Invertible transformations over n-bit words are essen-tial ingredients in many cryptographic constructions. When n is
large (e.g., n = 64) such invertible transformations are usually rep-resented as a composition of simpler operations such as linear ...
Invertible transformations over n-bit words are essen-tial ingredients in many cryptographic constructions. When n is
large (e.g., n = 64) such invertible transformations are usually rep-resented as a composition of simpler operations such as linear func-tions, S-P networks, Feistel structures and T-functions. Among them we study T-functions which are probably invertible and are very useful in stream ciphers. In this paper we study some condi-
tions on a T-function h(x) such that f(x) = x + h(x) has a single cycle on Z2n.