cryptography 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 ...

, RC2 (also known as ARC2) is a symmetric-key

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 ...

Ron Rivest Ronald Linn Rivest (; born May 6, 1947) is a cryptographer and an Institute Professor at MIT. He is a member of MIT's Department of Electrical Engineering and Computer Science (EECS) and a member of MIT's Computer Science and Artificial Int ...

in 1987. "RC" stands for "Ron's Code" or "Rivest Cipher"; other ciphers designed by Rivest include

RC4 In cryptography, RC4 (Rivest Cipher 4, also known as ARC4 or ARCFOUR, meaning Alleged RC4, see below) is a stream cipher. While it is remarkable for its simplicity and speed in software, multiple vulnerabilities have been discovered in RC4, ren ...

, RC5, and RC6. The development of RC2 was sponsored by

Lotus Lotus may refer to: Plants *Lotus (plant), various botanical taxa commonly known as lotus, particularly: ** ''Lotus'' (genus), a genus of terrestrial plants in the family Fabaceae **Lotus flower, a symbolically important aquatic Asian plant also ...

, who were seeking a custom

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 ...

that, after evaluation by the NSA, could be exported as part of their

Lotus Notes HCL Notes (formerly IBM Notes and Lotus Notes; see Branding below) and HCL Domino (formerly IBM Domino and Lotus Domino) are the client and server, respectively, of a collaborative client-server software platform formerly sold by IBM, now by HCL ...

software. The NSA suggested a couple of changes, which Rivest incorporated. After further negotiations, the cipher was approved for export in 1989. Along with RC4, RC2 with a 40-bit

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 fastes ...

was treated favourably under US export regulations for cryptography. Initially, the details of the algorithm were kept secret — proprietary to

RSA Security RSA Security LLC, formerly RSA Security, Inc. and doing business as RSA, is an American computer security, computer and network security company with a focus on encryption and encryption standards. RSA was named after the initials of its co-fo ...

— but on 29 January 1996, source code for RC2 was anonymously posted to the Internet on the

Usenet Usenet () is a worldwide distributed discussion system available on computers. It was developed from the general-purpose Unix-to-Unix Copy (UUCP) dial-up network architecture. Tom Truscott and Jim Ellis conceived the idea in 1979, and it was ...

forum, sci.crypt. Mentions of CodeView and SoftICE (popular

debugger A debugger or debugging tool is a computer program used to test and debug other programs (the "target" program). The main use of a debugger is to run the target program under controlled conditions that permit the programmer to track its execut ...

s) suggest that it had been reverse engineered. A similar disclosure had occurred earlier with RC4. In March 1998 Ron Rivest authored an RFC publicly describing RC2 himself. RC2 is a 64-bit block cipher with a variable size key. Its 18 rounds are arranged as a source-heavy unbalanced

Feistel network In cryptography, a Feistel cipher (also known as Luby–Rackoff block cipher) is a symmetric structure used in the construction of block ciphers, named after the German-born physicist and cryptographer Horst Feistel, who did pioneering research whi ...

, with 16 rounds of one type (''MIXING'') punctuated by two rounds of another type (''MASHING''). A MIXING round consists of four applications of the MIX transformation, as shown in the diagram. RC2 is vulnerable to a

related-key attack In cryptography, a related-key attack is any form of cryptanalysis where the attacker can observe the operation of a cipher under several different keys whose values are initially unknown, but where some mathematical relationship connecting the k ...

using 2³⁴

chosen plaintext A chosen-plaintext attack (CPA) is an attack model for cryptanalysis which presumes that the attacker can obtain the ciphertexts for arbitrary plaintexts.Ross Anderson, ''Security Engineering: A Guide to Building Dependable Distributed Systems'' ...

s (Kelsey et al., 1997).

Sources

References

* *

External links

* - A Description of the RC2(r) Encryption Algorithm
RSA FAQ: What is RC2?

sci.crypt posting revealing the RC2 algorithm
{{Cryptography navbox , block Broken block ciphers