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 253.32 and requires 252 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.