The ISAAC algorithm has similarities with RC4. It uses an array of 256 four-octet integers as the internal state, writing the results to another 256 four-octet integer array, from which they are read one at a time until empty, at which point they are recomputed. The computation consists of altering i-element with (i⊕128)-element, two elements of the state array 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 very fast on 32-bit computers.
Cryptanalysisedit
Cryptanalysis has been undertaken by Marina Pudovkina (2001).[4] 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 instead of . This result has had no practical impact on the security of ISAAC.[5]
In 2006 Jean-Philippe Aumasson discovered several sets of weak states.[6] 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. It is not clear if an attacker can tell from just the output whether the generator is in one of these weak states or not. He also shows that a previous attack[7] is flawed, since the Paul-Preneel attack is based on an erroneous algorithm rather than the real ISAAC. An improved version of ISAAC is proposed, called ISAAC+.[5]
Usage outside cryptographyedit
Many implementations of ISAAC are so fast that they can compete with other high speed PRNGs, even with those designed primarily for speed not for security. Only a few other generators of such high quality and speed exist in usage.[citation needed] ISAAC is used in the Unix tool shred to securely overwrite data.[8] Also ISAAC algorithm is implemented in Java Apache Commons Math library.[9]
Referencesedit
^Robert J. Jenkins Jr., ISAAC. Fast Software Encryption 1996, pp. 41–49.
^. Archived from the original on 2022-02-16. Retrieved 2022-02-16.
External linksedit
Official ISAAC website
Multiple ISAAC implementations at Rosetta Code
Math::Random::ISAAC, a Perl module implementation of the algorithm
isaac.js, a JavaScript implementation
January 01, 1970
isaac, cipher, isaac, indirection, shift, accumulate, count, cryptographically, secure, pseudorandom, number, generator, stream, cipher, designed, robert, jenkins, 1993, reference, implementation, source, code, dedicated, public, domain, developed, tests, brea. ISAAC indirection shift accumulate add and count is a cryptographically secure pseudorandom number generator and a stream cipher designed by Robert J Jenkins Jr in 1993 1 The reference implementation source code was dedicated to the public domain 2 I developed tests to break a generator and I developed the generator to pass the tests The generator is ISAAC 3 Contents 1 Operation 2 Cryptanalysis 3 Usage outside cryptography 4 References 5 External linksOperation editThe ISAAC algorithm has similarities with RC4 It uses an array of 256 four octet integers as the internal state writing the results to another 256 four octet integer array from which they are read one at a time until empty at which point they are recomputed The computation consists of altering i element with i 128 element two elements of the state array 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 very fast on 32 bit computers Cryptanalysis editCryptanalysis has been undertaken by Marina Pudovkina 2001 4 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 10 1240 displaystyle 4 67 times 10 1240 nbsp instead of 10 2466 displaystyle 10 2466 nbsp This result has had no practical impact on the security of ISAAC 5 In 2006 Jean Philippe Aumasson discovered several sets of weak states 6 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 It is not clear if an attacker can tell from just the output whether the generator is in one of these weak states or not He also shows that a previous attack 7 is flawed since the Paul Preneel attack is based on an erroneous algorithm rather than the real ISAAC An improved version of ISAAC is proposed called ISAAC 5 Usage outside cryptography editMany implementations of ISAAC are so fast that they can compete with other high speed PRNGs even with those designed primarily for speed not for security Only a few other generators of such high quality and speed exist in usage citation needed ISAAC is used in the Unix tool shred to securely overwrite data 8 Also ISAAC algorithm is implemented in Java Apache Commons Math library 9 References edit Robert J Jenkins Jr ISAAC Fast Software Encryption 1996 pp 41 49 The ISAAC Cipher Jenkins Bob 2023 03 17 Tests for Random Number Generators Marina Pudovkina A known plaintext attack on the ISAAC keystream generator 2001 Cryptology ePrint Archive Report 2001 049 1 a b On the pseudo random generator ISAAC PDF Cryptology ePrint Archive Retrieved 21 August 2016 Jean Philippe Aumasson On the pseudo random generator ISAAC Cryptology ePrint archive report 2006 438 2006 Souradyuti Paul Bart Preneel On the In security of Stream Ciphers Based on Arrays and Modular Addition Asiacrypt 2006 GNU coreutils git Apache Commons Math reference Archived from the original on 2022 02 16 Retrieved 2022 02 16 External links editOfficial ISAAC website Multiple ISAAC implementations at Rosetta Code Pascal Delphi port Math Random ISAAC a Perl module implementation of the algorithm isaac js a JavaScript implementation Retrieved from https en wikipedia org w index php title ISAAC cipher amp oldid 1180511056, wikipedia, wiki, book, books, library,
