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).

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.