PGP Encryption vs. GPG? Whats's the difference

jbaird123
jbaird123 used Ask the Experts™
on
Can someone explain to me the difference between PGP and GPG encryption?  I'm currently working for a company that uses PGP encryption to encrypt files, and I am using a 3rd party tool (Talend) to move / encrypt files, but this tool to my knowledge only supports GPG.  Are these two things similar or compatible?  Is it possible to encrypt to PGP using a GPG tool?
Comment
Watch Question

Do more with

Expert Office
EXPERT OFFICE® is a registered trademark of EXPERTS EXCHANGE®
PGP is both a company, and a private encryption standard.

GPG is the OpenPGP standard.

In effect, the same thing....

Hope that helps. Here's some links for your info.

http://www.pgp.com/products/platform/index.html
http://www.gnupg.org/

Author

Commented:
I need a little more clarification:

If a file is encrypted using PGP, can it be decrypted using GPG?  What about the other way around?

In other words, when decrypting a file, is it necessary to know whether it was encrypted with PGP or GPG?
Okay, in general, YES they are compatible. They're based on the same technology.

There's just some interoperability issues. Taken from the GPG website:

"      
GnuPG Frequently Asked Questions

Version: 1.6.3
Last-Modified: Jul 30, 2003
Maintained-by: David D. Scribner, <faq 'at' gnupg.org>

This is the GnuPG FAQ. The latest HTML version is available here.

The index is generated automatically, so there may be errors. Not all questions may be in the section they belong to. Suggestions about how to improve the structure of this FAQ are welcome.

Please send additions and corrections to the maintainer. It would be most convenient if you could provide the answer to be included here as well. Your help is very much appreciated!

Please, don't send message like "This should be a FAQ - what's the answer?". If it hasn't been asked before, it isn't a FAQ. In that case you could search in the mailing list archive.

1. GENERAL
# 1.1) What is GnuPG?
# 1.2) Is GnuPG compatible with PGP?
# 1.3) Is GnuPG free to use for personal or commercial use?
# 1.4) What conventions are used in this FAQ?
2. SOURCES of INFORMATION
# 2.1) Where can I find more information on GnuPG?
# 2.2) Where do I get GnuPG?
3. INSTALLATION
# 3.1) Which OSes does GnuPG run on?
# 3.2) Which random data gatherer should I use?
# 3.3) How do I include support for RSA and IDEA?
4. USAGE
# 4.1) What is the recommended key size?
# 4.2) Why does it sometimes take so long to create keys?
# 4.3) And it really takes long when I work on a remote system. Why?
# 4.4) What is the difference between options and commands?
# 4.5) I can't delete a user ID on my secret keyring because it has already been deleted on my public keyring. What can I do?
# 4.6) I can't delete my secret key because the public key disappeared. What can I do?
# 4.7) What are trust, validity and ownertrust?
# 4.8) How do I sign a patch file?
# 4.9) Where is the "encrypt-to-self" option?
# 4.10) How can I get rid of the Version and Comment headers in armored messages?
# 4.11) What does the "You are using the xxxx character set." mean?
# 4.12) How can I get list of key IDs used to encrypt a message?
# 4.13) Why can't I decrypt files encrypted as symmetrical-only (-c) with a version of GnuPG prior to 1.0.1.
# 4.14) How can I use GnuPG in an automated environment?
# 4.15) Which email-client can I use with GnuPG?
# 4.16) Can't we have a gpg library?
# 4.17) I have successfully generated a revocation certificate, but I don't understand how to send it to the key servers.
# 4.18) How do I put my keyring in a different directory?
# 4.19) How do I verify signed packages?
# 4.20) How do I export a keyring with only selected signatures (keys)?
# 4.21) I still have my secret key, but lost my public key. What can I do?
# 4.22) Clearsigned messages sent from my web-mail account have an invalid signature. Why?
5. COMPATIBILITY ISSUES
# 5.1) How can I encrypt a message with GnuPG so that PGP is able to decrypt it?
# 5.2) How do I migrate from PGP 2.x to GnuPG?
# 5.3) (removed)
# 5.4) Why is PGP 5.x not able to encrypt messages with some keys?
# 5.5) Why is PGP 5.x not able to verify my messages?
# 5.6) How do I transfer owner trust values from PGP to GnuPG?
# 5.7) PGP does not like my secret key.
# 5.8) GnuPG no longer installs a ~/.gnupg/options file. Is it missing?
# 5.9) How do you export GnuPG keys for use with PGP?
6. PROBLEMS and ERROR MESSAGES
# 6.1) Why do I get "gpg: Warning: using insecure memory!"
# 6.2) Large File Support doesn't work ...
# 6.3) In the edit menu the trust values are not displayed correctly after signing uids. Why?
# 6.4) What does "skipping pubkey 1: already loaded" mean?
# 6.5) GnuPG 1.0.4 doesn't create ~/.gnupg ...
# 6.6) An Elgamal signature does not verify anymore since version 1.0.2 ...
# 6.7) Old versions of GnuPG can't verify Elgamal signatures
# 6.8) When I use --clearsign, the plain text has sometimes extra dashes in it - why?
# 6.9) What is the thing with "can't handle multiple signatures"?
# 6.10) If I submit a key to a keyserver, nothing happens ...
# 6.11) I get "gpg: waiting for lock ..."
# 6.12) Older gpg binaries (e.g., 1.0) have problems with keys from newer gpg binaries ...
# 6.13) With 1.0.4, I get "this cipher algorithm is deprecated ..."
# 6.14) Some dates are displayed as ????-??-??. Why?
# 6.15) I still have a problem. How do I report a bug?
# 6.16) Why doesn't GnuPG support X.509 certificates?
# 6.17) Why do national characters in my user ID look funny?
# 6.18) I get 'sed' errors when running ./configure on Mac OS X ...
# 6.19) Why does GnuPG 1.0.6 bail out on keyrings used with 1.0.7?
# 6.20) I upgraded to GnuPG version 1.0.7 and now it takes longer to load my keyrings. What can I do?
# 6.21) Doesn't a fully trusted user ID on a key prevent warning messages when encrypting to other IDs on the key?
# 6.22) I just compiled GnuPG from source on my GNU/Linux RPM-based system and it's not working. Why?
7. ADVANCED TOPICS
# 7.1) How does this whole thing work?
# 7.2) Why are some signatures with an ELG-E key valid?
# 7.3) How does the whole trust thing work?
# 7.4) What kind of output is this: "key C26EE891.298, uid 09FB: ...."?
# 7.5) How do I interpret some of the informational outputs?
# 7.6) Are the header lines of a cleartext signature part of the signed material?
# 7.7) What is the list of preferred algorithms?
# 7.8) How do I change the list of preferred algorithms?
8. ACKNOWLEDGEMENTS

1. GENERAL

1.1) What is GnuPG?

GnuPG stands for GNU Privacy Guard and is GNU's tool for secure communication and data storage. It can be used to encrypt data and to create digital signatures. It includes an advanced key management facility and is compliant with the proposed OpenPGP Internet standard as described in RFC 2440. As such, it is aimed to be compatible with PGP from PGP Corp. and other OpenPGP tools

1.2) Is GnuPG compatible with PGP?

In general, yes. GnuPG and newer PGP releases should be implementing the OpenPGP standard. But there are some interoperability problems. See question 5.1 for details.

1.3) Is GnuPG free to use for personal or commercial use?

Yes. GnuPG is part of the GNU family of tools and applications built and provided in accordance with the Free Software Foundation (FSF) General Public License (GPL). Therefore the software is free to copy, use, modify and distribute in accordance with that license. Please read the file titled COPYING that accompanies the application for more information.

1.4) What conventions are used in this FAQ?

Although GnuPG is being developed for several operating systems (often in parallel), the conventions used in this FAQ reflect a UNIX shell environment. For Win32 users, references to a shell prompt (`$') should be interpreted as a command prompt (`>'), directory names separated by a forward slash (`/') may need to be converted to a back slash (`\'), and a tilde (`~') represents a user's "home" directory (reference question 4.18 for an example).

Some command-lines presented in this FAQ are too long to properly display in some browsers for the web page version of this file, and have been split into two or more lines. For these commands please remember to enter the entire command-string on one line or the command will error, or at minimum not give the desired results.

Please keep in mind that this FAQ contains information that may not apply to your particular version, as new features and bug fixes are added on a continuing basis (reference the NEWS file included with the source or package for noteworthy changes between versions). One item to note is that starting with GnuPG version 1.1.92 the file containing user options and settings has been renamed from "options" to "gpg.conf". Information in the FAQ that relates to the options file may be interchangable with the newer gpg.conf file in many instances. See question 5.8 for details.

2. SOURCES of INFORMATION

2.1) Where can I find more information on GnuPG?

On-line resources:

    * The documentation page is located at <http://www.gnupg.org/documentation/>. Also, have a look at the HOWTOs and the GNU Privacy Handbook (GPH, available in English, Spanish and Russian). The latter provides a detailed user's guide to GnuPG. You'll also find a document about how to convert from PGP 2.x to GnuPG.

    * At <http://www.gnupg.org/documentation/mailing-lists.html> you'll find an online archive of the GnuPG mailing lists. Most interesting should be gnupg-users for all user-related issues and gnupg-devel if you want to get in touch with the developers.

      In addition, searchable archives can be found on MARC, e.g.:
      gnupg-users: <http://marc.theaimsgroup.com/?l=gnupg-users&r=1&w=2>
      gnupg-devel: <http://marc.theaimsgroup.com/?l=gnupg-devel&r=1&w=2>

      PLEASE: Before posting to a list, read this FAQ and the available documentation. In addition, search the list archive - maybe your question has already been discussed. This way you help people focus on topics that have not yet been resolved.

    * The GnuPG source distribution contains a subdirectory:

      ./doc

      where some additional documentation is located (mainly interesting for hackers, not the casual user).

2.2) Where do I get GnuPG?

You can download the GNU Privacy Guard from its primary FTP server <ftp://ftp.gnupg.org/gcrypt/> or from one of the mirrors:

<http://www.gnupg.org/download/mirrors.html>

The current stable version is 1.2.2. Please upgrade to this version as it includes additional features, functions and security fixes that may not have existed in prior versions.

3. INSTALLATION

3.1) Which OSes does GnuPG run on?

It should run on most Unices as well as Windows versions (including Windows NT/2000) and Macintosh OS/X. A list of OSes reported to be OK is presented at:

<http://www.gnupg.org/download/supported_systems.html>

3.2) Which random data gatherer should I use?

"Good" random numbers are crucial for the security of your encryption. Different operating systems provide a variety of more or less quality random data. Linux and *BSD provide kernel generated random data through /dev/random - this should be the preferred choice on these systems. Also Solaris users with the SUNWski package installed have a /dev/random. In these cases, use the configure option:

--enable-static-rnd=linux

In addition, there's also the kernel random device by Andi Maier <http://www.cosy.sbg.ac.at/~andi/SUNrand/>, but it's still beta. Use at your own risk!

On other systems, the Entropy Gathering Daemon (EGD) is a good choice. It is a perl-daemon that monitors system activity and hashes it into random data. See the download page <http://www.gnupg.org/download/> to obtain EGD. Use:

--enable-static-rnd=egd

here.

If the above options do not work, you can use the random number generator "unix". This is very slow and should be avoided. The random quality isn't very good so don't use it on sensitive data.

3.3) How do I include support for RSA and IDEA?

RSA is included as of GnuPG version 1.0.3.

The official GnuPG distribution does not contain IDEA due to a patent restriction. The patent does not expire before 2007 so don't expect official support before then.

However, there is an unofficial module to include it even in earlier versions of GnuPG. It's available from <ftp://ftp.gnupg.dk/pub/contrib-dk/>. Look for:

 idea.c.gz        (c module)
 idea.c.gz.sig    (signature file)

 ideadll.zip      (c module and win32 dll)
 ideadll.zip.sig  (signature file)

Compilation directives are in the headers of these files. You will then need to add the following line to your ~/.gnupg/gpg.conf or ~/.gnupg/options file:

load-extension idea

4. USAGE

4.1) What is the recommended key size?

1024 bit for DSA signatures; even for plain Elgamal signatures. This is sufficient as the size of the hash is probably the weakest link if the key size is larger than 1024 bits. Encryption keys may have greater sizes, but you should then check the fingerprint of this key:

$ gpg --fingerprint <user ID>

As for the key algorithms, you should stick with the default (i.e., DSA signature and Elgamal encryption). An Elgamal signing key has the following disadvantages: the signature is larger, it is hard to create such a key useful for signatures which can withstand some real world attacks, you don't get any extra security compared to DSA, and there might be compatibility problems with certain PGP versions. It has only been introduced because at the time it was not clear whether there was a patent on DSA.

4.2) Why does it sometimes take so long to create keys?

The problem here is that we need a lot of random bytes and for that we (on Linux the /dev/random device) must collect some random data. It is really not easy to fill the Linux internal entropy buffer; I talked to Ted Ts'o and he commented that the best way to fill the buffer is to play with your keyboard. Good security has its price. What I do is to hit several times on the shift, control, alternate, and caps lock keys, because these keys do not produce output to the screen. This way you get your keys really fast (it's the same thing PGP2 does).

Another problem might be another program which eats up your random bytes (a program (look at your daemons) that reads from /dev/random).

4.3) And it really takes long when I work on a remote system. Why?

Don't do this at all! You should never create keys or even use GnuPG on a remote system because you normally have no physical control over your secret key ring (which is in most cases vulnerable to advanced dictionary attacks) - I strongly encourage everyone to only create keys on a local computer (a disconnected laptop is probably the best choice) and if you need it on your connected box (I know, we all do this) be sure to have a strong password for both your account and for your secret key, and that you can trust your system administrator.

When I check GnuPG on a remote system via ssh (I have no Alpha here) ;-) I have the same problem. It takes a *very* long time to create the keys, so I use a special option, --quick-random, to generate insecure keys which are only good for some tests.

4.4) What is the difference between options and commands?

If you do a 'gpg --help', you will get two separate lists. The first is a list of commands. The second is a list of options. Whenever you run GPG, you must pick exactly one command (with one exception, see below). You may pick one or more options. The command should, just by convention, come at the end of the argument list, after all the options. If the command takes a file (all the basic ones do), the filename comes at the very end. So the basic way to run gpg is:

$ gpg [--option something] [--option2] [--option3 something] --command file

Some options take arguments. For example, the --output option (which can be abbreviated as -o) is an option that takes a filename. The option's argument must follow immediately after the option itself, otherwise gpg doesn't know which option the argument is supposed to paired with. As an option, --output and its filename must come before the command. The --recipient (-r) option takes a name or keyID to encrypt the message to, which must come right after the -r option. The --encrypt (or -e) command comes after all the options and is followed by the file you wish to encrypt. Therefore in this example the command-line issued would be:

$ gpg -r alice -o secret.txt -e test.txt

If you write the options out in full, it is easier to read:

$ gpg --recipient alice --output secret.txt --encrypt test.txt

If you're encrypting to a file with the extension ".txt", then you'd probably expect to see ASCII-armored text in the file (not binary), so you need to add the --armor (-a) option, which doesn't take any arguments:

$ gpg --armor --recipient alice --output secret.txt --encrypt test.txt

If you imagine square brackets around the optional parts, it becomes a bit clearer:

$ gpg [--armor] [--recipient alice] [--output secret.txt] --encrypt test.txt

The optional parts can be rearranged any way you want:

$ gpg --output secret.txt --recipient alice --armor --encrypt test.txt

If your filename begins with a hyphen (e.g. "-a.txt"), GnuPG assumes this is an option and may complain. To avoid this you have to either use "./-a.txt", or stop the option and command processing with two hyphens: "-- -a.txt".

The exception to using only one command: signing and encrypting at the same time. For this you can combine both commands, such as in:

$ gpg [--options] --sign --encrypt foo.txt

4.5) I can't delete a user ID on my secret keyring because it has already been deleted on my public keyring. What can I do?

Because you can only select from the public key ring, there is no direct way to do this. However it is not very complicated to do anyway. Create a new user ID with exactly the same name and you will see that there are now two identical user IDs on the secret ring. Now select this user ID and delete it. Both user IDs will be removed from the secret ring.

4.6) I can't delete my secret key because the public key disappeared. What can I do?

To select a key a search is always done on the public keyring, therefore it is not possible to select a secret key without having the public key. Normally it should never happen that the public key got lost but the secret key is still available. The reality is different, so GnuPG implements a special way to deal with it: Simply use the long keyID to specify the key to delete, which can be obtained by using the --with-colons options (it is the fifth field in the lines beginning with "sec").

If you've lost your public key and need to recreate it instead for continued use with your secret key, you may be able to use gpgsplit as detailed in question 4.21.

4.7) What are trust, validity and ownertrust?

With GnuPG, the term "ownertrust" is used instead of "trust" to help clarify that this is the value you have assigned to a key to express how much you trust the owner of this key to correctly sign (and thereby introduce) other keys. The "validity", or calculated trust, is a value which indicates how much GnuPG considers a key as being valid (that it really belongs to the one who claims to be the owner of the key). For more information on trust values see the chapter "The Web of Trust" in The GNU Privacy Handbook.

4.8) How do I sign a patch file?

Use "gpg --clearsign --not-dash-escaped ...". The problem with --clearsign is that all lines starting with a dash are quoted with "- "; obviously diff produces many lines starting with a dash and these are then quoted and that is not good for a patch ;-). To use a patch file without removing the cleartext signature, the special option --not-dash-escaped may be used to suppress generation of these escape sequences. You should not mail such a patch because spaces and line endings are also subject to the signature and a mailer may not preserve these. If you want to mail a file you can simply sign it using your MUA (Mail User Agent).

4.9) Where is the "encrypt-to-self" option?

Use "--encrypt-to your_keyID". You can use more than one of these options. To temporarily override the use of this additional key, you can use the option "--no-encrypt-to".

4.10) How can I get rid of the Version and Comment headers in armored messages?

Use "--no-version --comment ''". Note that the left over blank line is required by the protocol.

4.11) What does the "You are using the xxxx character set." mean?

This note is printed when UTF-8 mapping has to be done. Make sure that the displayed character set is the one you have activated on your system. Since "iso-8859-1" is the character set most used, this is the default. You can change the charset with the option "--charset". It is important that your active character set matches the one displayed - if not, restrict yourself to plain 7 bit ASCII and no mapping has to be done.

4.12) How can I get list of key IDs used to encrypt a message?

$ gpg --batch --decrypt --list-only --status-fd 1 2>/dev/null | awk '/^\[GNUPG:\] ENC_TO / { print $3 }'

4.13) Why can't I decrypt files encrypted as symmetrical-only (-c) with a version of GnuPG prior to 1.0.1.

There was a bug in GnuPG versions prior to 1.0.1 which affected files only if 3DES or Twofish was used for symmetric-only encryption (this has never been the default). The bug has been fixed, but to enable decryption of old files you should run gpg with the option "--emulate-3des-s2k-bug", decrypt the file and encrypt it again without this option.

NOTE: This option was removed in GnuPG development version 1.1.0 and later updates, so you will need to use a version between 1.0.1 and 1.0.7 to re-encrypt any affected files.

4.14) How can I use GnuPG in an automated environment?

You should use the option --batch and don't use passphrases as there is usually no way to store it more securely than on the secret keyring itself. The suggested way to create keys for an automated environment is:

On a secure machine:

   1. If you want to do automatic signing, create a signing subkey for your key (use the interactive key editing menu by issueing the command 'gpg --edit-key keyID', enter "addkey" and select the DSA key type).
   2. Make sure that you use a passphrase (needed by the current implementation).
   3. gpg --export-secret-subkeys --no-comment foo >secring.auto
   4. Copy secring.auto and the public keyring to a test directory.
   5. Change to this directory.
   6. gpg --homedir . --edit foo and use "passwd" to remove the passphrase from the subkeys. You may also want to remove all unused subkeys.
   7. Copy secring.auto to a floppy and carry it to the target box.

On the target machine:

   1. Install secring.auto as the secret keyring.
   2. Now you can start your new service. It's also a good idea to install an intrusion detection system so that you hopefully get a notice of an successful intrusion, so that you in turn can revoke all the subkeys installed on that machine and install new subkeys.

4.15) Which email-client can I use with GnuPG?

Using GnuPG to encrypt email is one of the most popular uses. Several mail clients or mail user agents (MUAs) support GnuPG to varying degrees. Simplifying a bit, there are two ways mail can be encrypted with GnuPG: the "old style" ASCII armor (i.e. cleartext encryption), and RFC 2015 style (previously PGP/MIME, now OpenPGP). The latter has full MIME support. Some MUAs support only one of them, so whichever you actually use depends on your needs as well as the capabilities of your addressee. As well, support may be native to the MUA, or provided via "plug-ins" or external tools.

The following list is not exhaustive:

 MUA            OpenPGP ASCII   How? (N,P,T)
 -------------------------------------------------------------
 Calypso           N      Y      P (Unixmail)
 Elm               N      Y      T (mailpgp,morepgp)
 Elm ME+           N      Y      N
 Emacs/Gnus        Y      Y      T (Mailcrypt,gpg.el)
 Emacs/Mew         Y      Y      N
 Emacs/VM          N      Y      T (Mailcrypt)
 Evolution         Y      Y      N
 Exmh              Y      Y      N
 GNUMail.app       Y      Y      P (PGPBundle)
 GPGMail           Y      Y      N
 KMail (<=1.4.x)   N      Y      N
 KMail (1.5.x)     Y(P)   Y(N)   P/N
 Mozilla           Y      Y      P (Enigmail)
 Mulberry          Y      Y      P
 Mutt              Y      Y      N
 Sylpheed          Y      Y      N
 Claws-mail        Y      Y      N
 TkRat             Y      Y      N
 XEmacs/Gnus       Y      Y      T (Mailcrypt)
 XEmacs/Mew        Y      Y      N
 XEmacs/VM         N      Y      T (Mailcrypt)
 XFmail            Y      Y      N
 N - Native, P - Plug-in, T - External Tool

The following table lists proprietary MUAs. The GNU Project suggests against the use of these programs, but they are listed for interoperability reasons for your convenience.

 MUA            OpenPGP ASCII   How? (N,P,T)
 -------------------------------------------------------------
 Apple Mail        Y      Y      P (GPGMail)
 Becky2            Y      Y      P (BkGnuPG)
 Eudora            Y      Y      P (EuroraGPG)
 Eudora Pro        Y      Y      P (EudoraGPG)
 Lotus Notes       N      Y      P
 Netscape 4.x      N      Y      P
 Netscape 7.x      Y      Y      P (Enigmail)
 Novell Groupwise  N      Y      P
 Outlook           N      Y      P (G-Data)
 Outlook Express   N      Y      P (GPGOE)
 Pegasus           N      Y      P (QDPGP,PM-PGP)
 Pine              N      Y      T (pgpenvelope,(gpg|pgp)4pine)
 Postme            N      Y      P (GPGPPL)
 The Bat!          N      Y      P (Ritlabs)

Good overviews of OpenPGP-support can be found at:
<http://www.openpgp.fr.st/courrier_en.html> and
<http://www.bretschneidernet.de/tips/secmua.html>.

Users of Win32 MUAs that lack OpenPGP support may look into using GPGrelay <http://gpgrelay.sourceforge.net>, a small email-relaying server that uses GnuPG to enable many email clients to send and receive emails that conform to PGP-MIME (RFC 2015).

4.16) Can't we have a gpg library?

This has been frequently requested. However, the current viewpoint of the GnuPG maintainers is that this would lead to several security issues and will therefore not be implemented in the foreseeable future. However, for some areas of application gpgme could do the trick. You'll find it at <ftp://ftp.gnupg.org/gcrypt/alpha/gpgme>.

4.17) I have successfully generated a revocation certificate, but I don't understand how to send it to the key servers.

Most keyservers don't accept a 'bare' revocation certificate. You have to import the certificate into gpg first:

$ gpg --import my-revocation.asc

then send the revoked key to the keyservers:

$ gpg --keyserver certserver.pgp.com --send-keys mykeyid

(or use a keyserver web interface for this).

4.18) How do I put my keyring in a different directory?

GnuPG keeps several files in a special homedir directory. These include the options file, pubring.gpg, secring.gpg, trustdb.gpg, and others. GnuPG will always create and use these files. On unices, the homedir is usually ~/.gnupg; on Windows it is name "gnupg" and found below the user's application directory. Run the gpg and pass the option --version to see the name of that directory.

If you want to put your keyrings somewhere else, use the option:

--homedir /my/path/

to make GnuPG create all its files in that directory. Your keyring will be "/my/path/pubring.gpg". This way you can store your secrets on a floppy disk. Don't use "--keyring" as its purpose is to specify additional keyring files.

4.19) How do I verify signed packages?

Before you can verify the signature that accompanies a package, you must first have the vendor, organisation, or issueing person's key imported into your public keyring. To prevent GnuPG warning messages the key should also be validated (or locally signed).

You will also need to download the detached signature file along with the package. These files will usually have the same name as the package, with either a binary (.sig) or ASCII armor (.asc) extension.

Once their key has been imported, and the package and accompanying signature files have been downloaded, use:

$ gpg --verify sigfile signed-file

If the signature file has the same base name as the package file, the package can also be verified by specifying just the signature file, as GnuPG will derive the package's file name from the name given (less the .sig or .asc extension). For example, to verify a package named foobar.tar.gz against its detached binary signature file, use:

$ gpg --verify foobar.tar.gz.sig

4.20) How do I export a keyring with only selected signatures (keys)?

If you're wanting to create a keyring with only a subset of keys selected from a master keyring (for a club, user group, or company department for example), simply specify the keys you want to export:

$ gpg --armor --export key1 key2 key3 key4 > keys1-4.asc

4.21) I still have my secret key, but lost my public key. What can I do?

All OpenPGP secret keys have a copy of the public key inside them, and in a worst-case scenario, you can create yourself a new public key using the secret key.

A tool to convert a secret key into a public one has been included (it's actually a new option for gpgsplit) and is available with GnuPG versions 1.2.1 or later (or can be found in CVS). It works like this:

$ gpgsplit --no-split --secret-to-public secret.gpg >publickey.gpg

One should first try to export the secret key and convert just this one. Using the entire secret keyring should work too. After this has been done, the publickey.gpg file can be imported into GnuPG as usual.

4.22) Clearsigned messages sent from my web-mail account have an invalid signature. Why?

Check to make sure the settings for your web-based email account do not use HTML formatting for the pasted clearsigned message. This can alter the message with embedded HTML markup tags or spaces, resulting in an invalid signature. The recipient may be able to copy the signed message block to a text file for verification, or the web email service may allow you to attach the clearsigned message as a file if plaintext messages are not an option.

5. COMPATIBILITY ISSUES

5.1) How can I encrypt a message with GnuPG so that PGP is able to decrypt it?

It depends on the PGP version.

    * PGP 2.x
      You can't do that because PGP 2.x normally uses IDEA which is not supported by GnuPG as it is patented (see 3.3), but if you have a modified version of PGP you can try this:

      $ gpg --rfc1991 --cipher-algo 3des ...

      Please don't pipe the data to encrypt to gpg but provide it using a filename; otherwise, PGP 2 will not be able to handle it.

      As for conventional encryption, you can't do this for PGP 2.

    * PGP 5.x and higher
      You need to provide two additional options:

      --compress-algo 1 --cipher-algo cast5

      You may also use "3des" instead of "cast5", and "blowfish" does not work with all versions of PGP 5. You may also want to put:

      compress-algo 1

      into your ~/.gnupg/options file - this does not affect normal GnuPG operation.

      This applies to conventional encryption as well. "

Hope that helps.
Commented:
I use GNUGPG, while my co-worker uses PGP.  We are able to decrypt each other's files.

Do more with

Expert Office
Submit tech questions to Ask the Experts™ at any time to receive solutions, advice, and new ideas from leading industry professionals.

Start 7-Day Free Trial