Cryptanalysis of Lightweight WG-8 Stream Cipher

Abstract

WG-8 is a new lightweight variant of the well-known Welch-Gong (WG) stream cipher family, and takes an 80-bit secret key and an 80-bit initial vector (IV) as inputs. So far no attack on the WG-8 stream cipher has been published except the attacks by the designers. This paper shows that there exist Key-IV pairs for WG-8 that can generate keystreams, which are exact shifts of each other throughout the keystream generation. By exploiting this slide property, an effective key recovery attack on WG-8 in the related key setting is proposed, which has a time complexity of 2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">53.32</sup> and requires 2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">52</sup> chosen IVs. The attack is minimal in the sense that it only requires one related key. Furthermore, we present an efficient key recovery attack on WG-8 in the multiple related key setting. As confirmed by the experimental results, our attack recovers all 80 bits of WG-8 in on a PC with 2.5-GHz Intel Pentium 4 processor. This is the first time that a weakness is presented for WG-8, assuming that the attacker can obtain only a few dozen consecutive keystream bits for each IV. Finally, we give a new Key/IV loading proposal for WG-8, which takes an 80-bit secret key and a 64-bit IV as inputs. The new proposal keeps the basic structure of WG-8 and provides enough resistance against our related key attacks.