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Encyclopedia > ISAAC (cipher)

ISAAC is a pseudorandom number generator designed by Bob Jenkins (1996) to be cryptographically secure. The name is an acronym for Indirection, Shift, Accumulate, Add, and Count.[1] A pseudorandom number generator (PRNG) is an algorithm that generates a sequence of numbers which are not truly random. ... Bob Jenkins (born September 4, 1947 in Liberty, Indiana) is a television and radio sports announcer best known for his work at ABC and ESPN calling NASCAR and IndyCar telecasts. ... 1996 (MCMXCVI) was a leap year starting on Monday of the Gregorian calendar, and was designated the International Year for the Eradication of Poverty. ... A cryptographically secure pseudo-random number generator (CSPRNG) is a pseudo-random number generator (PRNG) with properties that make it suitable for use in cryptography. ... It has been suggested that this article or section be merged with Backronym and Apronym (Discuss) Acronyms and initialisms are abbreviations, such as NATO, laser, and ABC, written as the initial letter or letters of words, and pronounced on the basis of this abbreviated written form. ...

Contents

Operation

The ISAAC algorithm has similarities to RC4. It uses an array of 256 4-byte integers (called mm) as the internal state, writing the results to another 256-integer array, from which they are read one at a time until empty, at which point they are recomputed. The computation consists of altering mm[i] with mm[i^128], two elements of mm found by indirection, an accumulator, and a counter, for all values of i from 0 to 255. Since it only takes about 19 32-bit operations for each 32-bit output word, it is extremely fast on 32-bit computers. In mathematics, computing, linguistics and related disciplines, an algorithm is a procedure (a finite set of well-defined instructions) for accomplishing some task which, given an initial state, will terminate in a defined end-state. ... In cryptography, RC4 (also known as ARC4 or ARCFOUR) is the most widely-used software stream cipher and is used in popular protocols such as Secure Sockets Layer (SSL) (to protect Internet traffic) and WEP (to secure wireless networks). ... In computer programming, a group of homogeneous elements of a specific data type is known as an array, one of the simplest data structures. ... In computer science, the term integer is used to refer to any data type which can represent some subset of the mathematical integers. ...


Cryptanalysis

Cryptanalysis has been undertaken by Marina Pudovkina (2001)[2]. Her attack can recover the initial state with a complexity that is approximated to be less than the time needed for searching through the square root of all possible initial states. In practice this means that the attack needs 4.67 times 10^{1240} instead of 102466. This result has had no practical impact on the security of ISAAC. As always with cryptographic primitives, future improvements, or another attack, might. Cryptanalysis (from the Greek kryptós, hidden, and analýein, to loosen or to untie) is the study of methods for obtaining the meaning of encrypted information, without access to the secret information which is normally required to do so. ... This article is about the year 2001. ... The German Lorenz cipher machine, used in World War II for encryption of very high-level general staff messages Cryptography (or cryptology; derived from Greek κρυπτός kryptós hidden, and γράφειν gráfein to write) is the study of message secrecy. ...


In 2006 Jean-Philippe Aumasson discovered several sets of weak states[3]. The fourth presented (and smallest) set of weak states leads to a highly biased output for the first round of ISAAC and allows the derivation of the internal state, similar to a weakness in RC4. He also shows that a previous attack[4] is not relevant, since based on an erroneous algorithm. An improved version of ISAAC is proposed, called ISAAC+. 2006 (MMVI) is a common year starting on Sunday of the Gregorian calendar. ... In cryptography, RC4 (also known as ARC4 or ARCFOUR) is the most widely-used software stream cipher and is used in popular protocols such as Secure Sockets Layer (SSL) (to protect Internet traffic) and WEP (to secure wireless networks). ...


References

  1. ^ Robert J. Jenkins Jr., ISAAC. Fast Software Encryption 1996, pp41–49.
  2. ^ Marina Pudovkina, A known plaintext attack on the ISAAC keystream generator, 2001, Cryptology ePrint Archive: Report 2001/049, [1].
  3. ^ Jean-Philippe Aumasson, On the pseudo-random generator ISAAC.Cryptology ePrint archive, report 2006/438, 2006.
  4. ^ Souradyuti Paul, Bart Preneel, On the (In)security of Stream Ciphers Based on Arrays and Modular Addition.Asiacrypt 2006.

External links

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Theory: Shift register | LFSR | NLFSR | Shrinking generator   Standardization: eSTREAM
Cryptography
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History of cryptography | Cryptanalysis | Cryptography portal | Topics in cryptography
Symmetric-key algorithm | Block cipher | Stream cipher | Public-key cryptography | Cryptographic hash function | Message authentication code | Random numbers

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ISAAC (cipher) - Wikipedia, the free encyclopedia (328 words)
ISAAC is a pseudorandom number generator designed by Bob Jenkins (1996) to be cryptographically secure.
The fourth presented (and smallest) set of weak states leads to a highly biased output for the first round of ISAAC and allows the derivation of the internal state, similar to a weakness in RC4.
An improved version of ISAAC is proposed, called ISAAC+.
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