Lattice-based cryptography is in the process of being standardized. Several proposals to deal with side-channel information using lattice reduction exist. However, it has been shown that algorithms based on Bayesian updating are often more favorable in practice. In this work, we define distribution hints; a type of hint that allows modelling probabilistic information. These hints generalize most previously defined hints and the information obtained in several attacks. We define two...

As the use of the internet and digital devices has grown rapidly, keeping digital communications secure has become very important. Authenticated Key Agreement (AKA) protocols play a vital role in securing digital communications. These protocols enable the communicating parties to mutually authenticate and securely establish a shared secret key. The emergence of quantum computers makes many existing AKA protocols vulnerable to their immense computational power. Consequently, designing new...

Known attacks on the tropical implementation of Stickel protocol involve solving a minimal covering problem, and this leads to an exponential growth in the time required to recover the secret key as the used polynomial degree increases. Consequently, it can be argued that Alice and Bob can still securely execute the protocol by utilizing very high polynomial degrees, a feasible approach due to the efficiency of tropical operations. The same is true for the implementation of Stickel protocol...

Advanced Encryption Standard in Galois/Counter Mode (AES-GCM) is the most widely used Authenticated Encryption with Associated Data (AEAD) algorithm in the world. In this paper, we analyze the use of GCM with all the Initialization Vector (IV) constructions and lengths approved by NIST SP 800-38D when encrypting multiple plaintexts with the same key. We derive attack complexities in both ciphertext-only and known-plaintext models, with or without nonce hiding, for collision attacks...

Anticipating the advent of large quantum computers, NIST started a worldwide competition in 2016 aiming to define the next cryptographic standards. HQC is one of these post-quantum schemes still in contention, with four others already in the process of being standardized. In 2022, Guo et al. introduced a timing attack that exploited an inconsistency in HQC rejection sampling function to recover its secret key in 866,000 calls to an oracle. The authors of HQC updated its specification by...

Internet of Medical Things (IoMT) has gained significant research focus in both academic and medical institutions. Nevertheless, the sensitive data involved in IoMT raises concerns regarding user validation and data privacy. To address these concerns, certificateless signcryption (CLSC) has emerged as a promising solution, offering authenticity, confidentiality, and unforgeability. Unfortunately, most existing CLSC schemes are impractical for IoMT due to their heavy computational and storage...

In this paper, we study the robustness of Kyber, the Learning With Errors (LWE)-based Key Encapsulation Mechanism (KEM) chosen for standardization by NIST, against key mismatch attacks. We demonstrate that Kyber's security levels can be compromised with a few mismatch queries by striking a balance between the parallelization level and the cost of lattice reduction for post-processing. This highlights the imperative need to strictly prohibit key reuse in CPA-secure Kyber. We further...

Keeping decrypting parties accountable in public key encryption is notoriously hard since the secret key owner can decrypt any arbitrary ciphertext. Threshold encryption aims to solve this issue by distributing the power to decrypt among a set of parties, who must interact via a decryption protocol. However, such parties can employ cryptographic tools such as Multiparty Computation (MPC) to decrypt arbitrary ciphertexts without being detected. We introduce the notion of (threshold)...

This paper presents a generalization of the Learning With Rounding (LWR) problem, initially introduced by Banerjee, Peikert, and Rosen, by applying the perspective of vector quantization. In LWR, noise is induced by scalar quantization. By considering a new variant termed Learning With Quantization (LWQ), we explore large-dimensional fast-decodable lattices with superior quantization properties, aiming to enhance the compression performance over scalar quantization. We identify polar...

Unpredictable functions (UPFs) play essential roles in classical cryptography, including message authentication codes (MACs) and digital signatures. In this paper, we introduce a quantum analog of UPFs, which we call unpredictable state generators (UPSGs). UPSGs are implied by pseudorandom function-like states generators (PRFSs), which are a quantum analog of pseudorandom functions (PRFs), and therefore UPSGs could exist even if one-way functions do not exist, similar to other recently...

Byzantine consensus is a fundamental building block in distributed cryptographic problems. Despite decades of research, most existing asynchronous consensus protocols require a strong trusted setup and expensive public-key cryptography. In this paper, we study asynchronous Byzantine consensus protocols that do not rely on a trusted setup and do not use public-key cryptography such as digital signatures. We give an Asynchronous Common Subset (ACS) protocol whose security is only based on...

Fully Homomorphic Encryption (FHE) is a powerful Privacy-Enhancing Technology (PET) that enables computations on encrypted data without having access to the secret key. While FHE holds immense potential for enhancing data privacy and security, creating its practical applications is associated with many difficulties. A significant barrier is the absence of easy-to-use, standardized components that developers can utilize as foundational building blocks. Addressing this gap requires...

We propose a new key exchange protocol based on the Generalised Diffie-Hellman Key Exchange. In the latter, instead of using a group-action, we consider a semigroup action. In our proposal, the semigroup is the set of oriented knots in $\mathbb{S}^3$ with the operation of connected sum. As a semigroup action, we choose the action of the semigroup on itself through the connected sum. For the protocol to work, we need to use knot invariants, which allow us to create the shared secret key...

A function secret sharing (FSS) (Boyle et al., Eurocrypt 2015) is a cryptographic primitive that enables additive secret sharing of functions from a given function family $\mathcal{F}$. FSS supports a wide range of cryptographic applications, including private information retrieval (PIR), anonymous messaging systems, private set intersection and more. Formally, given positive integers $r \geq 2$ and $t < r$, and a class $\mathcal{F}$ of functions $f: [n] \to \mathbb{G}$ for an Abelian group...

$n$-out-of-$n$ distributed signatures are a special type of threshold $t$-out-of-$n$ signatures. They are created by a group of $n$ signers, each holding a share of the secret key, in a collaborative way. This kind of signatures has been studied intensively in recent years, motivated by different applications such as reducing the risk of compromising secret keys in cryptocurrencies. Towards maintaining security in the presence of quantum adversaries, Damgård et al. (J Cryptol 35(2), 2022)...

Soft Analytical Side Channel Attacks (SASCA) are a powerful family of Side Channel Attacks (SCA) that allows the recovery of secret values with only a small number of traces. Their effectiveness lies in the Belief Propagation (BP) algorithm, which enables efficient computation of the marginal distributions of intermediate values. Post-quantum schemes such as Kyber, and more recently, Hamming Quasi-Cyclic (HQC), have been targets of SASCA. Previous SASCA on HQC focused on Reed-Solomon (RS)...

At EUROCRYPT’23, Castryck and Decru, Maino et al., and Robert present efficient attacks against supersingular isogeny Diffie-Hellman key exchange protocol (SIDH). Drawing inspiration from these attacks, Andrea Basso, Luciano Maino, and Giacomo Pope introduce FESTA, an isogeny-based trapdoor function, along with a corresponding IND-CCA secure public key encryption (PKE) protocol at ASIACRYPT’23. FESTA incorporates either a diagonal or circulant matrix into the secret key to mask torsion...

Symmetric ratchets and one-way key chains play a vital role in numerous important security protocols such as TLS 1.3, DTLS 1.3, QUIC, Signal, MLS, EDHOC, OSCORE, and Apple PQ3. Despite the crucial role they play, very little is known about their security properties. This paper categorizes and examines different ratchet constructions, offering a comprehensive overview of their security. Our analysis reveals notable distinctions between different types of one-way key chains. Notably, the type...

Threshold symmetric encryption (TSE), introduced by Agrawal et al. [DiSE, CCS 2018], provides scalable and decentralized solution for symmetric encryption by ensuring that the secret-key stays distributed at all times. They avoid having a single point of attack or failure, while achieving the necessary security requirements. TSE was further improved by Christodorescu et al. [ATSE, CCS 2021] to support an amortization feature which enables a “more privileged” client to encrypt records in bulk...

The implementation security of post-quantum cryptography (PQC) algorithms has emerged as a critical concern with the PQC standardization process reaching its end. In a side-channel-assisted chosen-ciphertext attack, the attacker builds linear inequalities on secret key components and uses the belief propagation (BP) algorithm to solve. The number of inequalities leverages the query complexity of the attack, so the fewer the better. In this paper, we use the PQC standard algorithm Kyber512 as...

We analyse HWQCS, a code based signature scheme presented at ICISC 2023, which uses quasi-cyclic low density parity check codes (QC-LDPC). The scheme introduces high Hamming weight errors and signs each message using a fresh ephemeral secret key rather than using only one secret key, so to avoid known attacks on QC-LDPC signature schemes. In this paper, we show that the signatures of HWQCS leak substantial information concerning the ephemeral keys and formally describe this behaviour....

Number Theoretic Transform (NTT) has been widely used in accelerating computations in lattice-based cryptography. However, attackers can potentially launch power analysis targeting NTT because it is usually the most time-consuming part of the implementation. This extended time frame provides a natural window of opportunity for attackers. In this paper, we investigate the first CPU frequency leakage (Hertzbleed-like) attacks against NTT in lattice-based KEMs. Our key observation is that...

This paper questions the side-channel security of central reduction technique, which is widely adapted in efficient implementations of Lattice-Based Cryptography (LBC). We show that the central reduction leads to a vulnerability by creating a strong dependency between the power consumption and the sign of sensitive intermediate values. We exploit this dependency by introducing the novel absolute value prediction function, which can be employed in higher-order non-profiled multi-query...

In recent years, deep learning-based side-channel analysis (DLSCA) has become an active research topic within the side-channel analysis community. The well-known challenge of hyperparameter tuning in DLSCA encouraged the community to use methods that reduce the effort required to identify an optimal model. One of the successful methods is ensemble learning. While ensemble methods have demonstrated their effectiveness in DLSCA, particularly with AES-based datasets, their efficacy in analyzing...

Quantum no-cloning theorem gives rise to the intriguing possibility of quantum copy protection where we encode a program in a quantum state such that a user in possession of $k$ such states cannot create $k 1$ working copies. Introduced by Aaronson (CCC'09) over a decade ago, copy protection has proven to be notoriously hard to achieve. In this work, we construct public-key encryption and functional encryption schemes whose secret keys are copy-protected against unbounded collusions in...

Algorithm hardness can be described by 5 categories: hardness in computation, in sequential computation, in memory, in energy consumption (or bandwidth), in code size. Similarly, hardness can be a concern for solving or for verifying, depending on the context, and can depend on a secret trapdoor or be universally hard. Two main lines of research investigated such problems: cryptographic puzzles, that gained popularity thanks to blockchain consensus systems (where solving must be moderately...

We present a secret-key encryption scheme based on random rank metric ideal linear codes with a simple decryption circuit. It supports unlimited homomorphic additions and plaintext absorptions as well as a fixed arbitrary number of homomorphic multiplications. We study a candidate bootstrapping algorithm that requires no multiplication but additions and plaintext absorptions only. This latter operation is therefore very efficient in our scheme, whereas bootstrapping is usually the main...

This paper presents a comprehensive analysis of the verification algorithm of the CRYSTALS-Dilithium, focusing on a C reference implementation. Limited research has been conducted on its susceptibility to fault attacks, despite its critical role in ensuring the scheme’s security. To fill this gap, we investigate three distinct fault models - randomizing faults, zeroizing faults, and skipping faults - to identify vulnerabilities within the verification process. Based on our analysis, we...

CRYSTALS-Kyber is a key-encapsulation mechanism, whose security is based on the hardness of solving the learning-with-errors (LWE) problem over module lattices. As in its specification, Kyber prescribes the usage of the Number Theoretic Transform (NTT) for efficient polynomial multiplication. Side-channel assisted attacks against Post-Quantum Cryptography (PQC) algorithms like Kyber remain a concern in the ongoing standardization process of quantum-computer-resistant cryptosystems. Among the...

Physical attacks are serious threats to cryptosystems deployed in the real world. In this work, we propose a microarchitectural end-to-end attack methodology on generic lattice-based post-quantum key encapsulation mechanisms to recover the long-term secret key. Our attack targets a critical component of a Fujisaki-Okamoto transform that is used in the construction of almost all lattice-based key encapsulation mechanisms. We demonstrate our attack model on practical schemes such as Kyber and...

The LowMC family of SPN block cipher proposed by Albrecht et al. was designed specifically for MPC-/FHE-/ZKP-friendly use cases. It is especially used as the underlying block cipher of PICNIC, one of the alternate third-round candidate digital signature algorithms for NIST post-quantum cryptography standardization. The security of PICNIC is highly related to the difficulty of recovering the secret key of LowMC from a given plaintext/ciphertext pair, which raises new challenges for security...

The Peregrine signature scheme is one of the candidates in the ongoing Korean post-quantum cryptography competition. It is proposed as a high-speed variant of Falcon, which is a hash-and-sign signature scheme over NTRU lattices and one of the schemes selected by NIST for standardization. To this end, Peregrine replaces the lattice Gaussian sampler in the Falcon signing procedure with a new sampler based on the centered binomial distribution. While this modification offers significant...

In an effort to circumvent the high cost of standard countermeasures against side-channel attacks in post-quantum cryptography, some works have developed low-cost detection-based countermeasures. These countermeasures try to detect maliciously generated input ciphertexts and react to them by discarding the ciphertext or secret key. In this work, we take a look at two previously proposed low-cost countermeasures: the ciphertext sanity check and the decapsulation failure check, and demonstrate...

HQC is a code-based key encapsulation mechanism (KEM) that was selected to move to the fourth round of the NIST post-quantum standardization process. While this scheme was previously targeted by side-channel assisted chosen-ciphertext attacks for key recovery, all these attacks have relied on malformed ciphertexts for key recovery. Thus, all these attacks can be easily prevented by deploying a detection based countermeasures for invalid ciphertexts, and refreshing the secret key upon...

One-way functions are central to classical cryptography. They are both necessary for the existence of non-trivial classical cryptosystems, and sufficient to realize meaningful primitives including commitments, pseudorandom generators and digital signatures. At the same time, a mounting body of evidence suggests that assumptions even weaker than one-way functions may suffice for many cryptographic tasks of interest in a quantum world, including bit commitments and secure multi-party...

In post-quantum cryptography, Learning With Errors (LWE) is one of the dominant underlying mathematical problems. The dual attack is one of the main strategies for solving the LWE problem, and it has recently gathered significant attention within the research community. The attack strategy consists of a lattice reduction part and a distinguishing part. The latter includes an enumeration subroutine over a certain number of positions of the secret key. Our contribution consists of giving a...

We present a set of physical profiled attacks against CRYSTALS-Dilithium that accumulate noisy knowledge on secret keys over multiple signatures, finally leading to a full recovery attack. The methodology is composed of two steps. The first step consists of observing or inserting a bias in the posterior distribution of sensitive variables. The second step of an information processing phase which is based on belief propagation, which allows effectively exploiting that bias. The proposed...

The identity-based signature, initially introduced by Shamir [Sha84], plays a fundamental role in the domain of identity-based cryptography. It offers the capability to generate a signature on a message, allowing any user to verify the authenticity of the signature using the signer's identifier information (e.g., an email address), instead of relying on a public key stored in a digital certificate. Another significant concept in practical applications is the threshold signature, which serves...

Extremely Lossy Functions (ELFs) are families of functions that, depending on the choice during key generation, either operate in injective mode or instead have only a polynomial image size. The choice of the mode is indistinguishable to an outsider. ELFs were introduced by Zhandry (Crypto 2016) and have been shown to be very useful in replacing random oracles in a number of applications. One open question is to determine the minimal assumption needed to instantiate ELFs. While all...

Fine-grained cryptography is constructing cryptosystems in a setting where an adversary’s resource is a-prior bounded and an honest party has less resource than an adversary. Currently, only simple form of encryption schemes, such as secret-key and public-key encryption, are constructed in this setting. In this paper, we enrich the available tools in fine-grained cryptography by proposing the first fine-grained secure attribute-based encryption (ABE) scheme. Our construction is adaptively...

In this paper, we construct the first provably-secure isogeny-based (partially) blind signature scheme. While at a high level the scheme resembles the Schnorr blind signature, our work does not directly follow from that construction, since isogenies do not offer as rich an algebraic structure. Specifically, our protocol does not fit into the "linear identification protocol" abstraction introduced by Hauck, Kiltz, and Loss (EUROCYRPT'19), which was used to generically construct...

In this work, we construct the first digital signature (SIG) and public-key encryption (PKE) schemes with almost tight multi-user security under adaptive corruptions based on the learning-with-errors (LWE) assumption in the standard model. Our PKE scheme achieves almost tight IND-CCA security and our SIG scheme achieves almost tight strong EUF-CMA security, both in the multi-user setting with adaptive corruptions. The security loss is quadratic in the security parameter, and independent of...

In this paper, we study the decoding failure rate (DFR) of non-binary QC-MDPC codes using theoretical tools, extending the results of previous binary QC-MDPC code studies. The theoretical estimates of the DFR are particularly significant for cryptographic applications of QC-MDPC codes. Specifically, in the binary case, it is established that exploiting decoding failures makes it possible to recover the secret key of a QC-MDPC cryptosystem. This implies that to attain the desired security...

In this work, we propose a novel single-trace key recovery attack targeting side-channel leakage from the key-generation and encryption procedure of Kyber KEM. Our attack exploits the inherent nature of the Module-Learning With Errors (Module-LWE) problem used in Kyber KEM. We demonstrate that the inherent reliance of Kyber KEM on the Module-LWE problem results in higher number of repeated and secret key-related computations, referred to as STAMPs appearing on a single side channel trace,...

We present new protocols for threshold Schnorr signatures that work in an asynchronous communication setting, providing robustness and optimal resilience. These protocols provide unprecedented performance in terms of communication and computational complexity. In terms of communication complexity, for each signature, a single party must transmit a few dozen group elements and scalars across the network (independent of the size of the signing committee). In terms of computational...

Unbalanced Oil and Vinegar is a multivariate signature scheme that was introduced in 1999. Most multivariate candidates for signature schemes at NIST's PQC standardization process are either based on UOV or closely related to it. The UOV trapdoor is a secret subspace, the "oil subspace". We show how to recover an equivalent secret key from the knowledge of a single vector in the oil subspace in any characteristic. The reconciliation attack was sped-up by adding some bilinear equations...

Masking is a well-studied method for achieving provable security against side-channel attacks. In masking, each sensitive variable is split into $d$ randomized shares, and computations are performed with those shares. In addition to the computational overhead of masked arithmetic, masking also has a storage cost, increasing the requirements for working memory and secret key storage proportionally with $d$. In this work, we introduce mask compression. This conceptually simple technique is...

Isogeny-based cryptography is one of the candidates for post-quantum cryptography. In 2023, Kani's theorem breaks an isogeny-based scheme SIDH, which was considered a promising post-quantum scheme. Though Kani's theorem damaged isogeny-based cryptography, some researchers have been trying to dig into the applications of this theorem. A FESTA trapdoor function is an isogeny-based trapdoor function that is one trial to apply Kani's theorem to cryptography. This paper claims that there is an...

In response to side-channel attacks on masked implementations of post-quantum cryptographic algorithms, a new bitsliced higher-order masked implementation of CRYSTALS-Kyber has been presented at CHES'2022. The bitsliced implementations are typically more difficult to break by side-channel analysis because they execute a single instruction across multiple bits in parallel. However, in this paper, we reveal new vulnerabilities in the masked Boolean to arithmetic conversion procedure of this...

Perfect ciphers have been a very attractive cryptographic tool ever since C. Shannon described them. Note that, by definition, if a perfect cipher is used, no one can get any information about the encrypted message without knowing the secret key. We consider the problem of reducing the key length of perfect ciphers, because in many applications the length of the secret key is a crucial parameter. This paper describes a simple method of key length reduction. This method gives a perfect cipher...

We introduce a novel algebraic approach for attacking the McEliece cryptosystem which is currently at the $4$-th round of the NIST competition. The contributions of the article are twofold. (1) We present a new distinguisher on alternant and Goppa codes working in a much broader range of parameters than \cite{FGOPT11}. (2) With this approach we also provide a polynomial--time key recovery attack on alternant codes which are distinguishable with the distinguisher \cite{FGOPT11}. ...

The duplex construction is already well analyzed with many papers proving its security in the random permutation model. However, so far, the first phase of the duplex, where the state is initialized with a secret key and an initialization vector ($\mathit{IV}$), is typically analyzed in a worst case manner. More detailed, it is always assumed that the adversary is allowed to choose the $\mathit{IV}$ on its will. In this paper, we analyze how the security changes if restrictions on the choice...

Transport Layer Security (TLS) 1.3 and the Signal protocol are very important and widely used security protocols. We show that the key update function in TLS 1.3 and the symmetric key ratchet in Signal can be modeled as non-additive synchronous stream ciphers. This means that the efficient Time Memory Tradeoff Attacks for stream ciphers can be applied. The implication is that TLS 1.3, QUIC, DTLS 1.3, and Signal offer a lower security level against TMTO attacks than expected from the key...

Key mismatch attacks resilience is a great concern for KEMs in the NIST PQC standardization process. In key mismatch attacks, the adversary aims to recover the reused key by sending special form of ciphertexts to the target party and observing whether the shared key matches his guesses or not. In this paper, we propose pairwise-parallel key mismatch attacks on Kyber and other lattice-based KEMs. The strategy is to recover partial information about multiple secret key coefficient-pairs in...

The major objective of this paper is to present a theoretical model for an algorithm that has not been previously described in the literature, capable of generating a secret key through the transmission of data over a public channel. We explain how the method creates a shared secret key by attaining commutativity through the multiplication of the modular exponentiation of a minimum of two bases and an equal number of private exponents for each party involved in the exchange. In addition, we...

Identity-Based Encryption (IBE) was introduced in order to reduce the cost associated with Public Key Infrastructure systems. IBE allows users to request a trusted Key Generation Centre (KGC) for a secret key on a given identity, without the need to manage public keys. However, one of the main concerns of IBE is that the KGC has the power to decrypt all ciphertexts as it has access to all (identity, secret key) pairs. To address this issue, Chow (PKC 2009) introduced a new security property...

For decades now, mathematical complexity is being regarded as the sole means to creating a sufficient distance between a ciphertext and its generating plaintext. Alas, mathematical complexity operates under the irremovable shadow of stealth cryptanalysis. By its nature mathematical complexity is vulnerable to smarter mathematicians and better equipped adversaries, which is a sufficient motivation to explore an alternative means to project security. Applying the Innovation Solution Protocol...

Recent advances in the capabilities of large language models such as GPT-4 have spurred increasing concern about our ability to detect AI-generated text. Prior works have suggested methods of embedding watermarks in model outputs, by $\textit{noticeably}$ altering the output distribution. We ask: Is it possible to introduce a watermark without incurring $\textit{any detectable}$ change to the output distribution? To this end we introduce a cryptographically-inspired notion of undetectable...

A Distributed Key Generation (DKG) protocol is an essential component of threshold cryptography. DKGs enable a group of parties to generate a secret and public key pair in a distributed manner so that the secret key is protected from being exposed, even if a certain number of parties are compromised. Robustness further guarantees that the construction of the key pair is always successful, even if malicious parties try to sabotage the computation. In this paper, we construct two efficient...

Functional encryption (FE) is a primitive where the holder of a master secret key can control which functions a user can evaluate on encrypted data. It is a powerful primitive that even implies indistinguishability obfuscation (iO), given sufficiently compact ciphertexts (Ananth-Jain, CRYPTO'15 and Bitansky-Vaikuntanathan, FOCS'15). However, despite being extensively studied, there are FE schemes, such as function-hiding inner-product FE (Bishop-Jain-Kowalczyk, AC'15,...

Code-based cryptography has received a lot of attention recently because it is considered secure under quantum computing. Among them, the QC-MDPC based scheme is one of the most promising due to its excellent performance. QC-MDPC based scheme is usually subject to a small rate of decryption failure, which can leak information about the secret key. This raises two crucial problems: how to accurately estimate the decryption failure rate and how to use the failure information to recover the...

We propose a new cryptographic primitive called "verifiably encrypted threshold key derivation" (vetKD) that extends identity-based encryption with a decentralized way of deriving decryption keys. We show how vetKD can be leveraged on modern blockchains to build scalable decentralized applications (or "dapps") for a variety of purposes, including preventing front-running attacks on decentralized finance (DeFi) platforms, end-to-end encryption for decentralized messaging and social networks...

MQ-Sign is a variant of the UOV singature scheme proposed by Shim et al. It has been suggested as a candidate for the standardization of post-quantum cryptography in Republic of Korea (known as KpqC). However, recently Aulbach et al. proposed a practical key recovery attack against MQ-Sign-RS and MQ-Sign-SS with a simple secret key $\mathcal{S}$. In this paper, we propose another attack that is valid for the case of a general secret key $\mathcal{S}$.

We introduce a novel template attack for secret key recovery in Kyber, leveraging side-channel information from polynomial multiplication during decapsulation. Conceptually, our attack exploits that Kyber's incomplete number-theoretic transform (NTT) causes each secret coefficient to be used multiple times, unlike when performing a complete NTT. Our attack is a single trace \emph{known} ciphertext attack that avoids machine-learning techniques and instead relies on correlation-matching...

Two fundamental properties of quantum states that quantum information theory explores are pseudorandomness and provability of destruction. We introduce the notion of quantum pseudorandom states with proofs of destruction (PRSPD) that combines both these properties. Like standard pseudorandom states (PRS), these are efficiently generated quantum states that are indistinguishable from random, but they can also be measured to create a classical string. This string is verifiable (given the...

The secret key of any encryption scheme that are stored in secure memory of the hardwired devices can be tampered using fault attacks. The usefulness of tampering attack is to recover the key by altering some regions of the memory. Such attack may also appear when the device is stolen or viruses has been introduced. Non-malleable codes are used to protect the secret information from tampering attacks. The secret key can be encoded using non-malleable codes rather than storing it in plain...

Quantum key distribution (QKD) allows Alice and Bob to agree on a shared secret key, while communicating over a public (untrusted) quantum channel. Compared to classical key exchange, it has two main advantages: (i) The key is unconditionally hidden to the eyes of any attacker, and (ii) its security assumes only the existence of authenticated classical channels which, in practice, can be realized using Minicrypt assumptions, such as the existence of digital signatures. On the flip side, QKD...

In this paper we describe attacks on the UOV-based signature scheme called MQ-Sign. MQ-Sign was submitted by Shim, Kim, and An as a a first-round candidate for standardization in the (South) Korean post-quantum cryptography competition (KpqC). The scheme makes use of sparseness of the secret central polynomials and equivalent key construction to reduce the size of the private key. The authors propose four variants exploiting different levels of sparsity, MQ-Sign-SS, MQ-Sign-RS, MQ-Sign-SR,...

The Bitcoin architecture heavily relies on the ECDSA signature scheme which is broken by quantum adversaries as the secret key can be computed from the public key in quantum polynomial time. To mitigate this attack, bitcoins can be paid to the hash of a public key (P2PKH). However, the first payment reveals the public key so all bitcoins attached to it must be spent at the same time (i.e. the remaining amount must be transferred to a new wallet). Some problems remain with this approach: the...

Current solutions to quantum vulnerabilities of widely used cryptographic schemes involve migrating users to post-quantum schemes before quantum attacks become feasible. This work deals with protecting quantum procrastinators: users that failed to migrate to post-quantum cryptography in time. To address this problem in the context of digital signatures, we introduce a technique called signature lifting, that allows us to lift a deployed pre-quantum signature scheme satisfying a certain...

Due to recent cryptanalytical breakthroughs, the multivariate signature schemes that seemed to be most promising in the past years are no longer in the focus of the research community. Hence, the cryptographically mature UOV scheme is of great interest again. Since it has not been part of the NIST process for standardizing post-quantum cryptography so far, it has not been studied intensively for its physical security. In this work, we present a side-channel attack on the latest...

Quantum cryptography leverages many unique features of quantum information in order to construct cryptographic primitives that are oftentimes impossible classically. In this work, we build on the no-cloning principle of quantum mechanics and design cryptographic schemes with key-revocation capabilities. We consider schemes where secret keys are represented as quantum states with the guarantee that, once the secret key is successfully revoked from a user, they no longer have the ability to...

Among the fourth round finalists of the NIST post-quantum cryptography standardization process for public-key encryption algorithms and key encapsulation mechanisms, three rely on hard problems from coding theory. Key encapsulation mechanisms are frequently used in hybrid cryptographic systems: a public-key algorithm for key exchange and a secret key algorithm for communication. A major point is thus the initial key exchange that is performed thanks to a key encapsulation mechanism. In this...

Whereas theoretical attacks on standardized crypto primitives rarely lead to actual practical attacks, the situation is different for side-channel attacks. Improvements in the performance of side-channel attacks are of utmost importance. In this paper, we propose a framework to be used in key-recovery side-channel attacks on CCA-secure post-quantum encryption schemes. The basic idea is to construct chosen ciphertext queries to a plaintext checking oracle that collects information on a...

The no-cloning principle of quantum mechanics enables us to achieve amazing unclonable cryptographic primitives, which is impossible in classical cryptography. However, the security definitions for unclonable cryptography are tricky. Achieving desirable security notions for unclonability is a challenging task. In particular, there is no indistinguishable-secure unclonable encryption and quantum copy-protection for single-bit output point functions in the standard model. To tackle this...

In post-quantum cryptography (PQC), Learning With Errors (LWE) is one of the dominant underlying mathematical problems. For example, in NIST's PQC standardization process, the Key Encapsulation Mechanism (KEM) protocol chosen for standardization was Kyber, an LWE-based scheme. Recently the dual attack surpassed the primal attack in terms of concrete complexity for solving the underlying LWE problem for multiple cryptographic schemes, including Kyber. The dual attack consists of a reduction...

We give a construction of a 2-round blind signature scheme based on the hardness of standard lattice problems (Ring/Module-SIS/LWE and NTRU) with a signature size of 22 KB. The protocol is round-optimal and has a transcript size that can be as small as 60 KB. This blind signature is around $4$ times shorter than the most compact lattice-based scheme based on standard assumptions of del Pino and Katsumata (Crypto 2022) and around $2$ times shorter than the scheme of Agrawal et al. (CCS 2022)...

This paper presents a new profiling side-channel attack on CRYSTALS-Dilithium, the new NIST primary standard for quantum-safe digital signatures. An open source implementation of CRYSTALS-Dilithium is already available, with constant-time property as a consideration for side-channel resilience. However, this implementation does not protect against attacks that exploit intermediate data leakage. We show how to exploit a new leakage on a vector generated during the signing process, for which...

Shuffling is a well-known countermeasure against side-channel analysis. It typically uses the Fisher-Yates (FY) algorithm to generate a random permutation which is then utilized as the loop iterator to index the processing of the variables inside the loop. The processing order is scrambled as a result, making side-channel analysis more difficult. Recently, a side-channel attack on a masked and shuffled implementation of Saber requiring 61,680 power traces to extract the secret key was...

Post-quantum Cryptography (PQC) has reached the verge of standardization competition, with Kyber as a winning candidate. In this work, we demonstrate practical backdoor insertion in Kyber through kleptrography. The backdoor can be inserted using classical techniques like ECDH or post-quantum Classic Mceliece. The inserted backdoor targets the key generation procedure where generated output public keys subliminally leak information about the secret key to the owner of the backdoor. We...

Authenticated encryption with associated data (AEAD) forms the core of much of symmetric cryptography, yet the standard techniques for modeling AEAD assume recipients have no ambiguity about what secret key to use for decryption. This is divorced from what occurs in practice, such as in key management services, where a message recipient can store numerous keys and must identify the correct key before decrypting. To date there has been no formal investigation of their security properties or...

Recently, F.Ivanov, E.Krouk and V.Zyablov proposed new cryptosystem based of Generalized Reed--Solomon (GRS) codes over field extensions. In their approach, the subfield images of GRS codes are masked by a special transform, so that the resulting public codes are not equivalent to subfield images of GRS code but burst errors still can be decoded. In this paper, we show that the complexity of message-recovery attack on this cryptosystem can be reduced due to using burst errors, and the secret...

In 2009, Lyubashevsky proposed a lattice-based signature scheme by applying the Fiat-Shamir transformation and proved its security under the generalized compact knapsack (GCK) problem. This scheme has a simple structure but has large signature and key sizes due to the security requirement of their security reduction. Dilithium, which was submitted to the NIST Post-Quantum Cryptography standardization and selected as one of the final candidates, is an improvement of the Lyubashevsky's...

The quantum resistance Key Encapsulation Mechanism (PQC-KEM) design aims to replace cryptography in legacy security protocols. It would be nice if PQC-KEM were faster and lighter than ECDH or DH for easy migration to legacy security protocols. However, it seems impossible due to the temperament of the secure underlying problems in a quantum environment. Therefore, it makes reason to determine the threshold of the scheme by analyzing the maximum bandwidth the legacy security protocol can...

The hash function Romulus-H is a finalist in the NIST Lightweight Cryptography competition. It is based on the Hirose double block-length (DBL) construction which is provably secure when used with an ideal block cipher. However, in practice, ideal block ciphers can only be approximated. Therefore, the security of concrete instantiations must be cryptanalyzed carefully; the security margin may be higher or lower than in the secret-key setting. So far, the Hirose DBL construction has been...

The $\mathcal{S}_{leeve}$ construction proposed by Chaum et al. (ACNS'21) introduces an extra security layer for digital wallets by allowing users to generate a "back up key" securely nested inside the secret key of a signature scheme, i.e., ECDSA. The "back up key", which is secret, can be used to issue a "proof of ownership", i.e., only the real owner of this secret key can generate a single proof, which is based on the WOTS signature scheme. The authors of $\mathcal{S}_{leeve}$ proposed...

We present a key-recovery fault injection attack on the Classic McEliece Key Encapsulation Mechanism (KEM). The fault injections target the error-locator polynomial of the Goppa code and the validity checks in the decryption algorithm, making a chosen ciphertext attack possible. Faulty decryption outputs are used to generate a system of polynomial equations in the secret support elements of the Goppa code. After solving the equations, we can determine a suitable Goppa polynomial and form an...

Attribute-based encryption (ABE) generalizes public-key encryption and enables fine-grained control to encrypted data. However, ABE upends the traditional trust model of public-key encryption by requiring a single trusted authority to issue decryption keys. If an adversary compromises the central authority and exfiltrates its secret key, then the adversary can decrypt every ciphertext in the system. This work introduces registered ABE, a primitive that allows users to generate secret keys...

Ascon family is one of the finalists of the National Institute of Standards and Technology (NIST) lightweight cryptography standardization process. The family includes three Authenticated Encryption with Associated Data (AEAD) schemes: Ascon-128 (primary), Ascon-128a, and Ascon-80pq. In this paper, we study the resistance of the Ascon~family against conditional cube attacks in nonce-misuse setting, and present new state- and key-recovery attacks. Our attack recovers the full state...

A ring signature scheme allows a group member to generate a signature on behalf of the whole group, while the verifier can not tell who computed this signature. However, most predecessors do not guarantee security from the secret key leakage of signers. In 2002, Anderson proposed the forward security mechanism to reduce the effect of such leakage. In this paper, we construct the first lattice-based ring signature scheme with forward security. Our scheme combines the binary tree and lattice...

Recently, new ideas to build homomorphic noise-free encryption schemes have been proposed. The starting point of these schemes deals with private-key encryption schemes whose secret key is a rational function. By construction, these schemes are not homomorphic. To get homomorphic properties, nonlinear homomorphic operators are derived from the secret key. In this paper, we adopt the same approach to build a HE. We obtain a multivariate encryption scheme in the sense that the knowledge...

We present a rather generic backdoor mechanism that can be applied to many LWE-like public-key cryptosystems. Our construction manipulates the key generation algorithm of such schemes in a way that allows a malicious adversary in possession of secret backdoor information to recover generated secret keys from corresponding public keys. To any user of the cryptosystem however, the output of our backdoored key generation is indistinguishable from output of the legitimate key generation...

We propose a novel variant of functional encryption which supports ciphertext updates, dubbed ciphertext-updatable functional encryption (CUFE). Such a feature further broadens the practical applicability of the functional-encryption paradigm and allows for fine-grained access control even after a ciphertext is generated. Updating ciphertexts is carried out via so-called update tokens which a dedicated party can use to convert ciphertexts. However, allowing update tokens requires some care...

We investigate a new class of fault-injection attacks against the CSIDH family of cryptographic group actions. Our disorientation attacks effectively flip the direction of some isogeny steps. We achieve this by faulting a specific subroutine, connected to the Legendre symbol or Elligator computations performed during the evaluation of the group action. These subroutines are present in almost all known CSIDH implementations. Post-processing a set of faulty samples allows us to infer...

CSI-FiSh is one of the most efficient isogeny-based signature schemes, which is proven to be secure in the Quantum Random Oracle Model (QROM). However, there is a bottleneck in CSI-FiSh in the threshold setting, which is that its public key needs to be generated by using $k-1$ secret keys. This leads to very inefficient threshold key generation protocols and also forces the parties to store $k-1$ secret shares. We present CSI-SharK, a new variant of $\textit{CSI}$-FiSh that has more...

K-Cipher is an ultra-low latency block cipher with variable-length parameters designed by Intel Labs. In this work, we analyze the security of K-Cipher and propose a differential cryptanalysis attack with the complexity of $2^{29.7}$ for a variant of K-Cipher with state size $n=24$ bits state and block size $m=8$ bits. Our attack recovers the secret key and secret randomizer values with a total length of 240 bits in $\sim 30$ minutes on a standard desktop machine. We show that it is...

We propose the signature scheme Hawk, a concrete instantiation of proposals to use the Lattice Isomorphism Problem (LIP) as a foundation for cryptography that focuses on simplicity. This simplicity stems from LIP, which allows the use of lattices such as $\mathbb{Z}^n$ , leading to signature algorithms with no floats, no rejection sampling, and compact precomputed distributions. Such design features are desirable for constrained devices, and when computing signatures inside FHE or MPC. The...

It has been forty years since the TCP/IP protocol blueprint, which is the core of modern worldwide Internet, was published. Over this long period, technology has made rapid progress. These advancements are slowly putting pressure and placing new demands on the underlying network architecture design. Therefore, there was a need for innovations that can handle the increasing demands of new technologies like IoT while ensuring secrecy and privacy. It is how Named Data Networking (NDN) came into...

Resistance to key misuse attacks is a vital property for key encapsulation mechanisms（KEMs）in NIST-PQC standardization process. In key mismatch attack, the adversary recovers reused secret key with the help of an oracle $\mathcal{O}$ that indicates whether the shared key matches or not. Key mismatch attack is more powerful when fewer oracle queries are required. A series of works tried to reduce query times, Qin et al. [AISACRYPT 2021] gave a systematic approach to finding lower bound of...

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...