Update on Enocoro stream cipher

Enocoro is a family of stream ciphers proposed by Watanabe et al. in 2007. It consists of two algorithms called Enocoro-80 and Enocoro-128v1.1, whose key lengths are 80 bits and 128 bits respectively. In this paper, we show that Enocoro-128v1.1 is vulnerable against the related-key attack in which we assume a stronger attacker than one in the related-key differential attack. The attack is applicable with 2¹¹² out of 2¹²⁸ keys and the calculation complexity of the attack is about 2⁶⁵. Our attack is mainly of theoretical interest and do not present a threat to practical applications using Enocoro-128v1.1. In addition, we propose to update Enocoro-128v1.1 to Enocoro-128v2 where a patch has been applied to prevent the attack.