GNU Privacy Guard
|Stable release||2.0.20 / May 10, 2013|
GNU Privacy Guard (GnuPG or GPG) is a GPL Licensed alternative to the PGP suite of cryptographic software. GnuPG is compliant with RFC 4880, which is the current IETF standards track specification of OpenPGP. Current versions of PGP (and Veridis' Filecrypt) are interoperable with GnuPG and other OpenPGP-compliant systems.
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GnuPG was initially developed by Werner Koch. Version 1.0.0 was released on September 7, 1999. The German Federal Ministry of Economics and Technology funded the documentation and the port to Microsoft Windows in 2000.
Because GnuPG is an OpenPGP standard compliant system, the history of OpenPGP is of importance. It was designed to interoperate with PGP, the email encryption program initially designed and developed by Phil Zimmermann.
Version 2.0 was released 13 November 2006. The older stable 1.x branch, whose latest version as of January 2012 is 1.4.12, will be continued in parallel with the new GnuPG 2 series because there were significant changes in the architecture of the program which will not fit every purpose.
Although the basic GnuPG program has a command line interface, there exist various front-ends that provide it with a graphical user interface. For example, GnuPG encryption support has been integrated into KMail and Evolution, the graphical e-mail clients found in KDE and GNOME, the most popular Linux desktops. There are also graphical GnuPG front-ends (Seahorse for GNOME, KGPG for KDE). For Mac OS X, the Mac GPG project provides a number of Aqua front-ends for OS integration of encryption and key management as well as GnuPG installations via Installer packages. Furthermore, the GPGTools Installer installs all related OpenPGP applications (GPG Keychain Access), plugins (GPGMail) and dependencies (MacGPG) to use GnuPG based encryption. Instant messaging applications such as Psi and Fire can automatically secure messages when GnuPG is installed and configured. Web-based software such as Horde also makes use of it. The cross-platform extension Enigmail provides GnuPG support for Mozilla Thunderbird and SeaMonkey. Similarly, Enigform provides GnuPG support for Mozilla Firefox. FireGPG was discontinued June 7, 2010.
In 2005, G10 Code and Intevation released Gpg4win, a software suite that includes GnuPG for Windows, WinPT, Gnu Privacy Assistant, and GnuPG plug-ins for Windows Explorer and Outlook. These tools are wrapped in a standard Windows installer, making it easier for GnuPG to be installed and used on Windows systems.
GnuPG encrypts messages using asymmetric keypairs individually generated by GnuPG users. The resulting public keys can be exchanged with other users in a variety of ways, such as Internet key servers. They must always be exchanged carefully to prevent identity spoofing by corrupting public key ↔ "owner" identity correspondences. It is also possible to add a cryptographic digital signature to a message, so the message integrity and sender can be verified, if a particular correspondence relied upon has not been corrupted.
GnuPG does not use patented or otherwise restricted software or algorithms, like the IDEA encryption algorithm used in PGP. (It is in fact possible to use IDEA in GnuPG by downloading a plugin for it, however this may require getting a license for some uses in some countries in which IDEA is patented.) Instead, GnuPG uses a variety of other, non-patented algorithms.
Since 1.4.13/2.0.20, GnuPG supports IDEA because the last patent of IDEA expired in 2012 (Support of IDEA is "to get rid of all the questions from folks either trying to decrypt old data or migrating keys from PGP to GnuPG", not for normal use).
- Block ciphers (symmetric encryption algorithms): IDEA, CAST5, Camellia, Triple DES, AES, Blowfish, and Twofish.
- Asymmetric-key ciphers: ElGamal and RSA
- Cryptographic hashes: RIPEMD-160, MD5, SHA-1, SHA-2, and Tiger
- Digital signatures: DSA and RSA
GnuPG is a hybrid encryption software program in that it uses a combination of conventional symmetric-key cryptography for speed, and public-key cryptography for ease of secure key exchange, typically by using the recipient's public key to encrypt a session key which is only used once. This mode of operation is part of the OpenPGP standard and has been part of PGP from its first version.
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The OpenPGP standard specifies several methods of digitally signing messages. In 2003, due to an error in a change to GnuPG intended to make one of those methods more efficient, a security vulnerability was introduced. It affected only one method of digitally signing messages, only for some releases of GnuPG (1.0.2 through 1.2.3), and there were fewer than 1000 such keys listed on the key servers. Most people did not use this method, and were in any case discouraged from doing so, so the damage caused (if any, and none has been publicly reported) would appear to have been minimal. Support for this method has been removed from GnuPG versions released after this discovery (1.2.4 and later). Two further vulnerabilities were discovered in early 2006; the first being that scripted uses of GnuPG for signature verification may result in false positives, the second that non-MIME messages were vulnerable to the injection of data which while not covered by the digital signature, would be reported as being part of the signed message. In both cases updated versions of GnuPG were made available at the time of the announcement.
GnuPG is a command-line based system, that is not written as an API which can be incorporated into other software. GPGME is an API wrapper around GnuPG which parses the output of GnuPG, and various graphical front-ends based on GPGME have been created. This currently requires an out-of-process call to the GnuPG executable for many GPGME API calls. Because GPGME makes use of a special GnuPG interface designed for machine use, a stable and maintainable API between the components is given. Possible security problems in an application do not propagate to the actual crypto code due to the process barrier.
See also 
- Claws mail – email client with GPG plugin
- Comparison of e-mail clients
- E-mail privacy
- Enigform – Firefox extension
- Enigmail – Mozilla Thunderbird plug-in
- FireGPG – Firefox extension (discontinued)
- Gpg4win – a Windows package with tools and manuals for email and file encryption
- Gpg4usb - a simplified package for Windows and Linux for portable devices (like a USB drive)
- GPGMail – OS X Mail.app plug-in
- GPGServices – OS X Services Menu plug-in
- GPGTools – an OS X package with tools for email and file encryption (incl. GPGMail, GPG Keychain Access, MacGPG2, GPG Services, ...)
- Key signing party
- KGPG – KDE graphical frontend for GnuPG,
- MCabber – Jabber client
- Mutt – email client with PGP/GPG support built-in
- Off-the-Record Messaging – also known as OTR.
- OpenPGP card – a smartcard with many GnuPG functions
- Psi (instant messaging client)
- Web of trust
- WinPT – a graphical frontend to GPG for Windows
- "GnuPg 2.0.20 released".
- GnuPG 1.4.12 released
- GnuPG-2.0 released, Werner Koch, 2006-11-13
- "Mac GNU Privacy Guard". sourceforge. Retrieved 2008-04-29.
- "GPGTools Installer". gpgtools. Retrieved 2011-03-22.
- "GnuPG Features". Retrieved October 1, 2009.
- Koch, Werner (2012-12-21). "GnuPG 1.4.13 released". gnupg-users. http://lists.gnupg.org/pipermail/gnupg-users/2012-December/045844.html. Retrieved 2013-05-19.
- Phong Q. Nguyen "Can We Trust Cryptographic Software? Cryptographic Flaws in GNU Privacy Guard v1.2.3." EUROCRYPT 2004: 555–570
- GnuPG's ElGamal signing keys compromised Werner Koch, November 27, 2003
- False positive signature verification in GnuPG Werner Koch, February 15, 2006
- GnuPG does not detect injection of unsigned data, Werner Koch, March 9, 2006
- Project home page
- A Short History of the GNU Privacy Guard, written by Werner Koch, published on GnuPG's 10th birthday
- gpg4usb - a simplified package for Windows and Linux for portable devices (like a USB drives)
- GPG4WIN - EMail-Security using GnuPG for Windows
- GNU Privacy Guard at Freecode
- Enigmail is a security extension to Mozilla Thunderbird and Seamonkey. It integrates the renowned OpenPGP standard provided by GnuPG
- Another Thunderbird/GnuPG/Enigmail howto