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IACR Transactions on Symmetric Cryptology
Number of Followers: 0  

  This is an Open Access Journal Open Access journal
ISSN (Online) 2519-173X
Published by Ruhr-Universit├Ąt Bochum Homepage  [4 journals]
  • Short Non-Malleable Codes from Related-Key Secure Block Ciphers, Revisited

    • Authors: Gianluca Brian, Antonio Faonio, João Ribeiro, Daniele Venturi
      Pages: 1 - 19
      Abstract: We construct non-malleable codes in the split-state model with codeword length m + 3λ or m + 5λ, where m is the message size and λ is the security parameter, depending on how conservative one is. Our scheme is very simple and involves a single call to a block cipher meeting a new security notion which we dub entropic fixed-related-key security, which essentially means that the block cipher behaves like a pseudorandom permutation when queried upon inputs sampled from a distribution with sufficient min-entropy, even under related-key attacks with respect to an arbitrary but fixed key relation. Importantly, indistinguishability only holds with respect to the original secret key (and not with respect to the tampered secret key).
      In a previous work, Fehr, Karpman, and Mennink (ToSC 2018) used a related assumption (where the block cipher inputs can be chosen by the adversary, and where indistinguishability holds even with respect to the tampered key) to construct a nonmalleable code in the split-state model with codeword length m + 2λ. Unfortunately, no block cipher (even an ideal one) satisfies their assumption when the tampering function is allowed to be cipher-dependent. In contrast, we are able to show that entropic fixed-related-key security holds in the ideal cipher model with respect to a large class of cipher-dependent tampering attacks (including those which break the assumption of Fehr, Karpman, and Mennink).
      PubDate: 2022-09-09
      DOI: 10.46586/tosc.v2022.i3.1-19
  • Invertible Quadratic Non-Linear Layers for MPC-/FHE-/ZK-Friendly Schemes
           over Fnp

    • Authors: Lorenzo Grassi, Silvia Onofri, Marco Pedicini, Luca Sozzi
      Pages: 20 - 72
      Abstract: Motivated by new applications such as secure Multi-Party Computation (MPC), Fully Homomorphic Encryption (FHE), and Zero-Knowledge proofs (ZK), many MPC-, FHE- and ZK-friendly symmetric-key primitives that minimize the number of multiplications over Fp for a large prime p have been recently proposed in the literature. This goal is often achieved by instantiating the non-linear layer via power maps x↦xd. In this paper, we start an analysis of new non-linear permutation functions over Fnp that can be used as building blocks in such symmetrickey primitives. Given a local map F : Fmp→ Fp, we limit ourselves to focus on S-Boxes over Fnp for n ≥ m defined as SF (x0, x1, . . . , xn−1) = y0 y1 . . . yn−1 where yi := F(xi, xi+1, . . . , xi+m−1). As main results, we prove that
      • given any quadratic function F : F2p→ Fp, the corresponding S-Box SF over Fnp for n ≥ 3 is never invertible;
      • similarly, given any quadratic function F : F3p → Fp, the corresponding S-Box SF over Fnp for n ≥ 5 is never invertible.
      Moreover, for each p ≥ 3, we present (1st) generalizations of the Lai-Massey construction over Fnp defined as before via functions F : Fmp → Fp for each n = m ≥ 2 and (2nd) (non-trivial) quadratic functions F : F3p → Fp such that SF over Fnp for n ∈ {3, 4} is invertible. As an open problem for future work, we conjecture that for each m ≥ 1 there exists a finite integer nmax(m) such that SF over Fnp defined as before via a quadratic function F : Fmp →Fp is not invertible for each n ≥ nmax(m). Finally, as a concrete application, we propose Neptune, a variant of the sponge hash function Poseidon, whose non-linear layer is designed by taking into account the results presented in this paper. We show that this variant leads to a concrete multiplication reduction with respect to Poseidon.
      PubDate: 2022-09-09
      DOI: 10.46586/tosc.v2022.i3.20-72
  • Algebraic Attacks against Some Arithmetization-Oriented Primitives

    • Authors: Augustin Bariant, Clémence Bouvier, Gaëtan Leurent, Léo Perrin
      Pages: 73 - 101
      Abstract: Recent advanced Zero-Knowledge protocols, along with other high-level constructions such as Multi-Party Computations (MPC), have highlighted the need for a new type of symmetric primitives that are not optimized for speed on the usual platforms (desktop computers, servers, microcontrollers, RFID tags...), but for their ability to be implemented using arithmetic circuits.
      Several primitives have already been proposed to satisfy this need. In order to enable an efficient arithmetization, they operate over large finite fields, and use round functions that can be modelled using low degree equations. The impact of these properties on their security remains to be completely assessed. In particular, algebraic attacks relying on polynomial root-finding become extremely relevant. Such attacks work by writing the cryptanalysis as systems of polynomial equations over the large field, and solving them with off-the-shelf tools (SageMath, NTL, Magma, . . . ).
      The need for further analysis of these new designs has been recently highlighted by the Ethereum Foundation, as it issued bounties for successful attacks against round-reduced versions of several of them.
      In this paper, we show that the security analysis performed by the designers (or challenge authors) of four such primitives is too optimistic, and that it is possible to improve algebraic attacks using insights gathered from a careful study of the round function.
      First, we show that univariate polynomial root-finding can be of great relevance n practice, as it allows us to solve many of the Ethereum Foundation’s challenges on Feistel–MiMC. Second, we introduce a trick to essentially shave off two full rounds at little to no cost for Substitution-Permutation Networks (SPN). This can be combined with univariate (resp. multivariate) root-finding, which allowed to solve some challenges for Poseidon (resp. Rescue–Prime). Finally, we also find an alternative way to set up a system of equations to attack Ciminion, leading to much faster attacks than expected by the designers.
      PubDate: 2022-09-09
      DOI: 10.46586/tosc.v2022.i3.73-101
  • New Low-Memory Algebraic Attacks on LowMC in the Picnic Setting

    • Authors: Fukang Liu, Willi Meier, Santanu Sarkar, Takanori Isobe
      Pages: 102 - 122
      Abstract: The security of the post-quantum signature scheme Picnic is highly related to the difficulty of recovering the secret key of LowMC from a single plaintext-ciphertext pair. Since Picnic is one of the alternate third-round candidates in NIST post-quantum cryptography standardization process, it has become urgent and important to evaluate the security of LowMC in the Picnic setting. The best attacks on LowMC with full S-box layers used in Picnic3 were achieved with Dinur’s algorithm. For LowMC with partial nonlinear layers, e.g. 10 S-boxes per round adopted in Picnic2, the best attacks on LowMC were published by Banik et al. with the meet-in-the-middle (MITM) method.
      In this paper, we improve the attacks on LowMC in a model where memory consumption is costly. First, a new attack on 3-round LowMC with full S-box layers with negligible memory complexity is found, which can outperform Bouillaguet et al.’s fast exhaustive search attack and can achieve better time-memory tradeoffs than Dinur’s algorithm. Second, we extend the 3-round attack to 4 rounds to significantly reduce the memory complexity of Dinur’s algorithm at the sacrifice of a small factor of time complexity. For LowMC instances with 1 S-box per round, our attacks are shown to be much faster than the MITM attacks. For LowMC instances with 10 S-boxes per round, we can reduce the memory complexity from 32GB (238 bits) to only 256KB (221 bits) using our new algebraic attacks rather than the MITM attacks, while the time complexity of our attacks is about 23.2 ∼ 25 times higher than that of the MITM attacks. A notable feature of our new attacks (apart from the 4-round attack) is their simplicity. Specifically, only some basic linear algebra is required to understand them and they can be easily implemented.
      PubDate: 2022-09-09
      DOI: 10.46586/tosc.v2022.i3.102-122
  • Cryptanalysis of Rocca and Feasibility of Its Security Claim

    • Authors: Akinori Hosoyamada, Akiko Inoue, Ryoma Ito, Tetsu Iwata, Kazuhiko Mimematsu, Ferdinand Sibleyras, Yosuke Todo
      Pages: 123 - 151
      Abstract: Rocca is an authenticated encryption with associated data scheme for beyond 5G/6G systems. It was proposed at FSE 2022/ToSC 2021(2), and the designers make a security claim of achieving 256-bit security against key-recovery and distinguishing attacks, and 128-bit security against forgery attacks (the security claim regarding distinguishing attacks was subsequently weakened in the full version in ePrint 2022/116). A notable aspect of the claim is the gap between the privacy and authenticity security. In particular, the security claim regarding key-recovery attacks allows an attacker to obtain multiple forgeries through the decryption oracle. In this paper, we first present a full key-recovery attack on Rocca. The data complexity of our attack is 2128 and the time complexity is about 2128, where the attack makes use of the encryption and decryption oracles, and the success probability is almost 1. The attack recovers the entire 256-bit key in a single-key and nonce-respecting setting, breaking the 256-bit security claim against key-recovery attacks. We then extend the attack to various security models and discuss several countermeasures to see the feasibility of the security claim. Finally, we consider a theoretical question of whether achieving the security claim of Rocca is possible in the provable security paradigm. We present both negative and positive results to the question.
      PubDate: 2022-09-09
      DOI: 10.46586/tosc.v2022.i3.123-151
  • New Cryptanalysis of ZUC-256 Initialization Using Modular Differences

    • Authors: Fukang Liu, Willi Meier, Santanu Sarkar, Gaoli Wang, Ryoma Ito, Takanori Isobe
      Pages: 152 - 190
      Abstract: ZUC-256 is a stream cipher designed for 5G applications by the ZUC team. Together with AES-256 and SNOW-V, it is currently being under evaluation for standardized algorithms in 5G mobile telecommunications by Security Algorithms Group of Experts (SAGE). A notable feature of the round update function of ZUC-256 is that many operations are defined over different fields, which significantly increases the difficulty to analyze the algorithm.
      As a main contribution, with the tools of the modular difference, signed difference and XOR difference, we develop new techniques to carefully control the interactions between these operations defined over different fields. At first glance, our techniques are somewhat similar to those developed by Wang et al. for the MD-SHA hash family. However, as ZUC-256 is quite different from the MD-SHA hash family and its round function is much more complex, we are indeed dealing with different problems and overcoming new obstacles.
      As main results, by utilizing complex input differences, we can present the first distinguishing attacks on 31 out of 33 rounds of ZUC-256 and 30 out of 33 rounds of the new version of ZUC-256 called ZUC-256-v2 with low time and data complexities, respectively. These attacks target the initialization phase and work in the related-key model with weak keys. Moreover, with a novel IV-correcting technique, we show how to efficiently recover at least 16 key bits for 15-round ZUC-256 and 14-round ZUC-256-v2 in the related-key setting, respectively. It is unpredictable whether our attacks can be further extended to more rounds with more advanced techniques. Based on the current attacks, we believe that the full 33 initialization rounds provide marginal security.
      PubDate: 2022-09-09
      DOI: 10.46586/tosc.v2022.i3.152-190
  • Attacks on the Firekite Cipher

    • Authors: Thomas Johansson, Willi Meier, Vu Nguyen
      Pages: 191 - 216
      Abstract: Firekite is a synchronous stream cipher using a pseudo-random number generator (PRNG) whose security is conjectured to rely on the hardness of the Learning Parity with Noise (LPN) problem. It is one of a few LPN-based symmetric encryption schemes, and it can be very efficiently implemented on a low-end SoC FPGA. The designers, Bogos, Korolija, Locher and Vaudenay, demonstrated appealing properties of Firekite, such as requiring only one source of cryptographically strong bits, small key size, high attainable throughput, and an estimate for the bit level security depending on the selected practical parameters.
      We propose distinguishing and key-recovery attacks on Firekite by exploiting the structural properties of its PRNG. We adopt several birthday-paradox techniques to show that a particular sum of Firekite’s output has a low Hamming weight with higher probability than the random case. We achieve the best distinguishing attacks with complexities 266.75 and 2106.75 for Firekite’s parameters corresponding to 80-bit and 128-bit security, respectively. By applying the distinguishing attacks and an additional algorithm we describe, one can also recover the secret matrix used in the Firekite PRNG, which is built from the secret key bits. This key recovery attack works on most large instances of Firekite parameters and has slightly larger complexity, for instance, 269.87 on the 80-bit security parameters n = 16,384, m = 216, k = 216.
      PubDate: 2022-09-09
      DOI: 10.46586/tosc.v2022.i3.191-216
  • Breaking HALFLOOP-24

    • Authors: Marcus Dansarie, Patrick Derbez, Gregor Leander, Lukas Stennes
      Pages: 217 - 238
      Abstract: HALFLOOP-24 is a tweakable block cipher that is used to protect automatic link establishment messages in high frequency radio, a technology commonly used by government agencies and industries that need highly robust long-distance communications. We present the first public cryptanalysis of HALFLOOP-24 and show that HALFLOOP-24, despite its key size of 128 bits, is far from providing 128 bit security. More precisely, we give attacks for ciphertext-only, known-plaintext, chosen-plaintext and chosen-ciphertext scenarios. In terms of their complexities, most of them can be considered practical. However, in the real world, the amount of available data is too low for our attacks to work. Our strongest attack, a boomerang key-recovery, finds the first round key with less than 210 encryption and decryption queries. In conclusion, we strongly advise against using HALFLOOP-24.
      PubDate: 2022-09-09
      DOI: 10.46586/tosc.v2022.i3.217-238
  • Finding Collisions against 4-Round SHA-3-384 in Practical Time

    • Authors: Senyang Huang, Orna Agmon Ben-Yehuda, Orr Dunkelman, Alexander Maximov
      Pages: 239 - 270
      Abstract: The Keccak sponge function family, designed by Bertoni et al. in 2007, was selected by the U.S. National Institute of Standards and Technology (NIST) in 2012 as the next generation of Secure Hash Algorithm (SHA-3). Due to its theoretical and practical importance, cryptanalysis of SHA-3 has attracted a lot of attention. Currently, the most powerful collision attack on SHA-3 is Jian Guo et al.’s linearisation technique. However, this technique is infeasible for variants with a
      smaller input space, such as SHA-3-384.
      In this work we improve upon previous results by utilising three ideas which were not used in previous works on collision attacks against SHA-3. First, we use 2-block messages instead of 1-block messages, to reduce constraints and increase flexibility in our solutions. Second, we reduce the connectivity problem into a satisfiability (SAT) problem, instead of applying the linearisation technique. Finally, we propose an efficient deduce-and-sieve algorithm on the basis of two new non-random properties
      of the Keccak non-linear layer.
      The resulting collision-finding algorithm on 4-round SHA-3-384 has a practical time complexity of 259.64 (and a memory complexity of 245.94). This greatly improves upon the best known collision attack so far: Dinur et al. achieved an impractical 2147 time complexity. Our attack does not threaten the security margin of the SHA-3 hash function. However, the tools developed in this paper could be used to analyse other cryptographic primitives as well as to develop new and faster SAT solvers.
      PubDate: 2022-09-09
      DOI: 10.46586/tosc.v2022.i3.239-270
  • Throwing Boomerangs into Feistel Structures

    • Authors: Hosein Hadipour, Marcel Nageler, Maria Eichlseder
      Pages: 271 - 302
      Abstract: Automatic tools to search for boomerang distinguishers have seen significant advances over the past few years. However, most previous work has focused on ciphers based on a Substitution Permutation Network (SPN), while analyzing the Feistel structure is of great significance. Boukerrou et al. recently provided a theoretical framework to formulate the boomerang switch over multiple Feistel rounds, but they did not provide an automatic tool to find distinguishers. In this paper, by enhancing the recently proposed method by Hadipour et al., we provide an automatic tool to search for boomerang distinguishers and apply it to block ciphers following the Generalized Feistel Structure (GFS). Applying our tool to a wide range of GFS ciphers, we show that it significantly improves the best previous results on boomerang analysis. In particular, we improve the best previous boomerang distinguishers for 20 and 21 rounds of WARP by a factor of 238.28 and 236.56, respectively. Thanks to he effectiveness of our method, we can extend the boomerang distinguishers of WARP by two rounds and distinguish 23 rounds of this cipher from a random permutation. Applying our method to the internationally-standardized cipher CLEFIA, we achieve a 9-round boomerang distinguisher which improves the best previous boomerang distinguisher by one round. Based on this distinguisher, we build a key-recovery attack on 11 rounds of CLEFIA, which improves the best previous sandwich attack on this cipher by one round. We also apply our method to LBlock, LBlock-s, and TWINE and improve the best previous boomerang distinguisher of these ciphers.
      PubDate: 2022-09-09
      DOI: 10.46586/tosc.v2022.i3.271-302
  • Towards Tight Differential Bounds of Ascon

    • Authors: Rusydi H. Makarim, Raghvendra Rohit
      Pages: 303 - 340
      Abstract: Being one of the winners of the CAESAR competition and a finalist of the ongoing NIST lightweight cryptography competition, the authenticated encryption with associated data algorithm Ascon has withstood extensive security evaluation. Despite the substantial cryptanalysis, the tightness on Ascon’s differential bounds is still not well-understood until very recently, at ToSC 2022, Erlacher et al. have proven lower bounds (not tight) on the number of differential and linear active Sboxes for 4 and 6 rounds. However, a tight bound for the minimum number of active Sboxes for 4 − 6 rounds is still not known.
      In this paper, we take a step towards solving the above tightness problem by efficiently utilizing both Satisfiability Modulo Theories (SMT) and Mixed Integer Linear Programming (MILP) based automated tools. Our first major contribution (using SMT) is the set of all valid configurations of active Sboxes (for e.g., 1, 3 and 11 active Sboxes at round 0, 1 and 2, respectively) up to 22 active Sboxes and partial sets for 23 to 32 active Sboxes for 3-round differential trails. We then prove that the weight (differential probability) of any 3-round differential trail is at least 40 by finding the minimum weights (using MILP) corresponding to each configuration till 19 active Sboxes. As a second contribution, for 4 rounds, we provide several necessary conditions (by extending 3 round trails) which may result in a differential trail with at most 44 active Sboxes. We find 5 new configurations for 44 active Sboxes and show that in total there are 9289 cases to check for feasibility in order to obtain the actual lower bound for 4 rounds. We also provide an estimate of the time complexity to solve these cases. Our third main contribution is the improvement in the 7-year old upper bound on active Sboxes for 4 and 5 rounds from 44 to 43 and from 78 to 72, respectively. Moreover, as a direct application of our approach, we find new 4-round linear trails with 43 active Sboxes and also a 5-round linear trail with squared correlation 2−184 while the previous best known linear trail has squared correlation 2−186. Finally, we provide the implementations of our SMT and MILP models, and actual trails to verify the correctness of results.
      PubDate: 2022-09-09
      DOI: 10.46586/tosc.v2022.i3.303-340
  • SuperBall: A New Approach for MILP Modelings of Boolean Functions

    • Authors: Ting Li, Yao Sun
      Pages: 341 - 367
      Abstract: Mixed Integer Linear Programming (MILP) solver has become one of the most powerful tools of searching for cryptographic characteristics. It has great significance to study the influencing factors of the efficiency of MILP models. For this goal, different types of MILP models should be constructed and carefully studied. As Boolean functions are the fundamental cryptographic components, in this paper, we study the descriptive models of Boolean functions. Here, a descriptive model of a Boolean function refers to a set of integer linear inequalities, where the set of the binary solutions to these inequalities is exactly the support of this Boolean function. Previously, it is hard to construct various types of descriptive models for study, one important reason is that only a few kinds of inequalities can be generated. On seeing this, a new approach, called SuperBall, is proposed to generate inequalities. The SuperBall approach is based on the method of undetermined coefficients, and it could generate almost all kinds of inequalities by appending appropriate constraints. Besides, the Sasaki-Todo Algorithm is also improved to construct the descriptive models from a set of candidate inequalities by considering both their sizes and strengths, while the strengths of descriptive models have not been considered in the previous works. As applications, we constructed several types of descriptive models for the Sboxes of Liliput, SKINNY-128, and AES. The experimental results first prove that the diversity of the inequalities generated by the SuperBall approach is good. More importantly, the results show that the strengths of descriptive model do affect the efficiencies, and although there is not a type of descriptive model having the best efficiency in all experiments, we did find a specific type of descriptive model which has the minimal size and relatively large strength, and the descriptive models of this type have better efficiencies in most of our experiments.
      PubDate: 2022-09-09
      DOI: 10.46586/tosc.v2022.i3.341-367
  • Hybrid Code Lifting on Space-Hard Block Ciphers

    • Authors: Yosuke Todo, Takanori Isobe
      Pages: 368 - 402
      Abstract: There is a high demand for whitebox cryptography from the practical use of encryption in untrusted environments. It has been actively discussed for two decades since Chow et al. presented the whitebox implementation of DES and AES. The goal is to resist the key extraction from the encryption program and mitigate the code lifting of the program. At CCS2015, Bogdanov and Isobe proposed space-hard block ciphers as a dedicated design of whitebox block ciphers. It ensures that the key extraction is as difficult as the key recovery in the standard blackbox model. Moreover, to mitigate code lifting, they introduce space hardness, a kind of leakage-resilient security with the incompressibility of a huge program. For space-hard ciphers, code lifting (a partial leakage of the entire program) is useless to copy the functionality.
      In this paper, we consider a new attack model of space-hard block ciphers called hybrid code lifting. Space-hard block ciphers are intended to ensure security under a size-bounded leakage. However, they do not consider attackers (in the standard blackbox model) receiving the leakage by code lifting. If such attackers can recover the encryption program of a space-hard block cipher, such a cipher does not always satisfy the intention. We analyze Yoroi proposed in TCHES 2021. We introduce the canonical representation of Yoroi. Using the representation enables the recovery of the programs of Yoroi-16 and Yoroi-32 with 233 and 265.6 complexities, respectively, in spite of slight leakage. The canonical representation causes another attack against Yoroi. It breaks an authors’ security claim about the “longevity”. We additionally analyzed SPNbox proposed in Asiacrypt 2016. As a result, considering security on the hybrid code lifting, the original number of rounds is insufficient to achieve 128-bit security under quarter-size leakage.
      PubDate: 2022-09-09
      DOI: 10.46586/tosc.v2022.i3.368-402
  • Low-Latency Boolean Functions and Bijective S-boxes

    • Authors: Shahram Rasoolzadeh
      Pages: 403 - 447
      Abstract: In this paper, we study the gate depth complexity of (vectorial) Boolean functions in the basis of {NAND, NOR, INV} as a new metric, called latency complexity, to mathematically measure the latency of Boolean functions. We present efficient algorithms to find all Boolean functions with low-latency complexity, or to determine the latency complexity of the (vectorial) Boolean functions, and to find all the circuits with the minimum latency complexity for a given Boolean function. Then, we present another algorithm to build bijective S-boxes with low-latency complexity which with respect to the computation cost, this algorithm overcomes the previous methods of building S-boxes.
      As a result, for latency complexity 3, we present n-bit S-boxes of 3 ≤ n ≤ 8 with linearity 2n−1 and uniformity 2n−2 (except for 5-bit S-boxes for whose the minimum achievable uniformity is 6). Besides, for latency complexity 4, we present several n-bit S-boxes of 5 ≤ n < 8 with linearity 2n−2 and uniformity 2n−4.
      PubDate: 2022-09-09
      DOI: 10.46586/tosc.v2022.i3.403-447
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