GNU Privacy Guard (GnuPG or GPG) is a free-software replacement for

Symantec Symantec may refer to: *An American consumer software company now known as Gen Digital Inc. *A brand of enterprise security software purchased by Broadcom Inc. Broadcom Inc. is an American designer, developer, manufacturer and global supplier ...

PGP PGP or Pgp may refer to: Science and technology * P-glycoprotein, a type of protein * Pelvic girdle pain, a pregnancy discomfort * Personal Genome Project, to sequence genomes and medical records * Pretty Good Privacy, a computer program for the ...

cryptographic Cryptography, or cryptology (from grc, , translit=kryptós "hidden, secret"; and ''graphein'', "to write", or '' -logia'', "study", respectively), is the practice and study of techniques for secure communication in the presence of adve ...

software suite. The software is compliant with RFC 4880, the IETF standards-track specification of OpenPGP. Modern versions of

are

interoperable Interoperability is a characteristic of a product or system to work with other products or systems. While the term was initially defined for information technology or systems engineering services to allow for information exchange, a broader defi ...

with GnuPG and other OpenPGP-compliant systems. GnuPG is part of the GNU Project and received major funding from the

German government The Federal Cabinet or Federal Government (german: link=no, Bundeskabinett or ') is the chief executive body of the Federal Republic of Germany. It consists of the Federal Chancellor and cabinet minister A minister is a politician who head ...

in 1999.

Overview

GnuPG is a hybrid-encryption software program because 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 used only once. This mode of operation is part of the OpenPGP standard and has been part of PGP from its first version. The GnuPG 1.x series uses an integrated cryptographic library, while the GnuPG 2.x series replaces this with

Libgcrypt Libgcrypt is a cryptography library developed as a separated module of GnuPG. It can also be used independently of GnuPG, but depends on its error-reporting library Libgpg-error. It provides functions for all fundamental cryptographic building blo ...

. GnuPG encrypts messages using asymmetric key pairs individually generated by GnuPG users. The resulting public keys may 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 A digital signature is a mathematical scheme for verifying the authenticity of digital messages or documents. A valid digital signature, where the prerequisites are satisfied, gives a recipient very high confidence that the message was created b ...

to a message, so the message integrity and sender can be verified, if a particular correspondence relied upon has not been corrupted. GnuPG also supports

symmetric encryption Symmetric-key algorithms are algorithms for cryptography that use the same cryptographic keys for both the encryption of plaintext and the decryption of ciphertext. The keys may be identical, or there may be a simple transformation to go between th ...

algorithms. By default, GnuPG uses the

AES AES may refer to: Businesses and organizations Companies * AES Corporation, an American electricity company * AES Data, former owner of Daisy Systems Holland * AES Eletropaulo, a former Brazilian electricity company * AES Andes, formerly AES Gener ...

symmetrical algorithm since version 2.1,

CAST5 In cryptography, CAST-128 (alternatively CAST5) is a symmetric-key block cipher used in a number of products, notably as the default cipher in some versions of GPG and PGP. It has also been approved for Government of Canada use by the Communic ...

was used in earlier versions. GnuPG does not use patented or otherwise restricted software or algorithms. Instead, GnuPG uses a variety of other, non-patented algorithms. For a long time, it did not support the IDEA encryption algorithm used in PGP. It was in fact possible to use IDEA in GnuPG by downloading a plugin for it, however, this might require a license for some uses in countries in which IDEA was patented. Starting with versions 1.4.13 and 2.0.20, GnuPG supports IDEA because the last patent of IDEA expired in 2012. Support of IDEA is intended "to get rid of all the questions from folks either trying to decrypt old data or migrating keys from PGP to GnuPG", and hence is not recommended for regular use. More recent releases of GnuPG 2.x ("modern" and the now deprecated "stable" series) expose most cryptographic functions and algorithms

(its cryptography library) provides, including support for elliptic curve cryptography (ECDH, ECDSA and EdDSA) in the "modern" series (i.e. since GnuPG 2.1).

Algorithms

As of 2.3 or 2.2 versions, GnuPG supports the following algorithms: ; Public key: RSA,

ElGamal In cryptography, the ElGamal encryption system is an asymmetric key encryption algorithm for public-key cryptography which is based on the Diffie–Hellman key exchange. It was described by Taher Elgamal in 1985. ElGamal encryption is used in th ...

, DSA, ECDH ( cv25519, cv448, nistp256, nistp384, nistp521, brainpoolP256r1, brainpoolP384r1, brainpoolP512r1, secp256k1), ECDSA (nistp256, nistp384, nistp521, brainpoolP256r1, brainpoolP384r1, brainpoolP512r1, secp256k1),

EdDSA In public-key cryptography, Edwards-curve Digital Signature Algorithm (EdDSA) is a digital signature scheme using a variant of Schnorr signature based on twisted Edwards curves. It is designed to be faster than existing digital signature scheme ...

(ed25519, ed448) ;

Cipher In cryptography, a cipher (or cypher) is an algorithm for performing encryption or decryption—a series of well-defined steps that can be followed as a procedure. An alternative, less common term is ''encipherment''. To encipher or encode i ...

3DES In cryptography, Triple DES (3DES or TDES), officially the Triple Data Encryption Algorithm (TDEA or Triple DEA), is a Symmetric-key algorithm, symmetric-key block cipher, which applies the Data Encryption Standard, DES cipher algorithm three ti ...

, IDEA (for backward compatibility),

, Blowfish, Twofish, AES-128, AES-192, AES-256, Camellia-128, -192 and -256 ;

Hash Hash, hashes, hash mark, or hashing may refer to: Substances * Hash (food), a coarse mixture of ingredients * Hash, a nickname for hashish, a cannabis product Hash mark *Hash mark (sports), a marking on hockey rinks and gridiron football field ...

: MD5, SHA-1,

RIPEMD-160 RIPEMD (RIPE Message Digest) is a family of cryptographic hash functions developed in 1992 (the original RIPEMD) and 1996 (other variants). There are five functions in the family: RIPEMD, RIPEMD-128, RIPEMD-160, RIPEMD-256, and RIPEMD-320, of w ...

, SHA-256, SHA-384, SHA-512, SHA-224 ; Compression: Uncompressed,

ZIP Zip, Zips or ZIP may refer to: Common uses * ZIP Code, USPS postal code * Zipper or zip, clothing fastener Science and technology Computing * ZIP (file format), a compressed archive file format ** zip, a command-line program from Info-ZIP * Zi ...

, ZLIB, BZIP2

History

GnuPG was initially developed by

Werner Koch Werner may refer to: People * Werner (name), origin of the name and people with this name as surname and given name Fictional characters * Werner (comics), a German comic book character * Werner Von Croy, a fictional character in the ''Tomb Rai ...

. The first production version, version 1.0.0, was released on September 7, 1999, almost two years after the first GnuPG release (version 0.0.0). The

German Federal Ministry of Economics and Technology The Federal Ministry for Economic Affairs and Climate Action (german: Bundesministerium für Wirtschaft und Klimaschutz, ), abbreviated BMWK (was BMWi), is a cabinet-level ministry of the Federal Republic of Germany. It was previously known as ...

funded the documentation and the port to

Microsoft Windows Windows is a group of several proprietary graphical operating system families developed and marketed by Microsoft. Each family caters to a certain sector of the computing industry. For example, Windows NT for consumers, Windows Server for serv ...

in 2000. GnuPG is a system compliant to the OpenPGP standard, thus the history of OpenPGP is of importance; it was designed to interoperate with

, an email encryption program initially designed and developed by Phil Zimmermann. On February 7, 2014, a GnuPG

crowdfunding Crowdfunding is the practice of funding a project or venture by raising money from a large number of people, typically via the internet. Crowdfunding is a form of crowdsourcing and alternative finance. In 2015, over was raised worldwide by crow ...

effort closed, raising

€ The euro sign () is the currency sign used for the euro, the official currency of the eurozone and unilaterally adopted by Kosovo and Montenegro. The design was presented to the public by the European Commission on 12 December 1996. It consists o ...

36,732 for a new Web site and infrastructure improvements.

Branches

Since the release of a stable GnuPG 2.3, starting with version 2.3.3 in October 2021, three stable branches of GnuPG are actively maintained: * A "

stable A stable is a building in which livestock, especially horses, are kept. It most commonly means a building that is divided into separate stalls for individual animals and livestock. There are many different types of stables in use today; the ...

branch", which currently is (as of 2021) the 2.3 branch. * A " LTS (long-term support) branch", which currently is (as of 2021) the 2.2 branch (which was formerly called "modern branch", in comparison to the 2.0 branch). * The old "

legacy In law, a legacy is something held and transferred to someone as their inheritance, as by will and testament. Personal effects, family property, marriage property or collective property gained by will of real property. Legacy or legacies may refer ...

branch" (formerly called "classic branch"), which is and will stay the 1.4 branch. Before GnuPG 2.3, two stable branches of GnuPG were actively maintained: * "Modern" (2.2), with numerous new features, such as elliptic curve cryptography, compared to the former "stable" (2.0) branch, which it replaced with the release of GnuPG 2.2.0 on August 28, 2017. It was initially released on November 6, 2014. * "Classic" (1.4), the very old, but still maintained stand-alone version, most suitable for outdated or embedded platforms. Initially released on December 16, 2004. Different GnuPG 2.x versions (e.g. from the 2.2 and 2.0 branches) cannot be installed at the same time. However, it is possible to install a "classic" GnuPG version (i.e. from the 1.4 branch) along with any GnuPG 2.x version. Before the release of GnuPG 2.2 ("modern"), the now deprecated "stable" branch (2.0) was recommended for general use, initially released on November 13, 2006. This branch reached its end-of-life on December 31, 2017; Its last version is 2.0.31, released on December 29, 2017. Before the release of GnuPG 2.0, all stable releases originated from a single branch; i.e., before November 13, 2006, no multiple release branches were maintained in parallel. These former, sequentially succeeding (up to 1.4) release branches were: * 1.2 branch, initially released on September 22, 2002, with 1.2.6 as the last version, released on October 26, 2004. * 1.0 branch, initially released on September 7, 1999, with 1.0.7 as the last version, released on April 30, 2002. (Note that before the release of GnuPG 2.3.0, branches with an odd minor release number (e.g. 2.1, 1.9, 1.3) were development branches leading to a stable release branch with a "+ 0.1" higher version number (e.g. 2.2, 2.0, 1.4); hence branches 2.2 and 2.1 both belong to the "modern" series, 2.0 and 1.9 both to the "stable" series, while the branches 1.4 and 1.3 both belong to the "classic" series. With the release of GnuPG 2.3.0, this nomenclature was altered to be composed of a "stable" and "LTS" branch from the "modern" series, plus 1.4 as the last maintained "classic" branch. Also note that even or odd minor release numbers do not indicate a stable or development release branch, anymore.)

Platforms

Although the basic GnuPG program has a

command-line interface A command-line interpreter or command-line processor uses a command-line interface (CLI) to receive commands from a user in the form of lines of text. This provides a means of setting parameters for the environment, invoking executables and pro ...

, there exists various front-ends that provide it with a graphical user interface. For example, GnuPG encryption support has been integrated into

KMail Kontact is a personal information manager and groupware software suite developed by KDE. It supports calendars, contacts, notes, to-do lists, news, and email. It offers a number of inter-changeable graphical UIs (KMail, KAddressBook, Akregator, ...

and Evolution, the graphical email clients found in

KDE KDE is an international Free software movement, free software community that develops free and open-source software. As a central development hub, it provides tools and resources that allow collaborative work on this kind of software. Well-know ...

and

GNOME A gnome is a mythological creature and diminutive spirit in Renaissance magic and alchemy, first introduced by Paracelsus in the 16th century and later adopted by more recent authors including those of modern fantasy literature. Its characte ...

, the most popular Linux desktops. There are also graphical GnuPG front-ends, for example Seahorse for GNOME and

KGPG KGpg is a graphical frontend to GnuPG for KDE, which includes a key management window and an editor. Users can easily create cryptographic keys, and write, encrypt, decrypt, sign, or verify messages. Through integration with the Konqueror ...

and

Kleopatra Kleopatra is a non-English spelling of Cleopatra. It may also refer to: * Kleopatra (singer) (born 1963), a Greek singer * 216 Kleopatra, a trinary asteroid orbiting in the asteroid belt * ''Kleopatra'' (opera), a Danish-language opera by August ...

for KDE. GPGTools provides a number of front-ends for OS integration of encryption and key management as well as GnuPG installations via Installer packages for macOS. GPG Suite installs all related OpenPGP applications (GPG Keychain), plugins (

GPG Mail GPG Mail is a Commercial software, commercial extension for Mail (Apple), Apple Mail which comes as part of GPG Suite, a software collection that provides easy access to a collection of tools designed to secure your communications and encrypt fil ...

) and dependencies (MacGPG), along with GPG Services (integration into macOS Services menu) to use GnuPG based encryption. Instant messaging applications such as

Psi Psi, PSI or Ψ may refer to: Alphabetic letters * Psi (Greek) (Ψ, ψ), the 23rd letter of the Greek alphabet * Psi (Cyrillic) (Ѱ, ѱ), letter of the early Cyrillic alphabet, adopted from Greek Arts and entertainment * "Psi" as an abbreviation ...

and Fire can automatically secure messages when GnuPG is installed and configured. Web-based software such as

Horde Horde may refer to: History * Orda (organization), a historic sociopolitical and military structure in steppe nomad cultures such as the Turks and Mongols ** Golden Horde, a Turkic-Mongol state established in the 1240s ** Wings of the Golden Hord ...

also makes use of it. The cross-platform

extension Extension, extend or extended may refer to: Mathematics Logic or set theory * Axiom of extensionality * Extensible cardinal * Extension (model theory) * Extension (predicate logic), the set of tuples of values that satisfy the predicate * E ...

Enigmail Enigmail is a data encryption and decryption extension for Mozilla Thunderbird and the Postbox that provides OpenPGP public key e-mail encryption and signing. Enigmail works under Microsoft Windows, Unix-like, and Mac OS X operating systems. Enigm ...

provides GnuPG support for Mozilla Thunderbird and SeaMonkey. Similarly, Enigform provides GnuPG support for

Mozilla Firefox Mozilla Firefox, or simply Firefox, is a free and open-source web browser developed by the Mozilla Foundation and its subsidiary, the Mozilla Corporation. It uses the Gecko rendering engine to display web pages, which implements current and a ...

. FireGPG was discontinued June 7, 2010. In 2005, g10 Code GmbH and Intevation GmbH released

Gpg4win Gpg4win is an email and file encryption package for most versions of Microsoft Windows and Microsoft Outlook, which utilises the GnuPG framework for symmetric and public-key cryptography, such as data encryption, digital signatures, hash calc ...

, a software suite that includes GnuPG for Windows, 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.

Vulnerabilities

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, since 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 A false positive is an error in binary classification in which a test result incorrectly indicates the presence of a condition (such as a disease when the disease is not present), while a false negative is the opposite error, where the test result ...

, 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. In June 2017, a vulnerability (CVE-2017-7526) was discovered within

by Bernstein, Breitner and others: a library used by GnuPG, which enabled a full key recovery for RSA-1024 and about more than 1/8th of RSA-2048 keys. This side-channel attack exploits the fact that

used a sliding windows method for exponentiation which leads to the leakage of exponent bits and to full key recovery. Again, an updated version of GnuPG was made available at the time of the announcement. In October 2017, the

ROCA vulnerability The ROCA vulnerability is a cryptographic weakness that allows the private key of a key pair to be recovered from the public key in keys generated by devices with the vulnerability. "ROCA" is an acronym for "Return of Coppersmith's attack". Th ...

was announced that affects RSA keys generated by YubiKey 4 tokens, which often are used with PGP/GPG. Many published PGP keys were found to be susceptible.The Return of Coppersmith's Attack: Practical Factorization of Widely Used RSA Moduli
, Matus Nemec, Marek Sys, Petr Svenda, Dusan Klinec,Vashek Matyas, November 2017 Around June 2018, the

SigSpoof SigSpoof () is a family of security vulnerabilities that affected the software package GNU Privacy Guard ("GnuPG") since version 0.2.2, that was released in 1998. Several other software packages that make use of GnuPG were also affected, such ...

attacks were announced. These allowed an attacker to convincingly spoof digital signatures. In January 2021, Libgcrypt 1.9.0 was released, which was found to contain a severe bug that was simple to exploit. A fix was released 10 days later in Libgcrypt 1.9.1.

Notes

References

External links

*
A Short History of the GNU Privacy Guard
written by Werner Koch, published on GnuPG's 10th birthday {{DEFAULTSORT:Gnu Privacy Guard 1999 software Cross-platform software Cryptographic software Free security software Privacy Guard Linux security software OpenPGP Privacy software