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Round function of
Designers Pascal Junod, Serge Vaudenay
First published 2003
Derived from IDEA
Cipher detail
Key sizes 0-256 bits
Block sizes 64 or 128 bits
Structure Lai-Massey scheme
Rounds 16
Best public cryptanalysis
Integral attack on 7 round NXT64 with time complexity of 2237.4 and on 5 round NXT128 with time complexity of 2205.6 by Wu Wenling, Zhang Wentao, and Feng Dengguo.[1]

In cryptography, the IDEA NXT algorithm (previously known as FOX) is a block cipher designed by Pascal Junod and Serge Vaudenay of EPFL (Lausanne, Switzerland). It was conceived between 2001 and 2003. The project was originally named FOX and was published in 2003. In May 2005 it was announced by MediaCrypt under the name IDEA NXT. IDEA NXT is the successor to the International Data Encryption Algorithm (IDEA) and also uses the Lai-Massey scheme.[2] MediaCrypt AG holds patents on elements of IDEA[citation needed] and IDEA NXT. The cipher is specified in two configurations: NXT64 (with block of 64 bits, key of 128 bits, 16 rounds) and NXT128 (with block of 128 bits, key of 256 bits, 16 rounds).


  1. ^ Wu Wenling; Zhang Wentao; Feng Dengguo (25 August 2005). "Improved Integral Cryptanalysis of FOX Block Cipher". 
  2. ^ "IDEA NXT Technical Description" (PDF). MediaCrypt. Archived from the original (PDF) on 28 September 2007. 

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