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 adv ...

, 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 elementary components in the design of many cryptographic protocols and are widely used to en ...

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 In ...

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, 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 ...

that, after evaluation 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, collec ...

, 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 Server may refer to: Computing *Server (computing), a computer program or a device that provide ...

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 4 (four) is a number, numeral and digit. It is the natural number following 3 and preceding 5. It is the smallest semiprime and composite number, and is considered unlucky in many East Asian cultures. In mathematics Four is the smallest ...

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 faste ...

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 and network security company with a focus on encryption and encryption standards. RSA was named after the initials of its co-founders, Ron Rive ...

— 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 wa ...

forum, sci.crypt. Mentions of

CodeView CodeView is a standalone debugger created by David Norris at Microsoft in 1985 as part of its development toolset. It originally shipped with Microsoft C 4.0 and later. It also shipped with Visual Basic for MS-DOS, Microsoft BASIC PDS, and a ...

and

SoftICE SoftICE is a kernel mode debugger for DOS and Windows up to Windows XP. It is designed to run underneath Windows, so that the operating system is unaware of its presence. Unlike an application debugger, SoftICE is capable of suspending all ...

(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 executi ...

s) suggest that it had been

reverse engineered Reverse engineering (also known as backwards engineering or back engineering) is a process or method through which one attempts to understand through deductive reasoning how a previously made device, process, system, or piece of software accompli ...

. 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, 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 ke ...

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