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Encyclopedia > XTEA
XTEA
Two Feistel rounds (one "cycle") of XTEA
General
Designer(s) Roger Needham and David Wheeler
First published 1997
Derived from Tiny Encryption Algorithm (TEA)
Cipher(s) based on this design -
Algorithm detail
Block size(s) 64 bits
Key size(s) 128 bits
Structure Feistel network
Number of rounds variable; recommended 64 Feistel rounds; 32 "cycles"
Best cryptanalysis
A related-key differential attack can break 26 out of 64 rounds of XTEA, requiring 220.5 chosen plaintexts and a time complexity of 2115.15 (Ko et al, 2004).

In cryptography, XTEA (eXtended TEA) is a block cipher designed to correct weaknesses in TEA. The cipher's designers were David Wheeler and Roger Needham of the Cambridge Computer Laboratory, and the algorithm was presented in an unpublished technical report in 1997 (Needham and Wheeler, 1997). It is not subject to any patents. duplicate of for template reasons File links The following pages link to this file: XTEA Categories: Public domain images ... Roger Needham in 1999 Roger Michael Needham (February 9, 1935–February 28, 2003) was a British computer scientist. ... David John Wheeler (9 February 1927–13 December 2004) was a computer scientist. ... 1997 (MCMXCVII in Roman) is a common year starting on Wednesday of the Gregorian calendar. ... General Designer(s) Roger Needham and David Wheeler First published 1994 Derived from - Cipher(s) based on this design XTEA Algorithm detail Block size(s) 64 bits Key size(s) 128 bits Structure Feistel network Number of rounds variable; recommended 64 Feistel rounds; 32 cycles Best cryptanalysis TEA suffers from... In modern cryptography, symmetric key ciphers are generally divided into stream ciphers and block ciphers. ... In cryptography, the key size (alternatively key length) is a measure of the number of possible keys which can be used in a cipher. ... In cryptography, a Feistel cipher is a block cipher with a particular structure, named after IBM cryptographer Horst Feistel; it is also commonly known as a Feistel network. ... 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. ... 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. ... Differential cryptanalysis is a general form of cryptanalysis applicable primarily to block ciphers, but also to stream ciphers and cryptographic hash functions. ... A chosen plaintext attack is any form of cryptanalysis which presumes that the attacker has the capability to choose arbitrary plaintexts to be encrypted and obtain the corresponding ciphertexts. ... The German Lorenz cipher machine Cryptography or cryptology is a field of mathematics and computer science concerned with information security and related issues, particularly encryption. ... Encryption Decryption In cryptography, a block cipher is a symmetric key cipher which operates on fixed-length groups of bits, termed blocks, with an unvarying transformation. ... General Designer(s) Roger Needham and David Wheeler First published 1994 Derived from - Cipher(s) based on this design XTEA Algorithm detail Block size(s) 64 bits Key size(s) 128 bits Structure Feistel network Number of rounds variable; recommended 64 Feistel rounds; 32 cycles Best cryptanalysis TEA suffers from... This article is about algorithms for encryption and decryption. ... David John Wheeler (9 February 1927–13 December 2004) was a computer scientist. ... Roger Needham in 1999 Roger Michael Needham (February 9, 1935–February 28, 2003) was a British computer scientist. ... The William Gates Building, which currently houses the Computer Laboratory The Computer Laboratory (CL) at Cambridge is the University of Cambridges computer science department. ... 1997 (MCMXCVII in Roman) is a common year starting on Wednesday of the Gregorian calendar. ... A patent is a set of exclusive rights granted by a state to a person for a fixed period of time in exchange for the regulated, public disclosure of certain details of a device, method, process or composition of matter (substance) (known as an invention) which is new, inventive, and...


Like TEA, XTEA is a 64-bit block Feistel network with a 128-bit key and a suggested 64 rounds. Several differences from TEA are apparent, including a somewhat more complex key-schedule and a rearrangement of the shifts, XORs and additions. In modern cryptography, symmetric key ciphers are generally divided into stream ciphers and block ciphers. ... In cryptography, a Feistel cipher is a block cipher with a particular structure, named after IBM cryptographer Horst Feistel; it is also commonly known as a Feistel network. ... In cryptography, the key size (alternatively key length) is a measure of the number of possible keys which can be used in a cipher. ... Exclusive disjunction (usual symbol xor) is a logical operator that results in true if one of the operands (not both) is true. ...


Presented along with XTEA was a variable-width block cipher termed Block TEA, which uses the XTEA round function but applies it cyclically across an entire message for several iterations. Because it operates on the entire message, Block TEA has the property that it does not need a mode of operation. An attack on the full Block TEA was described in (Saarinen, 1998), which also details a weakness in Block TEA's successor, XXTEA. In cryptography, a block cipher operates on blocks of fixed length, often 64 or 128 bits. ...


As of 2004, the best attack reported on XTEA is a related-key differential attack on 26 out of 64 rounds of XTEA, requiring 220.5 chosen plaintexts and a time complexity of 2115.15 (Ko et al, 2004). 2004 is a leap year starting on Thursday of the Gregorian calendar. ... 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. ... Differential cryptanalysis is a general form of cryptanalysis applicable primarily to block ciphers, but also to stream ciphers and cryptographic hash functions. ... A chosen plaintext attack is any form of cryptanalysis which presumes that the attacker has the capability to choose arbitrary plaintexts to be encrypted and obtain the corresponding ciphertexts. ... Complexity theory is part of the theory of computation dealing with the resources required during computation to solve a given problem. ...


Implementations

This standard C source code, released into the public domain by David Wheeler and Roger Needham, encrypts and decrypts using XTEA: The C Programming Language, Brian Kernighan and Dennis Ritchie, the original edition that served for many years as an informal specification of the language The C programming language is a standardized imperative computer programming language developed in the early 1970s by Dennis Ritchie for use on the Unix operating system. ... The public domain comprises the body of all creative works and other knowledge—writing, artwork, music, science, inventions, and others—in which no person or organization has any proprietary interest. ...

 void encipher(unsigned long* v, unsigned long* k) { unsigned long v0=v[0], v1=v[1], i; unsigned long sum=0, delta=0x9E3779B9; for(i=0; i<32; i++) { v0 += ((v1 << 4 ^ v1 >> 5) + v1) ^ (sum + k[sum & 3]); sum += delta; v1 += ((v0 << 4 ^ v0 >> 5) + v0) ^ (sum + k[sum>>11 & 3]); } v[0]=v0; v[1]=v1; } void decipher(unsigned long* v, unsigned long* k) { unsigned long v0=v[0], v1=v[1], i; unsigned long sum=0xC6EF3720, delta=0x9E3779B9; for(i=0; i<32; i++) { v1 -= ((v0 << 4 ^ v0 >> 5) + v0) ^ (sum + k[sum>>11 & 3]); sum -= delta; v0 -= ((v1 << 4 ^ v1 >> 5) + v1) ^ (sum + k[sum & 3]); } v[0]=v0; v[1]=v1; } 

References

  • Youngdai Ko, Seokhie Hong, Wonil Lee, Sangjin Lee, and Jongin Lim. "Related key differential attacks on 26 rounds of XTEA and full rounds of GOST." In Proceedings of FSE '04, Lecture Notes in Computer Science, 2004. Springer-Verlag.
  • Seokhie Hong, Deukjo Hong, Youngdai Ko, Donghoon Chang, Wonil Lee, and Sangjin Lee. "Differential cryptanalysis of TEA and XTEA." In Proceedings of ICISC 2003, 2003b.
  • Dukjae Moon, Kyungdeok Hwang, Wonil Lee, Sangjin Lee, and Jongin Lim. "Impossible differential cryptanalysis of reduced round XTEA and TEA." Lecture Notes in Computer Science, 2365: 49-60, 2002. ISSN 0302-9743.
  • Roger M. Needham and David J. Wheeler. "Tea extensions." Technical report, Computer Laboratory, University of Cambridge, October 1997 (PDF).
  • Vikram Reddy Andem. A Cryptanalysis of the Tiny Encryption Algorithm, Masters thesis, The University of Alabama, Tuscaloosa, 2003.
  • Markku-Juhani Saarinen. "Cryptanalysis of Block TEA." Unpublished manuscript, October 1998. Can be found on the author's homepage or in the sci.crypt.research Usenet archive.

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. ... The Springer-Verlag (pronounced SHPRING er FAIR lahk) was a worldwide publishing company base in Germany. ... Usenet is a distributed Internet discussion system that evolved from a general purpose UUCP network of the same name. ...

External links


Wikisource – The Free Library – is a Wikimedia project to build a free, wiki library of primary source texts, along with translations of source-texts into any language and other supporting materials. ...

Block ciphers edit
Algorithms: 3-Way | AES | Akelarre | Anubis | Blowfish | Camellia | CAST-128 | CAST-256 | CMEA | CS-Cipher | DEAL | DES | DES-X | FEAL | FOX | FROG | G-DES | GOST | ICE | IDEA | Iraqi | KASUMI | KHAZAD | Khufu and Khafre | LOKI89/91 | LOKI97 | Lucifer | MacGuffin | Madryga | MAGENTA | MARS | MISTY1 | MMB | NewDES | Noekeon | RC2 | RC5 | RC6 | REDOC | Red Pike | S-1 | SAFER | SEED | Serpent | SHACAL | SHARK | Skipjack | Square | TEA | Triple DES | Twofish | XTEA
Design: Feistel network | Key schedule | Product cipher | S-box | SPN Attacks: Brute force | Linear / Differential cryptanalysis | Mod n | Related key | XSL Standardization: AES process | CRYPTREC | NESSIE Misc: Avalanche effect | Block size | IV | Key size | Modes of operation | Piling-up lemma | Weak key

 
 

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