In the last years, a new line of research looking for alternative stream cipher constructions guaranteeing a higher TMD-TO resistance with smaller inner state lengths has emerged. So far, this has led to three generic constructions: the LIZARD construction, having a provable TMD-TO resistance of $2\cdot \mathit{SL}/3$; the Continuous-Key-Use construction, underlying the stream cipher proposals Sprout, Plantlet, and Fruit; and the Continuous-IV-Use construction, very recently proposed by Hamann, Krause, and Meier. Meanwhile, it could be shown that the Continuous-Key-Use construction is vulnerable against certain nontrivial distinguishing attacks.
In this paper, we present a formal framework for proving security lower bounds on the resistance of generic stream cipher constructions against TMD-TO attacks and analyze two of the constructions mentioned above. First, we derive a tight security lower bound of approximately $\min\{\mathit{KL},\mathit{SL}/2\}$ on the resistance of the Large-State-Small-Key construction. This shows that the feature $\mathit{KL}\le \mathit{SL}/2$ does not open the door for new nontrivial TMD-TO attacks against Trivium and Grain v1 which are more dangerous than the known ones. Second, we prove a maximal security bound on the TMD-TO resistance of the Continuous-IV-Use construction, which shows that designing concrete instantiations of ultra-lightweight Continuous-IV-Use stream ciphers is a hopeful direction of future research.
Category / Keywords: secret-key cryptography / Stream Ciphers, Generic Time-Memory-Data Tradeoff Attacks, Security Lower Bound Proofs, Random Oracle Models Date: received 2 Jan 2019 Contact author: hamann at uni-mannheim de Available format(s): PDF | BibTeX Citation Version: 20190109:004155 (All versions of this report) Short URL: ia.cr/2019/007