Paper 2005/383

Key Mixing in Block Ciphers through Addition modulo $2^n$

Debdeep Mukhopadhyay and Dipanwita RoyChowdhury

Abstract

The classical technique to perform key mixing in block ciphers is through exclusive-or (exor). In this paper we show that when the $n$-bit key is mixed in a block cipher of size $n$ bits via addition modulo $2^n$, the bias of the linear approximations falls exponentially fast. Experimental results have been provided to show that such a scheme cannot be cryptanalyzed using Linear Cryptanalysis.