Pretty Good Privacy (PGP) is an encryption program that provides cryptographic privacy and authentication for data communication. PGP is used for signing, encrypting, and decrypting texts, e-mails, files, directories, and whole disk partitions and to increase the security of e-mail communications. Phil Zimmermann developed PGP in 1991.
The PGP software follows the OpenPGP standard in the now historical version . The software has not been kept up to date with developments in OpenPGP standardization. While the product is still being sold, its development appears to have stalled sometime around 2010: The current user's guide of "PGP Encryption Desktop for Windows" only mentions RSA and Diffie-Hellman key material, and lacks any mention of ECC cryptography (which has been introduced to OpenPGP in 2012 by ). The product also has no support for the updated formats in .
Modern versions of PGP are interoperable with GnuPG and other OpenPGP-compliant systems, when using cryptographic algorithms that both sides of a communication can handle. This algorithmic intersection has been shrinking with time.
Design Most aspects of PGP design apply more broadly to OpenPGP and are described at .
Security quality To the best of publicly available information, there is no known method which will allow a person or group to break PGP encryption by cryptographic or computational means. Indeed, in 1995, cryptographer Bruce Schneier characterized an early version as being "the closest you're likely to get to military-grade encryption". Early versions of PGP have been found to have theoretical vulnerabilities and so current versions are recommended. In addition to protecting data in transit over a network, PGP encryption can also be used to protect data in long-term data storage such as disk files. These long-term storage options are also known as data at rest, i.e. data stored, not in transit.
The cryptographic security of PGP encryption depends on the assumption that the algorithms used are unbreakable by direct cryptanalysis with current equipment and techniques.
In the original version, the RSA algorithm was used to encrypt session keys. RSA's security depends upon the one-way function nature of mathematical integer factoring. Similarly, the symmetric key algorithm used in PGP version 2 was IDEA, which might at some point in the future be found to have previously undetected cryptanalytic flaws. Specific instances of current PGP or IDEA insecurities (if they exist) are not publicly known. As current versions of PGP have added additional encryption algorithms, their cryptographic vulnerability varies with the algorithm used. However, none of the algorithms in current use are publicly known to have cryptanalytic weaknesses.
New versions of PGP are released periodically and vulnerabilities fixed by developers as they come to light. Any agency wanting to read PGP messages would probably use easier means than standard cryptanalysis, e.g. rubber-hose cryptanalysis or black-bag cryptanalysis (e.g. installing some form of trojan horse or keystroke logging software or hardware on the target computer to capture encrypted keyrings and their passwords). The FBI has already used this attack against PGP in its investigations. However, any such vulnerabilities apply not just to PGP but to any conventional encryption software.
In 2003, an incident involving seized Psion PDAs belonging to members of the Red Brigade indicated that neither the Italian police nor the FBI were able to decrypt PGP-encrypted files stored on them.
A second incident in December 2006, (see In re Boucher), involving US customs agents who seized a laptop PC that allegedly contained child pornography, indicates that US government agencies find it "nearly impossible" to access PGP-encrypted files. Additionally, a magistrate judge ruling on the case in November 2007 has stated that forcing the suspect to reveal his PGP passphrase would violate his Fifth Amendment rights i.e. a suspect's constitutional right not to incriminate himself. The Fifth Amendment issue was opened again as the government appealed the case, after which a federal district judge ordered the defendant to provide the key.
Evidence suggests that , British police investigators are unable to break PGP, so instead have resorted to using RIPA legislation to demand the passwords/keys. In November 2009 a British citizen was convicted under RIPA legislation and jailed for nine months for refusing to provide police investigators with encryption keys to PGP-encrypted files.
History
Early history Phil Zimmermann created the first version of PGP encryption in 1991. The name, "Pretty Good Privacy" was inspired by the name of a grocery store, "Ralph's Pretty Good Grocery", featured in radio host Garrison Keillor's fictional town, Lake Wobegon. This first version included a symmetric-key algorithm that Zimmermann had designed himself, named BassOmatic after a Saturday Night Live sketch. Zimmermann had been a long-time anti-nuclear activist, and created PGP encryption so that similarly inclined people might securely use BBSs and securely store messages and files. No license fee was required for its non-commercial use, and the complete source code was included with all copies.
In a posting of June 5, 2001, entitled "PGP Marks 10th Anniversary", Zimmermann describes the circumstances surrounding his release of PGP:
PGP found its way onto the Internet and rapidly acquired a considerable following around the world. Users and supporters included dissidents in totalitarian countries (some affecting letters to Zimmermann have been published, some of which have been included in testimony before the US Congress), civil libertarians in other parts of the world (see Zimmermann's published testimony in various hearings), and the 'free communications' activists who called themselves cypherpunks (who provided both publicity and distribution); decades later, CryptoParty activists did much the same via Twitter.
Criminal investigation Shortly after its release, PGP encryption found its way outside the United States, and in February 1993 Zimmermann became the formal target of a criminal investigation by the US Government for "munitions export without a license". At the time, cryptosystems using keys larger than 40 bits were considered munitions within the definition of the US export regulations; PGP has never used keys smaller than 128 bits, so it qualified at that time. Penalties for violation, if found guilty, were substantial. After several years, the investigation of Zimmermann was closed without filing criminal charges against him or anyone else in 1996. – page also contains NPR morning radio recording on this matter
Zimmermann challenged these regulations in an imaginative way. In 1995, he published the entire source code of PGP in a hardback book, via MIT Press, which was distributed and sold widely. Anybody wishing to build their own copy of PGP could cut off the covers, separate the pages, and scan them using an OCR program (or conceivably enter it as a type-in program if OCR software was not available), creating a set of source code text files. One could then build the application using the freely available GNU Compiler Collection. PGP would thus be available anywhere in the world. The claimed principle was simple: export of munitions—guns, bombs, planes, and software—was (and remains) restricted; but the export of books is protected by the First Amendment. The question was never tested in court with respect to PGP. In cases addressing other encryption software, however, two federal appeals courts have established the rule that cryptographic software source code is speech protected by the First Amendment (the Ninth Circuit Court of Appeals in the Bernstein case and the Sixth Circuit Court of Appeals in the Junger case).
US export regulations regarding cryptography remain in force, but were liberalized substantially throughout the late 1990s. Since 2000, compliance with the regulations is also much easier. PGP encryption no longer meets the definition of a non-exportable weapon, and can be exported internationally except to seven specific countries and a list of named groups and individuals (with whom substantially all US trade is prohibited under various US export controls).
PGP 3 and founding of PGP Inc. During this turmoil, Zimmermann's team worked on a new version of PGP encryption called PGP 3. This new version was to have considerable security improvements, including a new certificate structure that fixed small security flaws in the PGP 2.x certificates as well as permitting a certificate to include separate keys for signing and encryption. Furthermore, the experience with patent and export problems led them to eschew patents entirely. PGP 3 introduced the use of the CAST-128 (a.k.a. CAST5) symmetric key algorithm, and the DSA and ElGamal asymmetric key algorithms, all of which were unencumbered by patents.
After the Federal criminal investigation ended in 1996, Zimmermann and his team started a company to produce new versions of PGP encryption. They merged with Viacrypt (to whom Zimmermann had sold commercial rights and who had licensed RSA directly from RSADSI), which then changed its name to PGP Incorporated. The newly combined Viacrypt/PGP team started work on new versions of PGP encryption based on the PGP 3 system. Unlike PGP 2, which was an exclusively command line program, PGP 3 was designed from the start as a software library allowing users to work from a command line or inside a GUI environment. The original agreement between Viacrypt and the Zimmermann team had been that Viacrypt would have even-numbered versions and Zimmermann odd-numbered versions. Viacrypt, thus, created a new version (based on PGP 2) that they called PGP 4. To remove confusion about how it could be that PGP 3 was the successor to PGP 4, PGP 3 was renamed and released as PGP 5 in May 1997.
Network Associates acquisition In December 1997, PGP Inc. was acquired by Network Associates, Inc. ("NAI"). Zimmermann and the PGP team became NAI employees. NAI was the first company to have a legal export strategy by publishing source code. Under NAI, the PGP team added disk encryption, desktop firewalls, intrusion detection, and IPsec VPNs to the PGP family. After the export regulation liberalizations of 2000 which no longer required publishing of source, NAI stopped releasing source code.
Asset split In early 2001, Zimmermann left NAI. He served as Chief Cryptographer for Hush Communications, who provide an OpenPGP-based e-mail service, Hushmail. He has also worked with Veridis and other companies. In October 2001, NAI announced that its PGP assets were for sale and that it was suspending further development of PGP encryption. The only remaining asset kept was the PGP E-Business Server (the original PGP Commandline version). In February 2002, NAI canceled all support for PGP products, with the exception of the renamed commandline product.
McAfee NAI, now known as McAfee, continued to sell and support the commandline product under the name McAfee E-Business Server until 2013. In 2010, Intel Corporation acquired McAfee. In 2013, the McAfee E-Business Server was transferred to Software Diversified Services (SDS), which now sells, supports, and develops it under the name SDS E-Business Server.
For the enterprise, Townsend Security currently offers a commercial version of PGP for the IBM i and IBM z mainframe platforms. Townsend Security partnered with Network Associates in 2000 to create a compatible version of PGP for the IBM i platform. Townsend Security again ported PGP in 2008, this time to the IBM z mainframe. This version of PGP relies on a free z/OS encryption facility, which utilizes hardware acceleration. SDS also offers a commercial version of PGP (SDS E-Business Server) for the IBM z mainframe.
PGP Corporation