What a lovely hat

SLIM and LBCIoT are lightweight block ciphers proposed for IoT applications. We present differential meet-in-the-middle attacks on these ciphers and discuss several implementation variants and possible improvements of these attacks. Experimental validation also shows some results that may be of independent interest in the cryptanalysis of other ciphers. Namely, the problems with low-probability differentials and the questionable accuracy of standard complexity estimates of using filters.

Modern secure communication systems, such as iMessage, WhatsApp, and Signal include intricate mechanisms that aim to achieve very strong security properties. These mechanisms typically involve continuously merging in new fresh secrets into the keying material, which is used to encrypt messages during communications. In the literature, these mechanisms have been proven to achieve forms of Post Compromise Security (PCS): the ability to provide communication security even if the full state of a...

The eIDAS 2.0 regulation aims to develop interoperable digital identities for European citizens, and it has recently become law. One of its requirements is that credentials be unlinkable. Anonymous credentials (AC) allow holders to prove statements about their identity in a way that does not require to reveal their identity and does not enable linking different usages of the same credential. As a result, they are likely to become the technology that provides digital identity for...

This article proposes an extension for privacy-preserving applications to introduce sanctions or prohibition lists. When initiating a particular action, the user can prove, in addition to the application logic, that they are not part of the sanctions lists (one or more) without compromising sensitive data. We will show how this solution can be integrated into applications, using the example of extending Freedom Tool (a voting solution based on biometric passports). We will also consider ways...

The circulant twin column parity mixer (TCPM) is a type of mixing layer for the round function of cryptographic permutations designed by Hirch et al. at CRYPTO 2023. It has a bitwise differential branch number of 12 and a bitwise linear branch number of 4, which makes it competitive in applications where differential security is required. Hirch et al. gave a concrete instantiation of a permutation using such a mixing layer, named Gaston, and showed the best 3-round differential and linear...

Modern micro-architectural attacks use a variety of building blocks chained to develop a final exploit. However, since in most cases, the footprint of such attacks is not visible architecturally (like, in the file-system), it becomes trickier to defend against these. In light of this, several automated defence mechanisms use Hardware Performance Counters (HPCs) detect when the micro-architectural elements are being misused for a potential attacks (like flush-reload, Spectre, Meltdown etc.)....

The analytical perspective employed in the study classifies the theoretical research on dependencies in differential characteristics into two types. By categorising all dependence representations from the value restrictions and the theory of quasidifferential trails, we pinpoint a specific set of nonlinear constraints, which we term linearised nonlinear constraints. We aim to establish a method that utilises value restrictions to identify these constraints, as the current method based on...

In the digital age, the concept of consent for online actions executed by third parties is crucial for maintaining trust and security in third-party services. This work introduces the notion of cryptographically secure digital consent, which aims to replicate the traditional consent process in the online world. We provide a flexible digital consent solution that accommodates different use cases and ensures the integrity of the consent process. The proposed framework involves a client...

APN functions offer optimal resistance to differential attacks and are instrumental in the design of block ciphers in cryptography. While finding APN functions is very difficult in general, a promising way to construct APN functions is through symmetric matrices called Quadratic APN matrices (QAM). It is known that the search space for the QAM method can be reduced by means of orbit partitions induced by linear equivalences. This paper builds upon and improves these approaches in the case of...

Scalability remains a key challenge for blockchain adoption. Rollups—especially zero-knowledge (ZK) and optimistic rollups—address this by processing transactions off-chain while maintaining Ethereum’s security, thus reducing gas fees and improving speeds. Cross-rollup bridges like Orbiter Finance enable seamless asset transfers across various Layer 2 (L2) rollups and between L2 and Layer 1 (L1) chains. However, the increasing reliance on these bridges raises significant security concerns,...

We present a novel approach for training neural networks that leverages packed Shamir secret sharing scheme. For specific training protocols based on Shamir scheme, we demonstrate how to realize the conversion between packed sharing and Shamir sharing without additional communication overhead. We begin by introducing a method to locally convert between Shamir sharings with secrets stored at different slots. Building upon this conversion, we achieve free conversion from packed sharing to...

Quantum information allows us to build quantum money schemes, where a bank can issue banknotes in the form of authenticatable quantum states that cannot be cloned or counterfeited: a user in possession of k banknotes cannot produce k +1 banknotes. Similar to paper banknotes, in existing quantum money schemes, a banknote consists of an unclonable quantum state and a classical serial number, signed by bank. Thus, they lack one of the most fundamental properties cryptographers look for in a...

Remote Keyless Entry (RKE) systems are ubiqui- tous in modern day automobiles, providing convenience for vehicle owners - occasionally at the cost of security. Most automobile companies have proprietary implementations of RKE; these are sometimes built on insecure algorithms and authentication mechanisms. This paper presents a compre- hensive study conducted on the RKE systems of multiple cars from four automobile manufacturers not previously explored. Specifically, we analyze the...

Pseudo-Random Injections (PRIs) have been used in several applications in symmetric-key cryptography, such as in the idealization of Authenticated Encryption with Associated Data (AEAD) schemes, building robust AEAD, and, recently, in converting a committing AEAD scheme into a succinctly committing AEAD scheme. In Crypto 2024, Bellare and Hoang showed that if an AEAD scheme is already committing, it can be transformed into a succinctly committing scheme by encrypting part of the plaintext...

In contemporary times, there are many situations where users need to verify that their information is correctly retained by servers. At the same time, servers need to maintain transparency logs. Many algorithms have been designed to address this problem. For example, Certificate Transparency (CT) helps track certificates issued by Certificate Authorities (CAs), while CONIKS aims to provide key transparency for end users. However, these algorithms often suffer from either high append time or...

We say there is a share conversion from a secret sharing scheme $\Pi$ to another scheme $\Pi'$ implementing the same access structure if each party can locally apply a deterministic function to their share to transform any valid secret sharing under $\Pi$ to a valid (but not necessarily random) secret sharing under $\Pi'$ of the same secret. If such a conversion exists, we say that $\Pi\ge\Pi'$. This notion was introduced by Cramer et al. (TCC'05), where they particularly proved that for...

Digital signature schemes based on multivariate- and code-based hard problems are promising alternatives for lattice-based signature schemes, due to their smaller signature size. Hence, several candidates in the ongoing additional standardization for quantum secure digital signature (DS) schemes by the National Institute of Standards and Technology (NIST) rely on such alternate hard problems. Gaussian Elimination (GE) is a critical component in the signing procedure of these schemes. In this...

Distributed mean estimation (DME) is a fundamental and important task as it serves as a subroutine in convex optimization, aggregate statistics, and, more generally, federated learning. The inputs for distributed mean estimation (DME) are provided by clients (such as mobile devices), and these inputs often contain sensitive information. Thus, protecting privacy and mitigating the influence of malicious adversaries are critical concerns in DME. A surge of recent works has focused on building...

In many multi-round public-coin interactive proof systems, challenges in different rounds serve different roles, but a formulation that actively utilizes this aspect has not been studied extensively. In this paper, we propose new notions called critical-round special honest verifier zero-knowledge and critical-round special soundness. Our notions are simple, intuitive, easy to apply, and capture several practical multi-round proof protocols including, but not limited to, those from the...

In a zero-knowledge proof market, we have two sides. On one side, bidders with proofs of different sizes and some private value to have this proof computed. On the other side, we have distributors (also called sellers) which have compute available to process the proofs by the bidders, and these distributors have a certain private cost to process these proofs (dependent on the size). More broadly, this setting applies to any online resource allocation where we have bidders who desire a...

The search for optimal differential trails for ARX ciphers is known to be difficult and scale poorly as the word size (and the branching through the carries of modular additions) increases.To overcome this problem, one may approximate the modular addition with the XOR operation, a process called linearization. The immediate drawback of this approach is that many valid and good trails are discarded. In this work, we explore different partial linearization trade-offs to model the modular...

Evaluation of cryptographic implementations with respect to side-channels has been mandated at high security levels nowadays. Typically, the evaluation involves four stages: detection, modeling, certification and secret recovery. In pursuit of specific goal at each stage, inherently different techniques used to be considered necessary. However, since the recent works of Eurocrypt2022 and Eurocrypt2024, linear regression analysis (LRA) has uniquely become the technique that is well-applied...

We provide explicit descriptions for radical 2-isogenies in dimensions one, two and three using theta coordinates. These formulas allow us to efficiently navigate in the corresponding isogeny graphs. As an application of this, we implement different versions of the CGL hash func- tion. Notably, the three-dimensional version is fastest, which demonstrates yet another potential of using higher dimensional isogeny graphs in cryptography.

Large polynomial multiplication is one of the computational bottlenecks in fully homomorphic encryption implementations. Usually, these multiplications are implemented using the number-theoretic transformation to speed up the computation. State-of-the-art GPU-based implementation of fully homomorphic encryption computes the number theoretic transformation in two different kernels, due to the necessary synchronization between GPU blocks to ensure correctness in computation. This can be a...

Liu et al. (ITCS22) initiated the study of designing a secure position verification protocol based on a specific proof of quantumness protocol and classical communication. In this paper, we study this interesting topic further and answer some of the open questions that are left in that paper. We provide a new generic compiler that can convert any single round proof of quantumness-based certified randomness protocol to a secure classical communication-based position verification scheme....

The Fiat-Shamir (FS) transform is the standard approach to compiling interactive proofs into non-interactive ones. However, the fact that knowledge extraction typically requires rewinding limits its applicability without having to rely on further heuristic conjectures. A better alternative is a transform that guarantees straight-line knowledge extraction. Two such transforms were given by Pass (CRYPTO '03) and Fischlin (CRYPTO '05), respectively, with the latter giving the most practical...

This paper addresses the problem of factoring composite numbers by introducing a novel approach to represent their prime divisors. We develop a method to efficiently identify smaller divisors based on the difference between the primes involved in forming the composite number. Building on these insights, we propose an algorithm that significantly reduces the computational complexity of factoring, requiring half as many iterations as traditional quadratic residue-based methods. The presented...

NTRU is one of the most extensively studied lattice-based schemes. Its flexible design has inspired different proposals constructed over different rings, with some aiming to enhance security and others focusing on improving performance. The literature has introduced a line of noncommutative NTRU-like designs that claim to offer greater resistance to existing attacks. However, most of these proposals are either theoretical or fall short in terms of time and memory requirements when compared...

There are two security notions for FHE schemes the traditional notion of IND-CPA, and a more stringent notion of IND-CPA$^D$. The notions are equivalent if the FHE schemes are perfectly correct, however for schemes with negligible failure probability the FHE parameters needed to obtain IND-CPA$^D$ security can be much larger than those needed to obtain IND-CPA security. This paper uses the notion of ciphertext drift in order to understand the practical difference between IND-CPA and...

Falcon is one of the three postquantum signature schemes already selected by NIST for standardization. It is the most compact among them, and offers excellent efficiency and security. However, it is based on a complex algorithm for lattice discrete Gaussian sampling which presents a number of implementation challenges. In particular, it relies on (possibly emulated) floating-point arithmetic, which is often regarded as a cause for concern, and has been leveraged in, e.g., side-channel...

Reductions are the workhorses of cryptography. They allow constructions of complex cryptographic primitives from simple building blocks. A prominent example is the non-interactive reduction from securely computing a ``complex" function $f$ to securely computing a ``simple" function $g$ via randomized encodings. Prior work equated simplicity with functions of small degree. In this work, we consider a different notion of simplicity where we require $g$ to only take inputs from a small...

One of the main candidates of post-quantum cryptography is lattice-based cryptography. Its cryptographic security against quantum attackers is based on the worst-case hardness of lattice problems like the shortest vector problem (SVP), which asks to find the shortest non-zero vector in an integer lattice. Asymptotic quantum speedups for solving SVP are known and rely on Grover's search. However, to assess the security of lattice-based cryptography against these Grover-like quantum speedups,...

A multi-signature scheme allows a list of signers to sign a common message. They are widely used in scenarios where the same message must be signed and transmitted by $N$ users, and, instead of concatenating $N$ individual signatures, employing a multi-signature can reduce the data to be sent. In recent years there have been numerous practical proposals in the discrete logarithm setting, such as MuSig2 (CRYPTO'21) for the Schnorr signature. Recently, these attempts have been extended to...

For a $q$-polynomial $L$ over a finite field $\mathbb{F}_{q^n}$, we characterize the differential spectrum of the function $f_L\colon \mathbb{F}_{q^n} \rightarrow \mathbb{F}_{q^n}, x \mapsto x \cdot L(x)$ and show that, for $n \leq 5$, it is completely determined by the image of the rational function $r_L \colon \mathbb{F}_{q^n}^* \rightarrow \mathbb{F}_{q^n}, x \mapsto L(x)/x$. This result follows from the classification of the pairs $(L,M)$ of $q$-polynomials in $\mathbb{F}_{q^n}[X]$, $n...

Information set decoding (ISD) algorithms currently offer the most powerful tool to solve the two archetypal problems of coding theory, namely the Codeword Finding Problem and the Syndrome Decoding Problem. Traditionally, ISD have primarily been studied for linear codes over finite fields, equipped with the Hamming metric. However, recently, other possibilities have also been explored. These algorithms have been adapted to different ambient spaces and metrics, such as the rank metric...

Recently, Baudrin et al. analyzed a special case of Wagner's commutative diagram cryptanalysis, referred to as commutative cryptanalysis. For a family $(E_k)_k$ of permutations on a finite vector space $G$, commutative cryptanalysis exploits the existence of affine permutations $A,B \colon G \rightarrow G$, $I \notin \{A,B\}$ such that $E_k \circ A (x) = B \circ E_k(x)$ holds with high probability, taken over inputs $x$, for a significantly large set of weak keys $k$. Several attacks...

We introduce superclass accountability, a new notion of accountability for security protocols. Classical notions of accountability typically aim to identify specific adversarial players whose violation of adversarial assumptions has caused a security failure. Superclass accountability describes a different goal: to prove the existence of adversaries capable of violating security assumptions. We develop a protocol design approach for realizing superclass accountability called the sting...

This document provides a specification guide for the Multi-party Computation (MPC) setup ceremony for the Tokamak zk-SNARK scheme. It begins by revisiting the MMORPG protocol proposed in BGM17 for Groth16 setup generation, which leverages a random beacon to ensure public randomness. Additionally, it explores the alternative design approach presented in the ``Snarky Ceremonies" paper KMSV21, which removes the need for a random beacon. The document includes a detailed pseudocode and workflow...

We consider the setting of asynchronous multi-party computation (AMPC) with optimal resilience $n=3t+1$ and linear communication complexity, and employ only ``lightweight'' cryptographic primitives, such as random oracle hash. In this model, we introduce two concretely efficient AMPC protocols for a circuit with $|C|$ multiplication gates: a protocol achieving fairness with $\mathcal{O}(|C|\cdot n + n^3)$ field elements of communication, and a protocol achieving guaranteed output delivery...

Federated Learning (FL) has gained lots of traction recently, both in industry and academia. In FL, a machine learning model is trained using data from various end-users arranged in committees across several rounds. Since such data can often be sensitive, a primary challenge in FL is providing privacy while still retaining utility of the model. Differential Privacy (DP) has become the main measure of privacy in the FL setting. DP comes in two flavors: central and local. In the former, a...

In the Dilithium digital signature scheme, there is an inherent tradeoff between the length of the public key, and the length of the signature. The coefficients of the main part of the public-key, the vector $\mathbf{t}$, are compressed (in a lossy manner), or "quantized", during the key-generation procedure, in order to save on the public-key size. That is, the coefficients are divided by some fixed denominator, and only the quotients are published. However, this results in some "skew"...

Recent advances in differentially private federated learning (DPFL) algorithms have found that using correlated noise across the rounds of federated learning (DP-FTRL) yields provably and empirically better accuracy than using independent noise (DP-SGD). While DP-SGD is well-suited to federated learning with a single untrusted central server using lightweight secure aggregation protocols, secure aggregation is not conducive to implementing modern DP-FTRL techniques without assuming a trusted...

This paper studies transaction execution mechanisms (TEMs) for blockchains, as the efficient resource allocation across multiple parallel executions queues or "local fee markets." We present a model considering capacity constraints, user valuations, and delay costs in a multi-queue system with an aggregate capacity constraint due to global consensus. We show that revenue maximization tends to allocate capacity to the highest-paying queue, while welfare maximization generally serves all...

Key agreement and public key encryption are two elementary cryptographic primitives, suitable for different scenarios. But their differences are still not familiar to some researchers. In this note, we show that the Safkhani et al.'s key agreement scheme [Peer-to-Peer Netw. Appl. 15(3), 1595-1616, 2022] is a public key encryption in disguise. We stress that the ultimate use of key agreement is to establish a shared key for some symmetric key encryption. We also present a simplification of...

For Password-Based Authenticated Key Exchange (PAKE), an idealized setup such as random oracle (RO) or a trusted setup such as common reference string (CRS) is a must in the universal composability (UC) framework (Canetti, FOCS 2001). Given the potential failure of a CRS or RO setup, it is natural to consider distributing trust among the two setups, resulting a CRS-or-RO-setup (i.e., CoR-setup). However, the infeasibility highlighted by Katz et al. (PODC 2014) suggested that it is...

The Cheon-Kim-Kim-Song (CKKS) scheme is renowned for its efficiency in encrypted computing over real numbers. However, it lacks an important functionality that most exact schemes have, an efficient modular reduction. This derives from the fundamental difference in encoding structure. The CKKS scheme encodes messages to the least significant bits, while the other schemes encode to the most significant bits (or in an equivalent manner). As a result, CKKS could enjoy an efficient rescaling but...

A hybrid cryptosystem combines two systems that fulfill the same cryptographic functionality, and its security enjoys the security of the harder one. There are many proposals for hybrid public-key encryption (hybrid PKE), hybrid signature (hybrid SIG) and hybrid authenticated key exchange (hybrid AKE). In this paper, we fill the blank of Hybrid Password Authentication Key Exchange (hybrid PAKE). For constructing hybrid PAKE, we first define an important class of PAKE -- full DH-type...

We improve recent generic proof systems for isogeny knowledge by Cong, Lai, Levin [26] based on circuit satisfiability, by using radical isogeny descriptions [19, 20] to prove a path in the underlying isogeny graph. We then present a new generic construction for a verifiable random function (VRF) based on a one-more type hardness assumption and zero-knowledge proofs. We argue that isogenies fit the constraints of our construction and instantiate the VRF with a CGL walk [22] and our new...

This paper describes a simple idea to improve (text) diffusion in block ciphers that use MDS codes but that take more than a single round to achieve full (text) diffusion. The Rijndael cipher family is used as an example since it comprises ciphers with different state sizes. A drawback of the new approach is the additional computational cost, but it is competitive compared to large MDS matrices used in the Khazad and Kuznyechik ciphers.

The Ducas-Micciancio (DM/FHEW) and Chilotti-Gama-Georgieva-Izabachène (CGGI/TFHE) cryptosystems provide a general privacy-preserving computation capability. These fully homomorphic encryption (FHE) cryptosystems can evaluate an arbitrary function expressed as a general look-up table (LUT) via the method of functional bootstrapping (also known as programmable bootstrapping). The main limitation of DM/CGGI functional bootstrapping is its efficiency because this procedure has to bootstrap every...

Folding schemes enable prover-efficient incrementally verifiable computation (IVC), where a proof is generated step-by-step, resulting in a space-efficient prover that naturally supports continuations. These attributes make them a promising choice for proving long-running machine executions (popularly, "zkVMs"). A major problem is designing an efficient read-write memory. Another challenge is overheads incurred by unused machine instructions when incrementally proving a program execution...

Recently, a more efficient attack on the initial tropical Stickel protocol has been proposed, different from the previously known Kotov-Ushakov attack, yet equally guaranteed to succeed. Given that the Stickel protocol can be implemented in various ways, such as utilizing platforms beyond the tropical semiring or employing alternative commutative matrix ``classes'' instead of polynomials, we firstly explore the generalizability of this new attack across different implementations of the...

We study differential additions formulas on Kummer lines that factorize through a degree $2$ isogeny $\phi$. We call the resulting formulas half differential additions: from the knowledge of $\phi(P), \phi(Q)$ and $P-Q$, the half differential addition allows to recover $P+Q$. We explain how Mumford's theta group theory allows, in any model of Kummer lines, to find a basis of the half differential relations. This involves studying the dimension $2$ isogeny $(P, Q) \mapsto (P+Q, P-Q)$. We...

Deep neural networks (DNNs) are valuable assets, yet their public accessibility raises security concerns about parameter extraction by malicious actors. Recent work by Carlini et al. (Crypto’20) and Canales- Martínez et al. (Eurocrypt’24) has drawn parallels between this issue and block cipher key extraction via chosen plaintext attacks. Leveraging differential cryptanalysis, they demonstrated that all the weights and biases of black-box ReLU-based DNNs could be inferred using a polynomial...

SQIsign is a well-known post-quantum signature scheme due to its small combined signature and public-key size. However, SQIsign suffers from notably long signing times, and verification times are not short either. To improve this, recent research has explored both one-dimensional and two-dimensional variants of SQIsign, each with distinct characteristics. In particular, SQIsign2D's efficient signing and verification times have made it a focal point of recent research. However, the absence of...

Tweakable enciphering modes (TEMs) provide security in a variety of storage and space-critical applications like disk and file-based encryption, and packet-based communication protocols, among others. XCB-AES (known as XCBv2) is specified in the IEEE 1619.2 standard for encryption of sector-oriented storage media and it comes with a proof of security for block-aligned input messages. In this work, we demonstrate the $\textit{first}$ and most efficient plaintext recovery attack on...

Non-interactive zero-knowledge (NIZK) proofs allow a prover to convince a verifier about the validity of an NP-statement by sending a single message and without disclosing any additional information (besides the validity of the statement). Single-message cryptographic proofs are very versatile, which has made them widely used both in theory and in practice. This is particularly true for succinct proofs, where the length of the message is sublinear in the size of the NP relation. This...

Masking is a sound countermeasure to protect against differential power analysis. Since the work by Balasch et al. in ASIACRYPT 2012, inner product masking has been explored as an alternative to the well known Boolean masking. In CARDIS 2017, Poussier et al. showed that inner product masking achieves higher-order security versus Boolean masking, for the same shared size, in the bit-probing model. Wang et al. in TCHES 2020 verified the inner product masking's security order amplification in...

Folding schemes are an exciting new primitive, transforming the task of performing multiple zero-knowledge proofs of knowledge for a relation into performing just one zero-knowledge proof, for the same relation, and a number of cheap inclusion-proofs. Recently, folding schemes have been used to amortize the cost associated with proving different statements to multiple distinct verifiers, which has various applications. We observe that for these uses, leaking information about the statements...

Time-lock puzzles are unique cryptographic primitives that use computational complexity to keep information secret for some period of time, after which security expires. This topic, while over 25 years old, is still in a state where foundations are not well understood: For example, current analysis techniques of time-lock primitives provide no sound mechanism to build composed multi-party cryptographic protocols which use expiring security as a building block. Further, there are analyses...

We show that the widely-used Schnorr signature scheme meets existential unforgeability under chosen-message attack (EUF-CMA) in the random oracle model (ROM) if the circular discrete-logarithm (CDL) assumption, a new, non-interactive and falsifiable variant of the discrete-log (DL) problem we introduce, holds in the underlying group. Notably, our reduction is tight, meaning the constructed adversary against CDL has essentially the same running time and success probability as the assumed...

Encrypted Search Algorithms (ESAs) are a technique to encrypt data while the user can still search over it. ESAs can protect privacy and ensure security of sensitive data stored on a remote storage. Originally, ESAs were used in the context of documents that consist of keywords. The user encrypts the documents, sends them to a remote server and is still able to search for keywords, without exposing information about the plaintext. The idea of ESAs has also been applied to relational...

In scenarios where a seller holds sensitive data $x$, like employee / patient records or ecological data, and a buyer seeks to obtain an evaluation of specific function $f$ on this data, solutions in trustless digital environments like blockchain-based Web3 systems typically fall into two categories: (1) Smart contract-powered solutions and (2) cryptographic solutions leveraging tools such as adaptor signatures. The former approach offers atomic transactions where the buyer learns the...

Keccak acts as the hash algorithm and eXtendable-Output Function (XOF) specified in the NIST standard drafts for Kyber and Dilithium. The Keccak output is highly correlated with sensitive information. While in RSA and ECDSA, hash-like components are only used to process public information, such as the message. The importance and sensitivity of hash-like components like Keccak are much higher in Kyber and Dilithium than in traditional public-key cryptography. However, few works study Keccak...

Datasets of side-channel leakage measurements are widely used in research to develop and benchmarking side-channel attack and evaluation methodologies. Compared to using custom and/or one-off datasets, widely-used and publicly available datasets improve research reproducibility and comparability. Further, performing high-quality measurements requires specific equipment and skills, while also taking a significant amount of time. Therefore, using publicly available datasets lowers the barriers...

In this paper, we investigate the rough order assumption (\(RO_C\)) introduced by Braun, Damgård, and Orlandi at CRYPTO 23, which posits that class groups of imaginary quadratic fields with no small prime factors in their order are computationally indistinguishable from general class groups. We present a novel attack that challenges the validity of this assumption by leveraging properties of Mordell curves over the rational numbers. Specifically, we demonstrate that if the rank of the...

SNOVA is one of the submissions in the NIST Round 1 Additional Signature of the Post-Quantum Signature Competition. SNOVA is a UOV variant that uses the noncommutative-ring technique to educe the size of the public key. SNOVA's public key size and signature size are well-balanced and have good performance. Recently, Beullens proposed a forgery attack against SNOVA, pointing out that the parameters of SNOVA can be attacked. Beullens also argued that with some slight adjustments his attacks...

In this paper, we explore a new type of key collisions called target-plaintext key collisions of AES, which emerge as an open problem in the key committing security and are directly converted into single-block collision attacks on Davies-Meyer (DM) hashing mode. For this key collision, a ciphertext collision is uniquely observed when a specific plaintext is encrypted under two distinct keys. We introduce an efficient automatic search tool designed to find target-plaintext key collisions....

We investigate the notion of bit-security for decisional cryptographic properties, as originally proposed in (Micciancio & Walter, Eurocrypt 2018), and its main variants and extensions, with the goal clarifying the relation between different definitions, and facilitating their use. Specific contributions of this paper include: (1) identifying the optimal adversaries achieving the highest possible MW advantage, showing that they are deterministic and have a very simple threshold...

Homomorphic message authenticators allow a user to perform computation on previously authenticated data producing a tag $\sigma$ that can be used to verify the authenticity of the computation. We extend this notion to consider a multi-party setting where we wish to produce a tag that allows verifying (possibly different) computations on all party's data at once. Moreover, the size of this tag should not grow as a function of the number of parties or the complexity of the computations. We...

Private set intersection (PSI) is a type of private set operation (PSO) for which concretely efficient linear-complexity protocols do exist. However, the situation is currently less satisfactory for other relevant PSO problems such as private set union (PSU): For PSU, the most promising protocols either rely entirely on computationally expensive public-key operations or suffer from substantial communication overhead. In this work, we present the first PSU protocol that is mainly based...

Peer-to-peer communication systems can provide many functions, including anonymized routing of network traffic, massive parallel computing environments, and distributed storage. Anonymity refers to the state of being completely nameless, with no attached identifiers. Pseudonymity involves the use of a fictitious name that can be consistently linked to a particular user, though not necessarily to the real identity. Both provide a layer of privacy, shielding the user's true identity from...

Attribute-based encryption (ABE) enables fine-grained control over which ciphertexts various users can decrypt. A master authority can create secret keys $sk_f$ with different functions (circuits) $f$ for different users. Anybody can encrypt a message under some attribute $x$ so that only recipients with a key $sk_f$ for a function such that $f(x)=1$ will be able to decrypt. There are a number of different approaches toward achieving selectively secure ABE, where the adversary has to decide...

Proofs of partial knowledge, first considered by Cramer, Damgård and Schoenmakers (CRYPTO'94) and De Santis et al. (FOCS'94), allow for proving the validity of $k$ out of $n$ different statements without revealing which ones those are. In this work, we present a new approach for transforming certain proofs system into new ones that allows for proving partial knowledge. The communication complexity of the resulting proof system only depends logarithmically on the total number of statements...

Signature-based witness encryption (SWE) is a recently proposed notion that allows to encrypt a message with respect to a tag $T$ and a set of signature verification keys. The resulting ciphertext can only be decrypted by a party who holds at least $k$ different valid signatures w.r.t. $T$ and $k$ different verification keys out of the $n$ keys specified at encryption time. Natural applications of this primitive involve distributed settings (e.g., blockchains), where multiple parties sign...

This paper initiates a concrete-security treatment of two-party secure computation. The first step is to propose, as target, a simple, indistinguishability-based definition that we call InI. This could be considered a poor choice if it were weaker than standard simulation-based definitions, but it is not; we show that for functionalities satisfying a condition called invertibility, that we define and show is met by functionalities of practical interest like PSI and its variants, the two...

Distributed training that enables multiple parties to jointly train a model on their respective datasets is a promising approach to address the challenges of large volumes of diverse data for training modern machine learning models. However, this approach immedi- ately raises security and privacy concerns; both about each party wishing to protect its data from other parties during training and preventing leakage of private information from the model after training through various...

Local Differential Privacy (LDP) provides a formal guarantee of privacy that enables the collection and analysis of sensitive data without revealing any individual's data. While LDP methods have been extensively studied, there is a lack of a systematic and empirical comparison of LDP methods for descriptive statistics. In this paper, we first provide a systematization of LDP methods for descriptive statistics, comparing their properties and requirements. We demonstrate that several mean...

Modern data analytics requires computing functions on streams of data points from many users that are challenging to calculate, due to both the high scale and nontrivial nature of the computation at hand. The need for data privacy complicates this matter further, as general-purpose privacy-enhancing technologies face limitations in at least scalability or utility. Existing work has attempted to improve this by designing purpose-built protocols for the use case of Private Stream Aggregation;...

True Random Number Generators (TRNGs) and Physically Unclonable Functions (PUFs) are critical hardware primitives for cryptographic systems, providing randomness and device-specific security. TRNGs require complete randomness, while PUFs rely on consistent, device-unique responses. In this work, both primitives are implemented on a System-on-Chip Field-Programmable Gate Array (SoC FPGA), leveraging the integrated Phase-Locked Loops (PLLs) for robust entropy generation in PLLbased TRNGs. A...

Ever since the seminal work of Diffie and Hellman, cryptographic (cyclic) groups have served as a fundamental building block for constructing cryptographic schemes and protocols. The security of these constructions can often be based on the hardness of (cyclic) group-based computational assumptions. Then, the generic group model (GGM) has been studied as an idealized model (Shoup, EuroCrypt 1997), which justifies the hardness of many (cyclic) group-based assumptions and shows the limits of...

Cryptography is a crucial method for ensuring the security of communication and data transfers across networks. While it excels on devices with abundant resources, such as PCs, servers, and smartphones, it may encounter challenges when applied to resource-constrained Internet of Things (IoT) devices like Radio Frequency Identification (RFID) tags and sensors. To address this issue, a demand arises for a lightweight variant of cryptography known as lightweight cryptography (LWC). In...

At Asiacrypt 2022, a holistic key guessing strategy was proposed to yield the most efficient key recovery for the rectangle attack. Recently, at Crypto 2023, a new cryptanalysis technique--the differential meet-in-the-middle (MITM) attack--was introduced. Inspired by these two previous works, we present three generic key recovery attacks in this paper. First, we extend the holistic key guessing strategy from the rectangle to the differential attack, proposing the generic classical...

Physically (or Physical) Unclonable Functions (PUFs) are basic and useful primitives in designing cryptographic systems. PUFs are designed to facilitate device authentication, secure boot, firmware integrity, and secure communications. To achieve these objectives, PUFs must exhibit both consistent repeatability and instance-specific randomness. The Arbiter PUF (APUF), recognized as the first silicon PUF, is capable of generating a substantial number of secret keys instantaneously based on...

Bit-decomposition-based zero-knowledge range proofs in the discrete logarithm (DLOG) setting with a transparent setup, e.g., Bulletproof (IEEE S\&P \textquotesingle 18), Flashproof (ASIACRYPT \textquotesingle 22), and SwiftRange (IEEE S\&P \textquotesingle 24), have garnered widespread popularity across various privacy-enhancing applications. These proofs aim to prove that a committed value falls within the non-negative range $[0, 2^N-1]$ without revealing it, where $N$ represents the bit...

Hardware Trojans (HTs) are a longstanding threat to secure computation. Among different threat models, it is the fabrication-time insertion of additional malicious logic directly into the layout of integrated circuits (ICs) that constitutes the most versatile, yet challenging scenario, for both attackers and defenders. Here, we present a large-scale, first-of-its-kind community effort through red-versus-blue teaming that thoroughly explores this threat. Four independently competing blue...

Recently, the construction of cryptographic schemes based on hard lattice problems has gained immense popularity. Apart from being quantum resistant, lattice-based cryptography allows a wide range of variations in the underlying hard problem. As cryptographic schemes can work in different environments under different operational constraints such as memory footprint, silicon area, efficiency, power requirement, etc., such variations in the underlying hard problem are very useful for designers...

We present novel Secure Multi-Party Computation (SMPC) protocols to perform Breadth-First-Searches (BFSs) and determine maximal flows on dense secret-shared graphs. In particular, we introduce a novel BFS protocol that requires only $\mathcal{O}(\log n)$ communication rounds on graphs with $n$ nodes, which is a big step from prior work that requires $\mathcal{O}(n \log n)$ rounds. This BFS protocol is then used in a maximal flow protocol based on the Edmonds-Karp algorithm, which requires...

Light clients implement a simple solution for Bitcoin's scalability problem, as they do not store the entire blockchain but only the state of particular addresses of interest. To be able to keep track of the updated state of their addresses, light clients rely on full nodes to provide them with the required information. To do so, they must reveal information about the addresses they are interested in. This paper studies the two most common light client implementations, SPV and Neutrino with...

Zero-Knowledge (ZK) protocols have been a subject of intensive study due to their fundamental importance and versatility in modern cryptography. However, the inherently different nature of quantum information significantly alters the landscape, necessitating a re-examination of ZK designs. A crucial aspect of ZK protocols is their round complexity, intricately linked to $\textit{simulation}$, which forms the foundation of their formal definition and security proofs. In the...

In this paper, we present the first third-party cryptanalysis of SCARF, a tweakable low-latency block cipher designed to thwart contention-based cache attacks through cache randomization. We focus on multiple-tweak differential attacks, exploiting biases across multiple tweaks. We establish a theoretical framework explaining biases for any number of rounds and verify this framework experimentally. Then, we use these properties to develop a key recovery attack on 7-round SCARF with a time...

Digital signatures ensure authenticity and secure communication. They are used to verify the integrity and authenticity of signed documents and are widely utilized in various fields such as information technologies, finance, education, and law. They are crucial in securing servers against cyber attacks and authenticating connections between clients and servers. Additionally, encryption is used in many areas, such as secure communication, cloud, server and database security to ensure data...

The see-in-the-middle (SITM) attack combines differential cryptanalysis and the ability to observe differential patterns in the side-channel leakage traces to reveal the secret key of SPN-based ciphers. While SITM presents a fresh perspective to side-channel analysis and allows attacks on deeper cipher rounds, there are practical difficulties that come with this method. First, one must realize a visual inspection of millions of power traces. Second, there is a strong requirement to reduce...

In recent years, cybersecurity has also become relevant for Operational Technology (OT). Critical systems like industrial automation systems or transportation systems are faced with new threats, and therefore require the implementation of thorough security measures. Regulations further mandate the deployment and regular verification of these security measures. However, OT systems differ from well-known systems of classic Information Technology (IT), such as mission times spanning decades,...

In this article, we derive the weight distribution of linear codes stemming from a subclass of (vectorial) $p$-ary plateaued functions (for a prime $p$), which includes all the explicitly known examples of weakly and non-weakly regular plateaued functions. This construction of linear codes is referred in the literature as the first generic construction. First, we partition the class of $p$-ary plateaued functions into three classes $\mathscr{C}_1, \mathscr{C}_2,$ and $\mathscr{C}_3$,...

Fully homomorphic encryption schemes are methods to perform compu- tations over encrypted data. Since its introduction by Gentry, there has been a plethora of research optimizing the originally inefficient cryptosystems. Over time, different families have emerged. On the one hand, schemes such as BGV, BFV, or CKKS excel at performing coefficient-wise addition or multiplication over vectors of encrypted data. In contrast, accumulator-based schemes such as FHEW and TFHE provide efficient...

In this article, we propose a generic hybrid encryption scheme providing entity authentication. The scheme is based on lossy trapdoor functions relying on the hardness of the Learning With Errors problem. The construction can be used on a number of different security requirements with minimal reconfiguration. It ensures entity authentication and ciphertext integrity while providing security against adaptive chosen ciphertext attacks in the standard model. As a desired characteristic of...

In recent years, ML based differential distinguishers have been explored and compared with the classical methods. Complexity of a key recovery attack on block ciphers is calculated using the probability of a differential distinguisher provided by classical methods. Since theoretical computations suffice to calculate the data complexity in these cases, so there seems no restrictions on the practical availability of computational resources to attack a block cipher using classical methods....

A Trusted Execution Environment (TEE) is a new type of security technology, implemented by CPU manufacturers, which guarantees integrity and confidentiality on a restricted execution environment to any remote verifier. TEEs are deployed on various consumer and commercial hardwareplatforms, and have been widely adopted as a component in the design of cryptographic protocols both theoretical and practical. Within the provable security community, the use of TEEs as a setup assumption has...

In this work, we consider the setting where one or more users with low computational resources would lie to outsource the task of proof generation for SNARKs to one external entity, named Prover. We study the scenario in which Provers have access to all statements and witnesses to be proven beforehand. We take a different approach to proof aggregation and design a new protocol that reduces simultaneously proving time and communication complexity, without going through recursive proof...