Guess‐and‐determine attacks on PANAMA‐like stream ciphers

Abstract

Guess-and-determine attack is a cryptanalysis method that has been applied to various stream ciphers. In this study, the authors study the guess-and-determine attacks on two ISO standardised, Panama-like stream ciphers: MUGI and Enocoro. Utilising the word-oriented structure of the two ciphers, they are able to launch heuristic guess-and-determine attacks in a more efficient manner. Their first target MUGI is both an ISO standard and a Japanese-government-selected CRYPTREC standard. By splitting its basic 64-bit words into 16-bit quarter-words, they are able to conduct a guess-and-determine attack with complexity 2 388 , much lower than its 1216-bit internal state size. Enocoro is a lightweight stream cipher family. It has two versions named according to key-length as Enocoro-80 and Enocoro-128v2. They provide the specific guessing paths and they are able to launch guess-and-determine attacks on Enocoro-80 and Enocoro-128v2 with complexities 2 88 and 2 144 , respectively. In addition to specific attacking results, they also find some generic rules that may help to improve the efficiency of guess-and-determine attacks in the future.