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[$sfaqheader=The GnuPG FAQ says:]
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The most recent version of the FAQ is available from
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<http://www.gnupg.org/>
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[$maintainer=David D. Scribner, <faq 'at' gnupg.org>]
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[$hGPG=http://www.gnupg.org]
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[H body bgcolor=#ffffff text=#000000 link=#1f00ff alink=#ff0000 vlink=#9900dd]
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[H H1]GnuPG Frequently Asked Questions[H /H1]
18
Last-Modified: Aug 21, 2002[H br]
19
Maintained-by: [$maintainer]
23
This is the GnuPG FAQ. The latest HTML version is available
24
[H a href=[$hGPG]/faq.html]here[H/a].
26
The index is generated automatically, so there may be errors here. Not
27
all questions may be in the section they belong to. Suggestions about
28
how to improve the structure of this FAQ are welcome.
30
Please send additions and corrections to the maintainer. It would be
31
most convenient if you could provide the answer to be included here
32
as well. Your help is very much appreciated.
34
Please, don't send message like "This should be a FAQ - what's the answer?".
35
If it hasn't been asked before, it isn't a FAQ. In that case you could
36
search in the mailing list archive.
47
[H a href=[$hGPG]]GnuPG[H /a] stands for GNU Privacy Guard and
48
is GNU's tool for secure communication and data storage. It can be
49
used to encrypt data and to create digital signatures. It includes
50
an advanced key management facility and is compliant with the
51
proposed OpenPGP Internet standard as described in [H a href=http://www.gnupg.org/rfc2440.html]RFC 2440[H/a].
52
As such, it is aimed to be compatible with PGP from NAI, Inc.
54
<Q> Is GnuPG compatible with PGP?
56
In general, yes. GnuPG and newer PGP releases should be implementing
57
the OpenPGP standard. But there are some interoperability
58
problems. See question <Rcompat> for details.
61
<S> SOURCES of INFORMATION
63
<Q> Where can I find more information?
65
Here's a list of on-line resources:
68
[H LI]The documentation page is located at [H a href=[$hGPG]/docs.html]<[$hGPG]/docs.html>[H/a].
69
Have a look at the HOWTOs and the GNU Privacy Handbook (GPH, available
70
in English, Spanish and Russian). The latter provides a detailed user's
71
guide to GnuPG. You'll also find a document about how to convert from
74
[H LI]On [H a href=http://lists.gnupg.org]<http://lists.gnupg.org>[H/a] you'll find an online archive of the
75
GnuPG mailing lists. Most interesting should be gnupg-users for all
76
user-related issues and gnupg-devel if you want to get in touch with
79
In addition, searchable archives can be found on MARC, e.g.: [H br]
80
GnuPG-users: [H a href=http://marc.theaimsgroup.com/?l=gnupg-users&r=1&w=2]<http://marc.theaimsgroup.com/?l=gnupg-users&r=1&w=2>[H/a],[H br]
81
GnuPG-devel: [H a href=http://marc.theaimsgroup.com/?l=gnupg-devel&r=1&w=2]<http://marc.theaimsgroup.com/?l=gnupg-devel&r=1&w=2>[H/a].[H br]
84
Before posting to a list, read this FAQ and the available
85
documentation. In addition, search the list archive - maybe your
86
question has already been discussed. This way you help people focus
87
on topics that have not yet been resolved.
89
[H LI]The GnuPG source distribution contains a subdirectory:
95
where some additional documentation is located (mainly interesting
96
for hackers, not the casual user).
99
<Q> Where do I get GnuPG?
101
You can download the GNU Privacy Guard from its primary FTP server
102
[H a href=ftp://ftp.gnupg.org/pub/gcrypt]ftp.gnupg.org[H /a] or from one of the mirrors:
104
[H a href=[$hGPG]/mirrors.html]
105
<[$hGPG]/mirror.html>
108
The current version is 1.0.4, please upgrade to this version as it
109
fixes a security bug regarding the verification of multiple signatures.
114
<Q> Which OSes does GnuPG run on?
116
It should run on most Unices as well as Windows 95 and Windows NT. A
117
list of OSes reported to be OK is presented at:
119
[H a href=http://www.gnupg.org/backend.html#supsys]
120
<http://www.gnupg.org/gnupg.html#supsys>
123
<Q> Which random gatherer should I use?
125
"Good" random numbers are crucial for the security of your encryption.
126
Different operating systems provide a variety of more or less quality
127
random data. Linux and *BSD provide kernel generated random data
128
through /dev/random - this should be the preferred choice on these
129
systems. Also Solaris users with the SUNWski package installed have
130
a /dev/random. In these cases, use the configure option:
133
--enable-static-rnd=linux
136
In addition, there's also the kernel random device by Andi Maier
137
[H a href= http://www.cosy.sbg.ac.at/~andi]<http://www.cosy.sbg.ac.at/~andi>[H /a], but it's still beta. Use at your
140
On other systems, the Entropy Gathering Daemon (EGD) is a good choice.
141
It is a perl-daemon that monitors system activity and hashes it into
142
random data. See the download page [H a href=http://www.gnupg.org/download.html]<http://www.gnupg.org/download.html>[H /a]
146
--enable-static-rnd=egd
151
If the above options do not work, you can use the random number
152
generator "unix". This is [H B]very[H /B] slow and should be avoiced. The
153
random quality isn't very good so don't use it on sensitive data.
156
<Q> How do I include support for RSA and IDEA?
158
RSA is included as of GnuPG 1.0.3.
160
The official GnuPG distribution does not contain IDEA due to a
161
patent restriction. The patent does not expire before 2007 so don't
162
expect official support before then.
164
However, there is an unofficial module to include it even
165
in earlier versions of GnuPG. It's available from
166
[H a href=ftp://ftp.gnupg.org/pub/gcrypt/contrib/]<ftp://ftp.gnupg.org/pub/gcrypt/contrib/>[H /a]. Look for:
172
Compilation directives are in the headers of these files. Then add
173
the following line to your ~/.gnupg/options:
182
<Q> What is the recommended key size?
184
1024 bit for DSA signatures; even for plain ElGamal signatures
185
this is sufficient as the size of the hash is probably the weakest
186
link if the key size is larger than 1024 bits. Encryption keys may
187
have greater sizes, but you should then check the fingerprint of
191
gpg --fingerprint <user ID>
194
As for the key algorithms, you should stick with the default (i.e.,
195
DSA signature and ElGamal encryption). A ElGamal signing key has the
196
following disadvantages: the signature is larger, it is hard to
197
create such a key useful for signatures which can withstand some
198
real world attacks, you don't get any extra security compared to
199
DSA, and there might be compatibility problems with certain PGP
200
versions. It has only been introduced because at the time it was
201
not clear whether there was a patent on DSA.
203
<Q> Why does it sometimes take so long to create keys?
205
The problem here is that we need a lot of random bytes and for that
206
we (on Linux the /dev/random device) must collect some random data.
207
It is really not easy to fill the Linux internal entropy buffer; I
208
talked to Ted Ts'o and he commented that the best way to fill the
209
buffer is to play with your keyboard. Good security has its price.
210
What I do is to hit several times on the shift, control, alternate,
211
and caps lock keys, because these keys do not produce output to the
212
screen. This way you get your keys really fast (it's the same thing
215
Another problem might be another program which eats up your random
216
bytes (a program (look at your daemons) that reads from /dev/random).
218
<Q> And it really takes long when I work on a remote system. Why?
220
Don't do this at all! You should never create keys or even use GnuPG
221
on a remote system because you normally have no physical control
222
over your secret key ring (which is in most cases vulnerable to
223
advanced dictionary attacks) - I strongly encourage everyone to only
224
create keys on a local computer (a disconnected laptop is probably
225
the best choice) and if you need it on your connected box (I know:
226
We all do this) be sure to have a strong password for your account
227
and for your secret key and that you can trust your system
230
When I check GnuPG on a remote system via ssh (I have no Alpha here
231
;-) I have the same problem. It takes a *very* long time to create
232
the keys, so I use a special option, --quick-random, to generate
233
insecure keys which are only good for some tests.
235
<Q> What is the difference between options and commands?
237
If you do a 'gpg --help', you will get two separate lists. The first
238
is a list of commands. The second is a list of options. Whenever you
239
run GPG, you [H B]must[H /B] pick exactly one command (with one exception,
240
see below). You [H B]may[H /B] pick one or more options. The command should,
241
just by convention, come at the end of the argument list, after all
242
the options. If the command takes a file (all the basic ones do),
243
the filename comes at the very end. So the basic way to run gpg is:
246
gpg [--option something] [--option2] [--option3 something] --command file
249
Some options take arguments. For example, the --output option (which
250
can be abbreviated -o) is an option that takes a filename. The
251
option's argument must follow immediately after the option itself,
252
otherwise gpg doesn't know which option the argument is supposed to
253
go with. As an option, --output and its filename must come before
254
the command. The --recipient (-r) option takes a name or keyid to
255
encrypt the message to, which must come right after the -r argument.
256
The --encrypt (or -e) command comes after all the options followed
257
by the file you wish to encrypt. So use:
260
gpg -r alice -o secret.txt -e test.txt
263
If you write the options out in full, it is easier to read:
266
gpg --recipient alice --output secret.txt --encrypt test.txt
269
If you're saving it in a file called ".txt" then you'd probably
270
expect to see ASCII-armored text in there, so you need to add the
271
--armor (-a) option, which doesn't take any arguments:
274
gpg --armor --recipient alice --output secret.txt --encrypt test.txt
277
If you imagine square brackets around the optional parts, it becomes
281
gpg [--armor] [--recipient alice] [--output secret.txt] --encrypt test.txt
284
The optional parts can be rearranged any way you want:
287
gpg --output secret.txt --recipient alice --armor --encrypt test.txt
290
If your filename begins with a hyphen (e.g. "-a.txt"), GnuPG assumes
291
this is an option and may complain. To avoid this you have either
292
to use "./-a.txt" or stop the option and command processing with two
293
hyphens: "-- -a.txt". [H B]The exception:[H /B] signing and encrypting at the
297
gpg [--options] --sign --encrypt foo.txt
300
<Q> I can't delete a user ID because it is already deleted on my public
303
Because you can only select from the public key ring, there is no
304
direct way to do this. However it is not very complicated to do
305
anyway. Create a new user ID with exactly the same name and you
306
will see that there are now two identical user IDs on the secret
307
ring. Now select this user ID and delete it. Both user IDs will be
308
removed from the secret ring.
310
<Q> I can't delete the secret key because my public key disappeared?
312
To select a key a search is always done on the public keyring,
313
therefore it is not possible to select an secret key without
314
having the public key. Normally it shoud never happen that the
315
public key got lost but the secret key is still available. The
316
reality is different, so GnuPG implements a special way to deal
317
with it: Simply use the long keyid which can be obtained by using
318
the --with-colons options (it is the fifth field in the lines
319
beginning with "sec").
321
<Q> What are trust, validity and ownertrust?
323
"ownertrust" is used instead of "trust" to make clear that this is
324
the value you have assigned to a key to express how much you trust
325
the owner of this key to correctly sign (and so introduce) other
326
keys. "validity", or calculated trust, is a value which says how
327
much GnuPG thinks a key is valid (that it really belongs to the one
328
who claims to be the owner of the key). For more see the chapter
329
"The Web of Trust" in the Manual.
331
<Q> How do I sign a patch file?
333
Use "gpg --clearsign --not-dash-escaped ...". The problem with
334
--clearsign is that all lines starting with a dash are quoted with
335
"- "; obviously diff produces many lines starting with a dash and
336
these are then quoted and that is not good for a patch ;-). To use a
337
patch file without removing the cleartext signature, the special
338
option --not-dash-escaped may be used to suppress generation of
339
these escape sequences. You should not mail such a patch because
340
spaces and line endings are also subject to the signature and a
341
mailer may not preserve these. If you want to mail a file you can
342
simply sign it using your MUA.
344
<Q> Where is the "encrypt-to-self" option?
346
Use "--encrypt-to your_keyid". You can use more than one of these
347
options. To temporarily override the use of this additional key,
348
you can use the option "--no-encrypt-to".
350
<Q> How can I get rid of the Version and Comment headers in armored
353
Use "--no-version --comment ''". Note that the left over blank line
354
is required by the protocol.
356
<Q> What does the "You are using the xxxx character set." mean?
358
This note is printed when UTF8 mapping has to be done. Make sure
359
that the displayed charset is the one you have activated on your
360
system. Since "iso-8859-1" is the charset most used, this is the
361
default. You can change the charset with the option "--charset".
362
It is important that your active character set matches the one
363
displayed - if not, restrict yourself to plain 7 bit ASCII and no
364
mapping has to be done.
366
<Q> How can a get list of key IDs used to encrypt a message?
369
gpg --batch --decrypt --list-only --status-fd 1 2>/dev/null | \
370
awk '/^\[GNUPG:\] ENC_TO / { print $3 }'
373
<Q> I can't decrypt my symmetrical only (-c) encrypted message with
374
a new version of GnuPG.
376
There used to be a bug in GnuPG < 1.0.1 which happens only if 3DES
377
or Twofish has been used for symmetric only encryption (this has
378
never been the default). The bug has been fixed but to enable you
379
to decrypt old messages, you should run gpg with the option
380
"--emulate-3des-s2k-bug", decrypt the message and encrypt it again
381
without this option. The option will be removed in 1.1, so better
382
re-encrypt your message now.
384
<Q> How can I use GnuPG in an automated environment?
386
You should use the option --batch and don't use pass phrases as
387
there is usually no way to store it more secure than the secret
388
keyring itself. The suggested way to create the keys for the
389
automated environment is:
393
[H LI] If you want to do automatic signing, create a signing
394
subkey for your key (edit menu, choose "addkey" and the DSA).
395
[H LI] Make sure that you use a passphrase (needed by the current
397
[H LI] gpg --export-secret-subkeys --no-comment foo >secring.auto
398
[H LI] Copy secring.auto and the public keyring to a test directory.
399
[H LI] Change to this directory.
400
[H LI] gpg --homedir . --edit foo and use "passwd" to remove the
401
passphrase from the subkeys. You may also want to remove all
403
[H LI] Copy secring.auto to a floppy and carry it to the target box.
406
On the target machine:
408
[H LI] Install secring.auto as secret keyring.
409
[H LI] Now you can start your new service. It is a good idea to
410
install some intrusion detection system so that you hopefully
411
get a notice of an successful intrusion, so that you in turn
412
can revoke all the subkeys installed on that machine and
416
<Q> Which email-client can I use with GnuPG?
418
Using GnuPG to encrypt email is one of the most popular uses.
419
Several mail clients or mail user-agents (MUA) support GnuPG at
420
varying degrees. Simplifying a bit, there are two ways mail can be
421
encrypted with GnuPG: the "old style" ASCII armor, i.e. plain text
422
encryption, and RFC2015 style (previously PGP/MIME, now OpenPGP).
423
The latter has full MIME support. Some MUAs support only one of
424
them, so whichever you actually use depends on your needs as well
425
as the capabilities of your addressee.
427
The following list is probably not exhaustive:
429
OpenPGP: Mutt (Unix), Emacs/Mew, Becky2 (Windows, with plugin),
430
TkRat (Unix). There is effort for a Mozilla plugin and
431
Emacs/GNUS has support in the current CVS.
433
ASCII: Emacs/{VM,GNUS}/MailCrypt, Mutt(Unix), Pine(Unix), and
436
Good overviews of OpenPGP-support can be found at
437
[H a href=http://cryptorights.org/pgp-users/pgp-mail-clients.html]http://cryptorights.org/pgp-users/pgp-mail-clients.html[H /a]
438
and [H a href=http://www.geocities.com/openpgp/courrier_en.html]http://www.geocities.com/openpgp/courrier_en.html[H /a].
440
<Q> Can't we have a gpg library?
442
This has been frequently requested. However, the current viewpoint
443
of the GnuPG maintainers is that this would lead to several security
444
issues and will therefore not be implemented in the foreseeable
445
future. However, for some areas of application gpgme could do the
446
trick. You'll find it at [H a href=ftp://ftp.guug.de/pub/gcrypt/alpha/gpgme]ftp://ftp.guug.de/pub/gcrypt/alpha/gpgme[H /a].
448
<Q> I have successfully generated a revocation certificate, but I don't
449
understand how to send it to the key servers.
451
Most keyservers don't accept a 'bare' revocation certificate. You
452
have to import the certificate into gpg first:
455
gpg --import my-revocation.asc
458
then send the revoked key to the keyservers:
461
gpg --keyserver certserver.pgp.com --send-keys mykeyid
464
(or use a keyserver web interface for this).
466
<Q> How do I put my keyring in a different directory?
468
GnuPG keeps several files in a special homedir directory. These
469
include the options file, pubring.gpg, secring.gpg, trustdb.gpg,
470
and others. GnuPG will always create and use these files. On unices,
471
the homedir is usually ~/.gnupg; on Windows "C:\gnupg\".
473
If you want to put your keyrings somewhere else, use:
479
to make GnuPG create all its files in that directory. Your keyring
480
will be "/my/path/pubring.gpg". This way you can store your secrets
481
on a floppy disk. Don't use "--keyring" as its purpose is to specify
482
additional keyring files.
485
<S> COMPATIBILITY ISSUES
488
<Q> How can I encrypt a message with GnuPG so that PGP is able to decrypt it?
490
It depends on the PGP version.
494
You can't do that because PGP 2.x normally uses IDEA which is not
495
supported by GnuPG as it is patented (see <Ridea>), but if you have a
496
modified version of PGP you can try this:
499
gpg --rfc1991 --cipher-algo 3des ...
502
Please don't pipe the data to encrypt to gpg but provide it using a
503
filename; otherwise, PGP 2 will not be able to handle it.
505
As for conventional encryption, you can't do this for PGP 2.
507
[H LI]PGP 5.x and higher[H br]
508
You need to provide two additional options:
511
--compress-algo 1 --cipher-algo cast5
514
You may also use "3des" instead of "cast5", and "blowfish" does not
515
work with all versions of PGP 5. You may also want to put:
521
into your ~/.gnupg/options file - this does not affect normal GnuPG
524
This applies to conventional encryption as well.
527
<Q> How do I migrate from PGP 2.x to GnuPG?
529
PGP 2 uses the RSA and IDEA encryption algorithms. Whereas the RSA
530
patent has expired and RSA is included as of GnuPG 1.0.3, the IDEA
531
algorithm is still patented until 2007. Under certain conditions you
532
may use IDEA even today. In that case, you may refer to Question
533
<Ridea> about how to add IDEA support to GnuPG and read
534
[H a href=http://www.gnupg.org/gph/en/pgp2x.html]http://www.gnupg.org/gph/en/pgp2x.html[H /a] to perform the migration.
540
<Q> Why is PGP 5.x not able to encrypt messages with some keys?
542
PGP, Inc. refuses to accept ElGamal keys of type 20 even for
543
encryption. They only support type 16 (which is identical at least
544
for decryption). To be more inter-operable, GnuPG (starting with
545
version 0.3.3) now also uses type 16 for the ElGamal subkey which is
546
created if the default key algorithm is chosen. You may add a type
547
16 ElGamal key to your public key, which is easy as your key
548
signatures are still valid.
550
<Q> Why is PGP 5.x not able to verify my messages?
552
PGP 5.x does not accept v4 signatures for data material but OpenPGP
553
requests generation of v4 signatures for all kind of data, that's why
554
GnuPG defaults to them. Use the option "--force-v3-sigs" to generate
555
v3 signatures for data.
557
<Q> How do I transfer owner trust values from PGP to GnuPG?
559
There is a script in the tools directory to help you. After you have
560
imported the PGP keyring you can give this command:
563
$ lspgpot pgpkeyring | gpg --import-ownertrust
566
where pgpkeyring is the original keyring and not the GnuPG keyring
567
you might have created in the first step.
569
<Q> PGP does not like my secret key.
571
Older PGPs probably bail out on some private comment packets used by
572
GnuPG. These packets are fully in compliance with OpenPGP; however
573
PGP is not really OpenPGP aware. A workaround is to export the
574
secret keys with this command:
577
$ gpg --export-secret-keys --no-comment -a your-key-id
580
Another possibility is this: by default, GnuPG encrypts your secret
581
key using the Blowfish symmetric algorithm. Older PGPs will only
582
understand 3DES, CAST5, or IDEA symmetric algorithms. Using the
583
following method you can re-encrypt your secret gpg key with a
587
$ gpg --s2k-cipher-algo=CAST5 --s2k-digest-algo=SHA1 \
588
--compress-algo=1 --edit-key <username>
591
Then use passwd to change the password (just change it to the same
592
thing, but it will encrypt the key with CAST5 this time).
594
Now you can export it and PGP should be able to handle it.
596
For PGP 6.x the following options work to export a key:
599
$ gpg --s2k-cipher-algo 3des --compress-algo 1 --rfc1991 \
600
--export-secret-keys <key-ID>
604
<S> PROBLEMS and ERROR MESSAGES
606
<Q> Why do I get "gpg: Warning: using insecure memory!"
608
On many systems this program should be installed as setuid(root).
609
This is necessary to lock memory pages. Locking memory pages prevents
610
the operating system from writing them to disk and thereby keeping your
611
secret keys really secret. If you get no warning message about insecure
612
memory your operating system supports locking without being root. The
613
program drops root privileges as soon as locked memory is allocated.
615
On UnixWare 2.x and 7.x you should install GnuPG with the 'plock'
616
privilege to get the same effect:
619
filepriv -f plock /path/to/gpg
622
If you can't or don't want to install GnuPG setuid(root), you can
623
use the option "--no-secmem-warning" or put:
629
in your ~/.gnupg/options file (this disables the warning).
631
On some systems (e.g., Windows) GnuPG does not lock memory pages
632
and older GnuPG versions (<=1.0.4) issue the warning:
635
gpg: Please note that you don't have secure memory
638
This warning can't be switched off by the above option because it
639
was thought to be too serious an issue. However, it confused users
640
too much, so the warning was eventually removed.
642
<Q> Large File Support doesn't work ...
644
LFS is correctly working in post-1.0.4 CVS. If configure doesn't
645
detect it correctly, try a different (i.e., better) compiler. egcs
646
1.1.2 works fine, other gccs sometimes don't. BTW, several
647
compilation problems of GnuPG 1.0.3 and 1.0.4 on HP-UX and Solaris
648
were due to broken LFS support.
650
<Q> In the edit menu the trust values is not displayed correctly after
653
This happens because some information is stored immediately in
654
the trustdb, but the actual trust calculation can be done after the
655
save command. This is a "not easy to fix" design bug which will be
656
addressed in some future release.
658
<Q> What does "skipping pubkey 1: already loaded" mean?
660
As of GnuPG 1.0.3, the RSA algorithm is included. If you still have
661
a "load-extension rsa" in your options file, the above message
662
occurs. Just remove the load command from the options file.
664
<Q> GnuPG 1.0.4 doesn't create ~/.gnupg ...
666
That's a known bug, already fixed in newer versions.
668
<Q> An ElGamal signature does not verify anymore since version 1.0.2 ...
670
Use the option --emulate-md-encode-bug.
672
<Q> Old versions of GnuPG can't verify ElGamal signatures
674
Update to GnuPG 1.0.2 or newer.
676
<Q> When I use --clearsign, the plain text has sometimes extra dashes
679
This is called dash-escaped text and is required by OpenPGP.
680
It always happens when a line starts with a dash ("-") and is
681
needed to make the lines that structure signature and text
682
(i.e., "-----BEGIN PGP SIGNATURE-----") to be the only lines
683
that start with two dashes.
685
If you use GnuPG to process those messages, the extra dashes
686
are removed. Good mail clients remove those extra dashes when
687
displaying such a message.
689
<Q> What is the thing with "can't handle multiple signatures"?
691
Due to different message formats GnuPG is not always able to split
692
a file with multiple signatures unambiguously into its parts. This
693
error message informs you that there is something wrong with the input.
695
The only way to have multiple signatures in a file is by using the
696
OpenPGP format with one-pass-signature packets (which is GnuPG's
697
default) or the cleartext signed format.
699
<Q> If I submit a key to a keyserver, nothing happens ...
701
You are most likely using GnuPG 1.0.2 or older on Windows. That's
702
feature isn't yet implemented, but it's a bug not to say it. Newer
703
versions issue a warning. Upgrade to 1.0.4 or newer.
705
<Q> I get "gpg: waiting for lock ..."
707
A previous gpg has most likely exited abnormally and left a lock
708
file. Go to ~/.gnupg and look for .*.lock files and remove them.
710
<Q> Older gpg's (e.g., 1.0) have problems with keys from newer gpgs ...
712
As of 1.0.3, keys generated with gpg are created with preferences to
713
TWOFISH (and AES since 1.0.4) and that also means that they have the
714
capability to use the new MDC encryption method. This will go into
715
OpenPGP soon and is also suppoted by PGP 7. This new method avoids
716
a (not so new) attack on all email encryption systems.
718
This in turn means that pre-1.0.3 gpg's have problems with newer
719
keys. Because of security fixes, you should keep your GnuPG
720
installation in a recent state anyway. As a workaround, you can
721
force gpg to use a previous default cipher algo by putting:
727
into your options file.
729
<Q> With 1.0.4, I get "this cipher algorithm is deprecated ..."
731
If you just generated a new key and get this message while
732
encrypting, you've witnessed a bug in 1.0.4. It uses the new AES
733
cipher Rijndael that is incorrectly being referred as "deprecated".
734
Ignore this warning, more recent versions of gpg are corrected.
736
<Q> Some dates are displayed as ????-??-??, why?
738
Due to constraints in most libc implementations, dates beyond
739
2038-01-19 can't be displayed correctly. 64 bit OSes are not
740
affected by this problem. To avoid printing wrong dates, GnuPG
741
instead prints some question marks. To see the correct value, you
742
can use the options --with-colons and --fixed-list-mode.
744
<Q> I still have a problem. How do I report a bug?
746
Are you sure that it's not been mentioned somewhere on the mailing
747
lists? Did you have a look at the bug list (you'll find a link to
748
the list of reported bugs on the documentation page). If you're not
749
sure about it being a bug, you can send mail to the gnupg-devel
750
list. Otherwise, use the GUUG bug tracking system
751
[H a href=http://bugs.guug.de/Reporting.html]http://bugs.guug.de/Reporting.html[H /a].
753
<Q> Why doesn't GnuPG support X509 certificates?
755
GnuPG, first and foremost, is an implementation of the OpenPGP
756
standard (RFC 2440), which is a competing infrastructure, different
759
They are both public-key cryptosystems, but how the public keys are
760
actually handled is different.
762
<Q> Why do national characters in my user ID look funny?
764
According to OpenPGP, GnuPG encodes user ID strings (and other
765
things) using UTF-8. In this encoding of Unicode, most national
766
characters get encoded as two- or three-byte sequences. For
767
example, å (0xE5 in ISO-8859-1) becomes Ã¥ (0xC3,
768
0xA5). This might also be the reason why keyservers can't find
771
<Q> I get 'sed' errors when running ./configure on Mac OS X ...
773
This will be fixed after GnuPG has been upgraded to autoconf-2.50.
774
Until then, find the line setting CDPATH in the configure script
783
<Q> Why does GnuPG 1.0.6 bail out on keyrings used with 1.0.7?
785
There is a small bug in 1.0.6 which didn't parse trust packets
786
correctly. You may want to apply this patch if you can't upgrade:
789
http://www.gnupg.org/developer/gpg-woody-fix.txt
795
<Q> How does this whole thing work?
797
To generate a secret/public keypair, run:
803
and choose the default values.
805
Data that is encrypted with a public key can only be decrypted by
806
the matching secret key. The secret key is protected by a password,
807
the public key is not.
809
So to send your friend a message, you would encrypt your message
810
with his public key, and he would only be able to decrypt it by
811
having the secret key and putting in the password to use his secret
814
GnuPG is also useful for signing things. Things that are encrypted
815
with the secret key can be decrypted with the public key. To sign
816
something, a hash is taken of the data, and then the hash is in some
817
form encoded with the secret key. If someone has your public key, they
818
can verify that it is from you and that it hasn't changed by checking
819
the encoded form of the hash with the public key.
821
A keyring is just a large file that stores keys. You have a public
822
keyring where you store yours and your friend's public keys. You have
823
a secret keyring that you keep your secret key on, and should be very
824
careful with. Never ever give anyone else access to it and use a *good*
825
passphrase to protect the data in it.
827
You can 'conventionally' encrypt something by using the option 'gpg -c'.
828
It is encrypted using a passphrase, and does not use public and secret
829
keys. If the person you send the data to knows that passphrase, they
830
can decrypt it. This is usually most useful for encrypting things to
831
yourself, although you can encrypt things to your own public key in the
832
same way. It should be used for communication with partners you know
833
and where it is easy to exchange the passphrases (e.g. with your boy
834
friend or your wife). The advantage is that you can change the
835
passphrase from time to time and decrease the risk, that many old
836
messages may be decrypted by people who accidently got your passphrase.
838
You can add and copy keys to and from your keyring with the 'gpg
839
--import' and 'gpg --export' option. 'gpg --export-secret-keys' will
840
export secret keys. This is normally not useful, but you can generate
841
the key on one machine then move it to another machine.
843
Keys can be signed under the 'gpg --edit-key' option. When you sign a
844
key, you are saying that you are certain that the key belongs to the
845
person it says it comes from. You should be very sure that is really
846
that person: You should verify the key fingerprint with:
849
gpg --fingerprint user-id
852
over the phone (if you really know the voice of the other person), at a
853
key signing party (which are often held at computer conferences), or at
854
a meeting of your local GNU/Linux User Group.
856
Hmm, what else. You may use the option "-o filename" to force output
857
to this filename (use "-" to force output to stdout). "-r" just lets
858
you specify the recipient (which public key you encrypt with) on the
859
command line instead of typing it interactively.
861
Oh yeah, this is important. By default all data is encrypted in some
862
weird binary format. If you want to have things appear in ASCII text
863
that is readable, just add the '-a' option. But the preferred method
864
is to use a MIME aware mail reader (Mutt, Pine and many more).
866
There is a small security glitch in the OpenPGP (and therefore GnuPG)
867
system; to avoid this you should always sign and encrypt a message
868
instead of only encrypting it.
870
<Q> Why are some signatures with an ELG-E key valid?
872
These are ElGamal keys generated by GnuPG in v3 (RFC 1991) packets.
873
The OpenPGP draft later changed the algorithm identifier for ElGamal
874
keys which are usable for signatures and encryption from 16 to 20.
875
GnuPG now uses 20 when it generates new ElGamal keys but still
876
accepts 16 (which is according to OpenPGP "encryption only") if this
877
key is in a v3 packet. GnuPG is the only program which had used
878
these v3 ElGamal keys - so this assumption is quite safe.
880
<Q> How does the whole trust thing work?
882
It works more or less like PGP. The difference is that the trust is
883
computed at the time it is needed. This is one of the reasons for
884
the trustdb which holds a list of valid key signatures. If you are
885
not running in batch mode you will be asked to assign a trust
886
parameter (ownertrust) to a key.
888
You can see the validity (calculated trust value) using this
892
gpg --list-keys --with-colons
895
If the first field is "pub" or "uid", the second field shows you the
899
o = Unknown (this key is new to the system)
900
e = The key has expired
901
q = Undefined (no value assigned)
902
n = Don't trust this key at all
903
m = There is marginal trust in this key
904
f = The key is full trusted
905
u = The key is ultimately trusted; this is only used
906
for keys for which the secret key is also available.
907
r = The key has been revoked
908
d = The key has been disabled
911
The value in the "pub" record is the best one of all "uid" records.
912
You can get a list of the assigned trust values (how much you trust
913
the owner to correctly sign another person's key) with:
916
gpg --list-ownertrust
919
The first field is the fingerprint of the primary key, the second
920
field is the assigned value:
923
- = No Ownertrust value yet assigned.
924
n = Never trust this keyholder to correctly verify others signatures.
925
m = Have marginal trust in the keyholders capability to sign other
927
f = Assume that the key holder really knows how to sign keys.
928
u = No need to trust ourself because we have the secret key.
931
Keep these values confidential because they express your opinions
932
about others. PGP stores this information with the keyring thus it
933
is not a good idea to publish a PGP keyring instead of exporting the
934
keyring. GnuPG stores the trust in the trustdb.gpg file so it is okay
935
to give a gpg keyring away (but we have a --export command too).
937
<Q> What kind of output is this: "key C26EE891.298, uid 09FB: ...."?
939
This is the internal representation of a user ID in the trustdb.
940
"C26EE891" is the keyid, "298" is the local ID (a record number in
941
the trustdb) and "09FB" is the last two bytes of a ripe-md-160 hash
942
of the user ID for this key.
944
<Q> How do I interpret some of the informational outputs?
946
While checking the validity of a key, GnuPG sometimes prints some
947
information which is prefixed with information about the checked
954
This is about the key with key ID 12345678 and the internal number
955
3456, which is the record number of the so called directory record
959
"uid 12345678.3456/ACDE"
962
This is about the user ID for the same key. To identify the user ID
963
the last two bytes of a ripe-md-160 over the user ID ring is printed.
966
"sig 12345678.3456/ACDE/9A8B7C6D"
969
This is about the signature with key ID 9A8B7C6D for the above key
970
and user ID, if it is a signature which is direct on a key, the user
971
ID part is empty (..//..).
973
<Q> Are the header lines of a cleartext signature part of the signed
976
No. For example you can add or remove "Comment:" lines. They have
977
a purpose like the mail header lines. However a "Hash:" line is
978
needed for OpenPGP signatures to tell the parser which hash
981
<Q> What is the list of preferred algorithms?
983
The list of preferred algorithms is a list of cipher, hash and
984
compression algorithms stored in the self-signature of a key during
985
key generation. When you encrypt a document, GnuPG uses this list
986
(which is then part of a public key) to determine which algorithms
987
to use. Basically it tells other people what algorithms the
988
recipient is able to handle and provides an order of preference.
990
<Q> How do I change the list of preferred algorithms?
992
In version 1.0.7 or later, you can use the edit menu and set the
993
new list of preference using the command "setpref"; the format of
994
this command resembles the output of the command "pref". The
995
preference is not changed immediately but the set preference will
996
be used when a new user ID is created. If you want to update the
997
preferences for existing user IDs, select those user IDs (or select
998
none to update all) and enter the command "updpref". Note that the
999
timestamp of the self-signature is increased by one second when
1000
running this command.
1003
<S> ACKNOWLEDGEMENTS
1005
Many thanks to Nils Ellmenreich for maintaining this FAQ file for
1006
a long time, Werner Koch for the original FAQ file, and to all
1007
posters to gnupg-users and gnupg-devel. They all provided most
1010
Also thanks to Casper Dik for providing us with a script to generate
1011
this FAQ (he uses it for the excellent Solaris2 FAQ).
1015
Copyright (C) 2000-2002 Free Software Foundation, Inc.,
1016
59 Temple Place - Suite 330, Boston, MA 02111, USA
1018
Verbatim copying and distribution of this entire article is permitted in
1019
any medium, provided this notice is preserved.
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removed
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