Room 327

Normality of Boolean functions and its impact on stream cipher cryptanalysis

Sugata Gangopadhyay

IIT, Rourkee

A Boolean function is said to be k-normal (or, normal of order k) if it is
constant over a k dimensional flat. Boolean functions are used as a
combiner or filter functions in several stream ciphers. We will discuss the vulnerability of some stream ciphers due to high normality order of the filter
functions employed in their designs.