A secure telephone is a

telephone A telephone is a telecommunications device that permits two or more users to conduct a conversation when they are too far apart to be easily heard directly. A telephone converts sound, typically and most efficiently the human voice, into e ...

that provides voice security in the form of

end-to-end encryption End-to-end encryption (E2EE) is a system of communication where only the communicating users can read the messages. In principle, it prevents potential eavesdroppers – including telecom providers, Internet providers, malicious actors, and even ...

for the telephone call, and in some cases also the mutual authentication of the call parties, protecting them against a

man-in-the-middle attack In cryptography and computer security, a man-in-the-middle, monster-in-the-middle, machine-in-the-middle, monkey-in-the-middle, meddler-in-the-middle, manipulator-in-the-middle (MITM), person-in-the-middle (PITM) or adversary-in-the-middle (AiTM) ...

. Concerns about massive growth of

telephone tapping Telephone tapping (also wire tapping or wiretapping in American English) is the monitoring of telephone and Internet-based conversations by a third party, often by covert means. The wire tap received its name because, historically, the monitorin ...

incidents led to growing demand for secure telephones. The practical availability of secure telephones is restricted by several factors; notably politics, export issues, incompatibility between different products (the devices on each side of the call have to use the same protocol), and high (though recently decreasing) price of the devices.

Well-known products

The best-known product on the US government market is the

STU-III STU-III (Secure Telephone Unit - third generation) is a family of secure telephones introduced in 1987 by the NSA for use by the United States government, its contractors, and its allies. STU-III desk units look much like typical office telephone ...

family. However, this system has now been replaced by the

Secure Terminal Equipment Secure Terminal Equipment (STE) is the U.S. government's current (), encrypted telephone communications system for wired or "landline" communications. STE is designed to use ISDN telephone lines which offer higher speeds of up to 128 kbit/s ...

(STE) and SCIP standards which defines specifications for the design of equipment to secure both

data In the pursuit of knowledge, data (; ) is a collection of discrete values that convey information, describing quantity, quality, fact, statistics, other basic units of meaning, or simply sequences of symbols that may be further interpreted ...

and voice. The SCIP standard was developed by the

NSA The National Security Agency (NSA) is a national-level intelligence agency of the United States Department of Defense, under the authority of the Director of National Intelligence (DNI). The NSA is responsible for global monitoring, collecti ...

and the

US DOD The United States Department of Defense (DoD, USDOD or DOD) is an executive branch department of the federal government charged with coordinating and supervising all agencies and functions of the government directly related to national secur ...

to derive more

interoperability 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 ...

between secure communication equipment. A new family of standard secure phones has been developed based on Philip Zimmermann's VoIP encryption standard

ZRTP ZRTP (composed of Z and Real-time Transport Protocol) is a cryptographic key-agreement protocol to negotiate the keys for encryption between two end points in a Voice over IP (VoIP) phone telephony call based on the Real-time Transport Protocol. I ...

VoIP and direct connection phones

As the popularity of

VoIP Voice over Internet Protocol (VoIP), also called IP telephony, is a method and group of technologies for the delivery of voice communications and multimedia sessions over Internet Protocol (IP) networks, such as the Internet. The terms Internet t ...

grows, secure telephony is becoming more widely used. Many major hardware and software providers offer it as a standard feature at no extra cost. Examples include the

Gizmo5 Gizmo5 (formerly known as Gizmo Project and SIPphone) was a voice over IP communications network and a proprietary freeware soft phone for that network. On November 12, 2009, Google announced that it had acquired Gizmo5. On March 4, 2011, Google ...

and

Twinkle Twinkle may refer to: * Twinkling, the variation of brightness of distant objects People * Twinkle (singer) (1948–2015), born Lynn Annette Ripley, English singer-songwriter * Twinkle Khanna, Indian movie actress * Twinkle Bajpai, female conte ...

. Both of the former work with offerings from the founder of PGP,

Phil Zimmermann Philip R. Zimmermann (born 1954) is an American computer scientist and Cryptography, cryptographer. He is the creator of Pretty Good Privacy (PGP), the most widely used email encryption software in the world. He is also known for his work in VoI ...

, and his VoIP secure protocol,

. ZRTP is implemented in, amongst others,

Ripcord Networks Ripcord Networks was a voice and video cryptographic security company. Their headquarters was in San Mateo, California in the United States. Ripcord Networks was founded in 2003. Board members included Steve Wozniak, Apple Computer's co-founder ...

product SecurePC with up to NSA Suite B compliant Elliptic Curve math libraries. ZRTP is also being made available for mobile

GSM The Global System for Mobile Communications (GSM) is a standard developed by the European Telecommunications Standards Institute (ETSI) to describe the protocols for second-generation ( 2G) digital cellular networks used by mobile devices such as ...

CSD as a new standard for non-VoIP secure calls. The U.S.

National Security Agency The National Security Agency (NSA) is a national-level intelligence agency of the United States Department of Defense, under the authority of the Director of National Intelligence (DNI). The NSA is responsible for global monitoring, collecti ...

is developing a secure phone based on Google's Android called Fishbowl.

Historically significant products

Scrambler In telecommunications, a scrambler is a device that transposes or inverts signals or otherwise encodes a message at the sender's side to make the message unintelligible at a receiver not equipped with an appropriately set descrambling device. Wher ...

s were used to

secure voice Secure voice (alternatively secure speech or ciphony) is a term in cryptography for the encryption of voice communication over a range of communication types such as radio, telephone or IP. History The implementation of voice encryption date ...

traffic during

World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposin ...

, but were often intercepted and decoded due to scrambling's inherent insecurity. The first true secure telephone was

SIGSALY SIGSALY (also known as the X System, Project X, Ciphony I, and the Green Hornet) was a secure speech system used in World War II for the highest-level Allied communications. It pioneered a number of digital communications concepts, including the ...

, a massive device that weighed over 50 tons. The NSA, formed after World War II, developed a series of secure telephones, including the STU I, STU II and

, as well as

voice encryption Secure voice (alternatively secure speech or ciphony) is a term in cryptography for the encryption of voice communication over a range of communication types such as radio, telephone or IP. History The implementation of voice encryption date ...

devices for military telephones. In 1989 an Irish company called Intrepid developed one of the most advanced secure phones. Called Milcode, the phone was the first to implement

code-excited linear prediction Code-excited linear prediction (CELP) is a linear predictive speech coding algorithm originally proposed by Manfred R. Schroeder and Bishnu S. Atal in 1985. At the time, it provided significantly better quality than existing low bit-rate algori ...

(or CELP) which dramatically improved voice quality and user operability over previous LPC (Linear Predictive Coding) and LPC-10e versions. Milcode also boasted significantly higher levels of security than previous secure telephones. The base model offered a proprietary encryption algorithm with a key length of 512 bits, and a more advanced model with a key length of 1024 bits. Key exchange used a public key, based on Diffie-Hellman, as opposed to a plug-in datakey. A new key was generated for each phone call. Milcode was also able to encrypt fax and data and was electromagnetically shielded to NATO

TEMPEST Tempest is a synonym for a storm. '' The Tempest'' is a play by William Shakespeare. Tempest or The Tempest may also refer to: Arts and entertainment Films * ''The Tempest'' (1908 film), a British silent film * ''The Tempest'' (1911 film), a ...

standards. Other products of historical significance are

PGPfone PGPfone was a secure voice telephony system developed by Philip Zimmermann in 1995. The PGPfone protocol had little in common with Zimmermann's popular PGP email encryption package, except for the use of the name. It used ephemeral Diffie-Hel ...

and

Nautilus The nautilus (, ) is a pelagic marine mollusc of the cephalopod family Nautilidae. The nautilus is the sole extant family of the superfamily Nautilaceae and of its smaller but near equal suborder, Nautilina. It comprises six living species in t ...

(designed as a non-

key escrow Key escrow (also known as a "fair" cryptosystem) is an arrangement in which the keys needed to decrypt encrypted data are held in escrow so that, under certain circumstances, an authorized third party may gain access to those keys. These third pa ...

alternative to

Clipper A clipper was a type of mid-19th-century merchant sailing vessel, designed for speed. Clippers were generally narrow for their length, small by later 19th century standards, could carry limited bulk freight, and had a large total sail area. "C ...

, now officially discontinued, but still available on

SourceForge SourceForge is a web service that offers software consumers a centralized online location to control and manage open-source software projects and research business software. It provides source code repository hosting, bug tracking, mirrorin ...

), ''SpeakFreely'', and the security VoIP protocol wrapper

Zfone is software for secure voice communication over the Internet (VoIP), using the ZRTP protocol. It is created by Phil Zimmermann, the creator of the PGP encryption software. Zfone works on top of existing SIP- and RTP-programs, but should work w ...

developed by the creator of

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 ...

. Scrambling, generally using a form of

voice inversion Voice inversion scrambling is an analog method of obscuring the content of a transmission. It is sometimes used in public service radio, automobile racing, cordless telephones and the Family Radio Service. Without a descrambler, the transmission ma ...

, was available from electronic hobbyist kit suppliers and is common on FRS radios. Analog scrambling is still used, as some telecommunications circuits, such as HF links and telephone lines in the developing world, are of very low quality.

References

External links

Seminar on crypto phones by Zidu Wang
{{Refimprove, date=May 2021 Cryptographic hardware

Well-known products

VoIP and direct connection phones

Historically significant products

See also

References

External links