cryptography Cryptography, or cryptology (from "hidden, secret"; and ''graphein'', "to write", or ''-logy, -logia'', "study", respectively), is the practice and study of techniques for secure communication in the presence of Adversary (cryptography), ...

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

block cipher In cryptography, a block cipher is a deterministic algorithm that operates on fixed-length groups of bits, called ''blocks''. Block ciphers are the elementary building blocks of many cryptographic protocols. They are ubiquitous in the storage a ...

Ron Rivest Ronald Linn Rivest (; born May 6, 1947) is an American cryptographer and computer scientist whose work has spanned the fields of algorithms and combinatorics, cryptography, machine learning, and election integrity. He is an Institute Profess ...

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 In cryptography, RC5 is a symmetric-key block cipher notable for its simplicity. Designed by Ronald Rivest in 1994, ''RC'' stands for "Rivest Cipher", or alternatively, "Ron's Code" (compare RC2 and RC4). The Advanced Encryption Standard (AES) ...

, 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 i ...

that, after evaluation by the

NSA The National Security Agency (NSA) is an 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, collection, and proces ...

, could be exported as part of their

Lotus Notes HCL Notes (formerly Lotus Notes then IBM Notes) is a proprietary collaborative software platform for Unix ( AIX), IBM i, Windows, Linux, and macOS, sold by HCLTech. The client application is called Notes while the server component is branded ...

software. The NSA suggested a few 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 or key length refers 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 known a ...

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 trade name RSA, is an American computer security, computer and network security company with a focus on encryption and decryption standards. RSA was named after the initials of its co-founders, ...

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

Usenet Usenet (), a portmanteau of User's Network, is a worldwide distributed discussion system available on computers. It was developed from the general-purpose UUCP, Unix-to-Unix Copy (UUCP) dial-up network architecture. Tom Truscott and Jim Elli ...

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 num ...

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 oper ...

(popular

debugger A debugger is a computer program used to test and debug other programs (the "target" programs). Common features of debuggers include the ability to run or halt the target program using breakpoints, step through code line by line, and display ...

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 accompl ...

. 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 researc ...

, 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 ...

using 2³⁴

chosen plaintext Chosen or The Chosen may refer to: Books *The Chosen (Potok novel), ''The Chosen'' (Potok novel), a 1967 novel by Chaim Potok * ''The Chosen'', a 1997 novel by L. J. Smith (author), L. J. Smith *The Chosen (Pinto novel), ''The Chosen'' (Pinto nov ...

References

Bibliography

* * *

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