Cryptanalysis of the stream cipher ABC v2

Abstract

ABC v2 is a software-efficient stream cipher with 128-bit key. In this paper, we apply a fast correlation attack to break ABC v2 with weak keys. There are about 296 weak keys in ABC v2. The complexity to identify a weak key and to recover the internal state of a weak key is low: identifying one weak key from about 232 random keys requires 6460 keystream bytes and 213.5 operations for each random key. Recovering the internal state of a weak key requires about 219.5 keystream bytes and 2 32.8 operations. A similar attack can be applied to break ABC v1 with much lower complexity than the previous attack on ABC v1. © Springer-Verlag Berlin Heidelberg 2007.