirely, use an empty string here.
–default-comment
Force to write the standard comment string in clear text signatures. Use this to overwrite a –comment from a config file.
–no-version
Omit the version string in clear text signatures.
–emit-version
Force to write the version string in clear text signatures. Use this to overwrite a previous –no-version from a config file.
-N, –notation-data name=value
Put the name value pair into the signature as notation data. name must consists only of alphanumeric characters, digits or the underscore; the first character must not be a digit. value may be any printable string; it will encoded in UTF8, so sou should have check that your –charset is set right. If you prefix name with an exclamation mark, the notation data will be flagged as critical (rfc2440:5.2.3.15).
–set-policy-url string
Use string as Policy URL for signatures (rfc2440:5.2.3.19). If you prefix it with an exclamation mark, the policy URL packet will be flagged as critical.
–set-filename string
Use string as the name of file which is stored in messages.
–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.
–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).
–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.
–digest-algo name
Use name as message digest algorithm. Running the program with the command –version yields a list of supported algorithms. Please note that using this option may violate the OpenPGP requirement, that a 160 bit hash is to be used for DSA.
–s2k-cipher-algo name
Use name as the cipher algorithm used to protect secret keys. The default cipher is BLOWFISH. This cipher is also used for conventional encryption if –cipher-algo is not given.
–s2k-digest-algo name
Use name as the digest algorithm used to mangle the passphrases. The default algorithm is RIPE-MD-160. This digest algorithm is also used for conventional encryption if –digest-algo is not given.
–s2k-mode n
Selects how passphrases are mangled. If n is 0 a plain passphrase (which is not recommended) will be used, a 1 (default) adds a salt to the passphrase and a 3 iterates the whole process a couple of times. Unless –rfc1991 is used, this mode is also used for conventional encryption.
–compress-algo n
Use compress algorithm n. Default is 2 which is RFC1950 compression. You may use 1 to use the old zlib version (RFC1951) which is used by PGP. The default algorithm may give better results because the window size is not limited to 8K. If this is not used the OpenPGP behavior is used, i.e. the compression algorithm is selected from the preferences; note, that this can't be done if you do not encrypt the data.
–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-keyid
Do not put the keyid into encrypted packets. This option hides the receiver of the message and is a countermeasure against traffic analysis. It may slow down the decryption process because all available secret keys are tried.
–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
Because some mailers change lines starting with "From " to "<From " it is good to handle such lines in a special way when creating cleartext signatures. All other PGP versions do it this way too. This option is not enabled by default because it would violate rfc2440.
–passphrase-fd n
Read the passphrase 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. Don't use this option if you can avoid it.
–command-fd n
This is a replacement for the depreciated 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.
–rfc1991
Try to be more RFC1991 (PGP 2.x) compliant.
–openpgp
Reset all packet, cipher and digest options to OpenPGP behavior. Use this option to reset all previous options like –rfc1991, –force-v3-sigs, –s2k-*, –cipher-algo, –digest-algo and –compress-algo to OpenPGP compliant values. All PGP workarounds are also disabled.
–force-v3-sigs
OpenPGP states that an implementation should generate v4 signatures but PGP 5.x recognizes v4 signatures only on key material. This options forces v3 signatures for signatures on data.
–force-mdc
Force the use of encryption with appended manipulation code. This is always used with the newer cipher (those with a blocksize greater than 64 bit). This option might not be implemented yet.
–allow-non-selfsigned-uid
Allow the import of keys with user IDs which are not self-signed. This is only allows the import - key validation will fail and you have to check the validity of the key my other means. This hack is needed for some German keys generated with pgp 2.6.3in. You should really avoid using it, because OpenPGP has better mechanics to do separate signing and encryption keys.
–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.
–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 standalone encryption system will probably use this. Improper usage of this option may lead to data and key corruption.
–no-random-seed-file
GnuPG uses a file to store it's internal random pool over invocations. This makes random generation faster; however sometimes write operations are not desired. This option can be used to achive that with the cost of slower random generation.
–no-verbose
Reset verbose level to 0.
–no-greeting
Suppress the initial copyright message but do not enter batch mode.
–no-secmem-warning
Suppress the warning about "using insecure memory".
–no-armor
Assume the input data is not in ASCII armored format.
–no-default-keyring
Do not add the default keyrings to the list of 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-colons
Print key listings delimited by colons.
–with-key-data
Print key listings delimited by colons and print the public key data.
–with-fingerprint
Same as the command –fingerprint but changes only the format of the output and may be used together with another command.
–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 excact behaviour of this option may change in future versions.
–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 does only skip the actual decryption pass and therefore enables a fast listing of the encryption keys.
–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.
–emulate-md-encode-bug
GnuPG versions prior to 1.0.2 had a bug in the way a signature was encode. This options enables a workaround by checking faulty signatures again with the encoding used in old versions. This may only happen for ElGamal signatures which are not widely used.
–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.
–merge-only
Don't insert new keys into the keyrings while doing an import.
–try-all-secrets
Don't look at the key ID as stored in the message but try all secret keys in turn to find the right decryption key. This option forces the behaviour as used by anonymous recipients (created by using –throw-keyid) and might come handy in case where an encrypted message contains a bogus key ID.

How to specify a user ID

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

  • :: Used to locate the default home directory.
  • Here the key ID is given in the usual short form.
  • 234AABBCC34567C4, 0F323456784E56EAB, 01AB3FED1347A5612, 0x234AABBCC34567C4 :: Here the key ID is given in the long form as used by OpenPGP.
  • 1234343434343434C434343434343434, 123434343434343C3434343434343734349A3434, 0E12343434343434343434EAB3484343434343434, 0xE12343434343434343434EAB3484343434343434 :: The best way to specify a key ID is by using the fingerprint of the key. This avoids any ambiguities in case that there are duplicated key IDs (which are really rare for the long key IDs).
  • Using an exact to match string. The equal sign indicates this.
  • Using the email address part which must match exactly. The left angle bracket indicates this email address mode.
  • All words must match exactly (not case sensitive) but can appear in any order in the user ID. Words are any sequences of letters, digits, the underscore and all characters with bit 7 set.
  • Using the Local ID. This is a very low level method and should only be used by applications which really need it. The hash character indicates this method. An application should not assume that this is only a number.
  • By case insensitive substring matching. This is the default mode but applications may want to explicitely indicate this by putting the asterisk in front.

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.

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 –list-keys user_ID
show keys
gpg –fingerprint user_ID
show fingerprint
gpg –verify pgpfile, gpg –verify sigfile [=files=]
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 of binary) and [=files=] are the signed data; if this is not given the name of the file holding the signed data is constructed by cutting off the extension (".asc" or ".sig") of sigfile or by asking the user for the filename.

ENVIRONMENT

HOME
Used to locate the default home directory.
GNUPGHOME
If set directory used instead of "~/.gnupg".
http\proxy
Only honored when the option –honor-http-proxy is set.

FILES

~/.gnupg/secring.gpg
The secret keyring
~/.gnupg/secring.gpg.lock
and the lock file
~/.gnupg/pubring.gpg
The public keyring
~/.gnupg/pubring.gpg.lock
and the lock file
~/.gnupg/trustdb.gpg
The trust database
~/.gnupg/trustdb.gpg.lock
and the lock file
~/.gnupg/random\seed
used to preserve the internal random pool
~/.gnupg/options
May contain options
/usr[/local]/share/gnupg/options.skel
Skeleton options file
usr[/local]/lib/gnupg
Default location for extensions

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!

BUGS

On many systems this program should be installed as setuid(root). This is necessary to lock memory pages. Locking memory pages prevents the operating system from writing memory pages to disk. If you get no warning message about insecure memory 3our operating system supports locking without being root. The program drops root privileges as soon as locked memory is allocated.

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