RC2
Encyclopedia
In cryptography
, RC2 is a block cipher
designed by Ron Rivest
in 1987. "RC" stands for "Ron's Code" or "Rivest Cipher"; other ciphers designed by Rivest include RC4, RC5
and RC6
.
The development of RC2 was sponsored by Lotus
, who were seeking a custom cipher
that, after evaluation by the NSA, could be exported as part of their Lotus Notes
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
was treated favourably under US export regulations for cryptography
.
Initially, the details of the algorithm were kept secret — proprietary to RSA Security
— but on 29th January, 1996, source code for RC2 was anonymously posted to the Internet on the Usenet
forum, sci.crypt. Mentions of CodeView
and SoftICE
(popular debuggers
) suggest that it had been reverse engineered
. A similar disclosure had occurred earlier with RC4.
RC2 is a 64-bit block
cipher with a variable size key
. Its 18 rounds are arranged as a source-heavy 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
using 234 chosen plaintexts (Kelsey et al., 1997).
Cryptography
Cryptography is the practice and study of techniques for secure communication in the presence of third parties...
, RC2 is a block cipher
Block cipher
In cryptography, a block cipher is a symmetric key cipher operating on fixed-length groups of bits, called blocks, with an unvarying transformation. A block cipher encryption algorithm might take a 128-bit block of plaintext as input, and output a corresponding 128-bit block of ciphertext...
designed by Ron Rivest
Ron Rivest
Ronald Linn Rivest is a cryptographer. He is the Andrew and Erna Viterbi Professor of Computer Science at MIT's Department of Electrical Engineering and Computer Science and a member of MIT's Computer Science and Artificial Intelligence Laboratory...
in 1987. "RC" stands for "Ron's Code" or "Rivest Cipher"; other ciphers designed by Rivest include RC4, RC5
RC5
In cryptography, RC5 is a block cipher notable for its simplicity. Designed by Ronald Rivest in 1994, RC stands for "Rivest Cipher", or alternatively, "Ron's Code"...
and RC6
RC6
In cryptography, RC6 is a symmetric key block cipher derived from RC5. It was designed by Ron Rivest, Matt Robshaw, Ray Sidney, and Yiqun Lisa Yin to meet the requirements of the Advanced Encryption Standard competition. The algorithm was one of the five finalists, and was also submitted to the...
.
The development of RC2 was sponsored by Lotus
Lotus Software
Lotus Software is a software company with headquarters in Westford, Massachusetts...
, who were seeking a custom cipher
Cipher
In cryptography, a cipher 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. In non-technical usage, a “cipher” is the same thing as a “code”; however, the concepts...
that, after evaluation by the NSA, could be exported as part of their Lotus Notes
Lotus Notes
Lotus Notes is the client of a collaborative platform originally created by Lotus Development Corp. in 1989. In 1995 Lotus was acquired by IBM and became known as the Lotus Development division of IBM and is now part of the IBM Software Group...
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
Key size
In cryptography, key size or key length is the size measured in bits of the key used in a cryptographic algorithm . An algorithm's key length is distinct from its cryptographic security, which is a logarithmic measure of the fastest known computational attack on the algorithm, also measured in bits...
was treated favourably under US export regulations for cryptography
Export of cryptography
The export of cryptography in the United States is the transfer from the United States to another country of devices and technology related to cryptography....
.
Initially, the details of the algorithm were kept secret — proprietary to RSA Security
RSA Security
RSA, the security division of EMC Corporation, is headquartered in Bedford, Massachusetts, United States, and maintains offices in Australia, Ireland, Israel, the United Kingdom, Singapore, India, China, Hong Kong and Japan....
— but on 29th January, 1996, source code for RC2 was anonymously posted to the Internet on the Usenet
Usenet
Usenet is a worldwide distributed Internet discussion system. It developed from the general purpose UUCP architecture of the same name.Duke University graduate students Tom Truscott and Jim Ellis conceived the idea in 1979 and it was established in 1980...
forum, sci.crypt. Mentions of CodeView
CodeView
CodeView was 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 number of other Microsoft language products...
and SoftICE
SoftICE
SoftICE is a kernel mode debugger for Microsoft Windows. Crucially, it is designed to run underneath Windows such that the operating system is unaware of its presence. Unlike an application debugger, SoftICE is capable of suspending all operations in Windows when instructed...
(popular debuggers
Debugger
A debugger or debugging tool is a computer program that is used to test and debug other programs . The code to be examined might alternatively be running on an instruction set simulator , a technique that allows great power in its ability to halt when specific conditions are encountered but which...
) suggest that it had been reverse engineered
Reverse engineering
Reverse engineering is the process of discovering the technological principles of a device, object, or system through analysis of its structure, function, and operation...
. A similar disclosure had occurred earlier with RC4.
RC2 is a 64-bit block
Block size (cryptography)
In modern cryptography, symmetric key ciphers are generally divided into stream ciphers and block ciphers. Block ciphers operate on a fixed length string of bits. The length of this bit string is the block size...
cipher with a variable size key
Key (cryptography)
In cryptography, a key is a piece of information that determines the functional output of a cryptographic algorithm or cipher. Without a key, the algorithm would produce no useful result. In encryption, a key specifies the particular transformation of plaintext into ciphertext, or vice versa...
. Its 18 rounds are arranged as a source-heavy 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
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 keys is known to the attacker...
using 234 chosen plaintexts (Kelsey et al., 1997).
Sources
- Steven LevySteven LevySteven Levy is an American journalist who has written several books on computers, technology, cryptography, the Internet, cybersecurity, and privacy.-Career:...
, Crypto: How the Code Rebels Beat the Government — Saving Privacy in the Digital AgeCrypto: How the Code Rebels Beat the Government Saving Privacy in the Digital AgeCrypto: How the Code Rebels Beat the Government Saving Privacy in the Digital Age is a book written by Steven Levy about cryptography, and was published in 2001. Levy details the emergence of public key cryptography, digital signatures and the struggle between the NSA and the cypherpunks. The...
, ISBN 0-14-024432-8, 2001.
External links
- RFC 2268 - A Description of the RC2(r) Encryption Algorithm
- RSA FAQ: What is RC2?
- sci.crypt posting revealing the RC2 algorithm