This paper shows practical committing attacks against Rocca-S, an authenticated encryption with associated data scheme designed for 6G applications. Previously, the best complexity of the attack was 2 64 by Derbez et al. in ToSC 2024(1)/FSE 2024. We show that the committing attack against Rocca by Takeuchi et al. in ToSC 2024(2)/FSE 2025 can be applied to Rocca-S, where Rocca is an earlier version of Rocca-S. We show a concrete test vector of our attack. We also point out a committing attack that exploits equivalent keys.

At CRYPTO 2017 and IEEE Transactions on Computers in 2018, Todo et al. proposed the division property based cube attack method making it possible to launch cube attacks with cubes of dimensions far beyond practical reach. However, assumptions are made to validate their attacks. In this paper, we further formulate the algebraic properties of the superpoly in one framework to facilitate cube attacks in more successful applications: we propose the “flag” technique to enhance the precision of MILP models, which enable us to identify proper non-cube IV assignments; a degree evaluation algorithm is presented to upper bound the degree of the superpoly s.t. the superpoly can be recovered without constructing its whole truth table and overall complexity of the attack can be largely reduced; we provide a divide-and-conquer strategy to Trivium-like stream ciphers namely Trivium, Kreyvium, TriviA-SC1/2 so that the large scale MILP models can be split into several small solvable ones enabling us to analyze Trivium-like primitives with more than 1000 initialization rounds; finally, we provide a term enumeration algorithm for finding the monomials of the superpoly, so that the complexity of many attacks can be further reduced. We apply our techniques to attack the initialization of several ciphers namely 839-round Trivium, 891-round Kreyvium, 1009-round TriviA-SC1, 1004-round TriviA-SC2, 184-round Grain-128a and 750-round Acorn respectively.

While impossible differential attack is one of the most well-known and familiar techniques for symmetric-key cryptanalysts, its subtlety and complicacy make the construction and verification of such attacks difficult and error-prone. We introduce a new set of notations for impossible differential analysis. These notations lead to unified formulas for estimation of data complexities of ordinary impossible differential attacks and attacks employing multiple impossible differentials. We also identify an interesting point from the new formulas: in most cases, the data complexity is only related to the form of the underlying distinguisher and has nothing to do with how the differences at the beginning and the end of the distinguisher propagate in the outer rounds. We check the formulas with some examples, and the results are all matching. Since the estimation of the time complexity is flawed in some situations, in this work, we show under which condition the formula is valid and give a simple time complexity estimation for impossible differential attack which is always achievable.

This paper provides security analysis of a lightweight block cipher called LILLIPUT, which was proposed in IEEE Transactions on Computers in 2015. LILLIPUT adopts an extended generalized Feistel network (EGFN). EGFN consists of non-linear, linear, and permutation layers, and the linear layer updates a part of the state only linearly, which causes several security concerns. Our first discovery is that the lower bounds of the number of differentially active S-boxes provided by the designers are incorrect. Thus the new bounds are derived by using mixed integer linear programming (MILP). We apply a two-stage search procedure introduced by Sun et al. that leads to tight bounds even for a large number of rounds. The search tool is then converted for linear cryptanalysis. With those updates, the challenging problem of evaluating LILLIPUT's security against differential and linear cryptanalysis is closed. Another contribution is the best third-party cryptanalysis. The designers expected EGFN to efficiently enhance security against integral cryptanalysis. However, security is not as enhanced as the designers expected. In fact, division property finds a 13-round distinguisher that improves on the previous distinguisher by 4 rounds. The distinguisher is further extended to a 17-round key recovery that improves on the previous best attack by 3 rounds.

The cube attack is a powerful cryptanalytic technique and is especially powerful against stream ciphers. Since we need to analyze the complicated structure of a stream cipher in the cube attack, the cube attack basically analyzes it by regarding it as a blackbox. Therefore, the cube attack is an experimental attack, and we cannot evaluate the security when the size of cube exceeds an experimental range, e.g., 40. In this paper, we propose cube attacks on non-blackbox polynomials. Our attacks are developed by using the division property, which is recently applied to various block ciphers. The clear advantage is that we can exploit large cube sizes because it never regards the cipher as a blackbox. We apply the new cube attack to Trivium, Grain128a, ACORN and Kreyvium. As a result, the secret keys of 832-round Trivium, 183-round Grain128a, 704-round ACORN and 872-round Kreyvium are recovered. These attacks are the current best key-recovery attack against these ciphers.