Rambutan is a family of

encryption In cryptography, encryption is the process of encoding information. This process converts the original representation of the information, known as plaintext, into an alternative form known as ciphertext. Ideally, only authorized parties can decip ...

technologies designed by the

Communications-Electronics Security Group Government Communications Headquarters, commonly known as GCHQ, is an intelligence and security organisation responsible for providing signals intelligence (SIGINT) and information assurance (IA) to the government and armed forces of the Un ...

(CESG), the technical division of the United Kingdom government's secret communications agency,

GCHQ Government Communications Headquarters, commonly known as GCHQ, is an intelligence and security organisation responsible for providing signals intelligence (SIGINT) and information assurance (IA) to the government and armed forces of the Unit ...

. It includes a range of encryption products designed by CESG for use in handling confidential (not secret) communications between parts of the British government, government agencies, and related bodies such as

NHS Trust An NHS trust is an organisational unit within the National Health Services of England and Wales, generally serving either a geographical area or a specialised function (such as an ambulance service). In any particular location there may be several ...

s. Unlike CESG's Red Pike system, Rambutan is not available as software: it is distributed only as a self-contained electronic device (an

ASIC An application-specific integrated circuit (ASIC ) is an integrated circuit (IC) chip customized for a particular use, rather than intended for general-purpose use, such as a chip designed to run in a digital voice recorder or a high-efficien ...

) which implements the entire cryptosystem and handles the related key distribution and storage tasks."The use of encryption and related services with the NHSnet"
report by Zergo Ltd. Rambutan is not sold outside the government sector.Schneier, Bruce ''Applied Cryptography'' (2nd ed), John Wiley & Sons, 1996 Technical details of the Rambutan algorithm are secret. Security researcher

Bruce Schneier Bruce Schneier (; born January 15, 1963) is an American cryptographer, computer security professional, privacy specialist, and writer. Schneier is a Lecturer in Public Policy at the Harvard Kennedy School and a Fellow at the Berkman Klein Cente ...

describes it as being a

stream cipher stream cipher is a symmetric key cipher where plaintext digits are combined with a pseudorandom cipher digit stream (keystream). In a stream cipher, each plaintext digit is encrypted one at a time with the corresponding digit of the keystream ...

(

linear-feedback shift register In computing, a linear-feedback shift register (LFSR) is a shift register whose input bit is a linear function of its previous state. The most commonly used linear function of single bits is exclusive-or (XOR). Thus, an LFSR is most often a sh ...

) based cryptosystem with 5

shift register A shift register is a type of digital circuit using a cascade of flip-flops where the output of one flip-flop is connected to the input of the next. They share a single clock signal, which causes the data stored in the system to shift from one loc ...

s each of around 80 bits, and a

key size In cryptography, key size, key length, or key space refer to the number of bits in a key used by a cryptographic algorithm (such as a cipher). Key length defines the upper-bound on an algorithm's security (i.e. a logarithmic measure of the fastest ...

of 112 bits. RAMBUTAN-I communications chips (which implement a secure

X.25 X.25 is an ITU-T standard protocol suite for packet-switched data communication in wide area networks (WAN). It was originally defined by the International Telegraph and Telephone Consultative Committee (CCITT, now ITU-T) in a series of drafts ...

based communications system) are made by approved contractors

Racal Racal Electronics plc was a British electronics company that was founded in 1950. Listed on the London Stock Exchange and once a constituent of the FTSE 100 Index, Racal was a diversified company, offering products including voice loggers and ...

and Baltimore Technologies/Zergo Ltd.Racal Rambutan SAFE X25 and Rambutan SAFE 2M product descriptions

CESG later specified RAMBUTAN-II, an enhanced system with backward compatibility with existing RAMBUTAN-I infrastructure."RAMBUTAN-II"
, CESG website, URL retrieved 17 December 2006 The RAMBUTAN-II chip is a 64-pin quad ceramic pack chip, which implements the electronic codebook, cipher block chaining, and output feedback operating modes (each in 64 bits) and the cipher feedback mode in 1 or 8 bits."RAMBUTAN II cryptographic chip"
, CESG brochure Schneier suggests that these modes may indicate Rambutan is a

block cipher In cryptography, a block cipher is a deterministic algorithm operating on fixed-length groups of bits, called ''blocks''. Block ciphers are specified cryptographic primitive, elementary components in the design of many cryptographic protocols and ...

rather than a stream. The three 64 bit modes operate at 88 megabits/second. Rambutan operates in three modes: ECB, CBC, and 8 bit CFB.

References

Cryptographic hardware Stream ciphers {{crypto-stub