What a lovely hat

Multi-Authority Functional Encryption ($\mathsf{MA}$-$\mathsf{FE}$) [Chase, TCC'07; Lewko-Waters, Eurocrypt'11; Brakerski et al., ITCS'17] is a popular generalization of functional encryption ($\mathsf{FE}$) with the central goal of decentralizing the trust assumption from a single central trusted key authority to a group of multiple, independent and non-interacting, key authorities. Over the last several decades, we have seen tremendous advances in new designs and constructions for...

The CKKS scheme is traditionally recognized for approximate homomorphic encryption of real numbers, but BLEACH (Drucker et al., JoC 2024) extends its capabilities to handle exact computations on binary or small integer numbers. Despite this advancement, BLEACH's approach of simulating XOR gates via $(a-b)^2$ incurs one multiplication per gate, which is computationally expensive in homomorphic encryption. To this end, we introduce XBOOT, a new framework built upon BLEACH's blueprint but...

Hybrid Homomorphic Encryption (HHE) is considered a promising solution for key challenges that emerge when adopting Homomorphic Encryption (HE). In cases such as communication and computation overhead for clients and storage overhead for servers, it combines symmetric cryptography with HE schemes. However, despite a decade of advancements, enhancing HHE usability, performance, and security for practical applications remains a significant stake. This work contributes to the field by...

We revisit a basic building block in the endeavor to migrate to post-quantum secure cryptography, Key Encapsulation Mechanisms (KEMs). KEMs enable the establishment of a shared secret key, using only public communication. When targeting chosen-ciphertext security against quantum attackers, the go-to method is to design a Public-Key Encryption (PKE) scheme and then apply a variant of the PKE-to-KEM conversion known as the Fujisaki-Okamoto (FO) transform, which we revisit in this work....

Side-channel analysis (SCA) does not aim at the algorithm's weaknesses but rather its implementations. The rise of machine learning (ML) and deep learning (DL) is giving adversaries advanced capabilities to perform stealthy attacks. In this paper, we propose DL-SCADS, a DL-based approach along with signal decomposition techniques to leverage the power of secret key extraction from post-silicon EM/power side-channel traces. We integrate previously proven effective ideas of model ensembling...

Side-channel attacks exploit information leaked through non-primary channels, such as power consumption, electromagnetic emissions, or timing, to extract sensitive data from cryptographic devices. Over the past three decades, side-channel analysis has evolved into a mature research field with well-established methodologies for analyzing standard cryptographic algorithms like the Advanced Encryption Standard (AES). However, the integration of side-channel analysis with formal methods remains...

The evasive LWE assumption, proposed by Wee [Eurocrypt'22 Wee] for constructing a lattice-based optimal broadcast encryption, has shown to be a powerful assumption, adopted by subsequent works to construct advanced primitives ranging from ABE variants to obfuscation for null circuits. However, a closer look reveals significant differences among the precise assumption statements involved in different works, leading to the fundamental question of how these assumptions compare to each other. In...

In many lightweight cryptography applications, low area and latency are required for efficient implementation. The gate count in the cipher and the circuit depth must be low to minimize these two metrics. Many optimization strategies have been developed for the linear layer, led by the Boyar-Peralta (BP) algorithm. The Advanced Encryption Standard (AES) has been a focus of extensive research in this area. However, while the linear layer uses only XOR gates, the S-box, which is an essential...

The hardness of lattice problems offers one of the most promising security foundations for quantum-safe cryptography. Basic schemes for public key encryption and digital signatures are already close to standardization at NIST and several other standardization bodies, and the research frontier has moved on to building primitives with more advanced privacy features. At the core of many such primi- tives are zero-knowledge proofs. In recent years, zero-knowledge proofs for (and using)...

Succinct randomized encodings allow encoding the input $x$ of a time-$t$ uniform computation $M(x)$ in sub-linear time $o(t)$. The resulting encoding $\tilde{x}$ allows recovering the result of the computation $M(x)$, but hides any other information about $x$. These encodings have powerful applications, including time-lock puzzles, reducing communication in MPC, and bootstrapping advanced encryption schemes. Until not long ago, the only known constructions were based on...

We construct the first multi-input functional encryption (MIFE) and indistinguishability obfuscation (iO) schemes for pseudorandom functionalities, where the output of the functionality is pseudorandom for every input seen by the adversary. Our MIFE scheme relies on LWE and evasive LWE (Wee, Eurocrypt 2022 and Tsabary, Crypto 2022) for constant arity functions, and a strengthening of evasive LWE for polynomial arity. Thus, we obtain the first MIFE and iO schemes for a nontrivial...

One of the most popular techniques to prove adaptive security of identity-based encryptions (IBE) and verifiable random functions (VRF) is the partitioning technique. Currently, there are only two methods to relate the adversary's advantage and runtime $(\epsilon, {\sf T})$ to those of the reduction's ($\epsilon_{\sf proof}, {\sf T}_{\sf proof}$) using this technique: One originates to Waters (Eurocrypt 2005) who introduced the famous artificial abort step to prove his IBE, achieving...

Attribute-based encryption (ABE) is a powerful primitive that has found applications in important real-world settings requiring access control. Compared to traditional public-key encryption, ABE has established itself as a considerably more complex primitive that is additionally less efficient to implement. It is therefore paramount that the we can simplify the design of ABE schemes that are efficient, provide strong security guarantees, minimize the complexity in their descriptions and...

Identity-based matchmaking encryption (IB-ME) is an advanced encryption scheme that enables a sender and a receiver to specify each of identity. In general, from the aspect of abilities for adversaries, we have two flavors of security for encryption schemes chosen plaintext attacks (CPA) security and chosen ciphertext attacks (CCA) security. Compared to CPA security, CCA security can capture active adversaries, then it has been recognized as a desirable one. In this paper, we investigate...

For more than two decades, pairings have been a fundamental tool for designing elegant cryptosystems, varying from digital signature schemes to more complex privacy-preserving constructions. However, the advancement of quantum computing threatens to undermine public-key cryptography. Concretely, it is widely accepted that a future large-scale quantum computer would be capable to break any public-key cryptosystem used today, rendering today's public-key cryptography obsolete and mandating the...

Strike-lists are a common technique for rollback and replay prevention in protocols that require that clients remain anonymous or that their current position in a state machine remain confidential. Strike-lists are heavily used in anonymous credentials, e-cash schemes, and trusted execution environments, and are widely deployed on the web in the form of Privacy Pass (PoPETS '18) and Google Private State Tokens. In such protocols, clients submit pseudorandom tokens associated with each...

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...

The field of Fully Homomorphic Encryption (FHE) has seen many theoretical and computational advances in recent years, bringing the technology closer to practicality than ever before. For this reason, practitioners from neighbouring fields such as machine learning have sought to understand FHE to provide privacy to their work. Unfortunately, selecting secure and efficient parameters in FHE is a daunting task due to the many interdependencies between the parameters involved. In this work, we...

Registered attribute-based encryption (Reg-ABE), introduced by Hohenberger et al. (Eurocrypt’23), emerges as a pivotal extension of attribute-based encryption (ABE), aimed at mitigating the key-escrow problem. Although several Reg-ABE schemes with black-box use of cryptography have been proposed so far, there remains a significant gap in the class of achievable predicates between vanilla ABE and Reg-ABE. To narrow this gap, we propose a modular framework for constructing Reg-ABE schemes for a...

Message Authentication Codes (MACs) are ubiquitous primitives deployed in multiple flavors through standards such as HMAC, CMAC, GMAC, LightMAC, and many others. Its versatility makes it an essential building block in applications necessitating message authentication and integrity checks, in authentication protocols, authenticated encryption schemes, or as a pseudorandom or key derivation function. Its usage in this variety of settings makes it susceptible to a broad range of attack...

Almost perfect nonlinear (in brief, APN) functions are vectorial functions $F:\mathbb F_2^n\rightarrow \mathbb F_2^n$ playing roles in several domains of information protection, at the intersection of computer science and mathematics. Their definition comes from cryptography and is also related to coding theory. When they are used as substitution boxes (S-boxes, which are the only nonlinear components in block ciphers), APN functions contribute optimally to the resistance against...

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)...

To introduce a post-quantum-secure encryption scheme specifically for use in flight-computers, we used avionics’ module-isolation methods to wrap a recent encryption standard (HPKE – Hybrid Public Key Encryption) within a software partition. This solution proposes an upgrade to HPKE, using quantum-resistant ciphers (Kyber/ML-KEM and Dilithium/ML-DSA) redundantly alongside well-established ciphers, to achieve post-quantum security. Because cryptographic technology can suddenly become...

FUTURE is a recently proposed lightweight block cipher that achieved a remarkable hardware performance due to careful design decisions. FUTURE is an Advanced Encryption Standard (AES)-like Substitution-Permutation Network (SPN) with 10 rounds, whose round function consists of four components, i.e., SubCell, MixColumn, ShiftRow and AddRoundKey. Unlike AES, it is a 64-bit-size block cipher with a 128-bit secret key, and the state can be arranged into 16 cells. Therefore, the operations of...

Threshold signatures have recently seen a renewed interest due to applications in cryptocurrency while NIST has released a call for multi-party threshold schemes, with a deadline for submission expected for the first half of 2025. So far, all lattice-based threshold signatures requiring less than two-rounds are based on heavy tools such as (fully) homomorphic encryption (FHE) and homomorphic trapdoor commitments (HTDC). This is not unexpected considering that most efficient two-round...

The Advanced Encryption Standard (AES) is one of the most commonly used and analyzed encryption algorithms. In this work, we present new combinations of some prominent attacks on AES, achieving new records in data requirements among attacks, utilizing only $2^4$ and $2^{16}$ chosen plaintexts (CP) for 6-round and 7-round AES-192/256 respectively. One of our attacks is a combination of a meet-in-the-middle (MiTM) attack with a square attack mounted on 6-round AES-192/256 while ...

Fully Homomorphic Encryption (FHE) is a cryptographic primitive that allows performing arbitrary operations on encrypted data. Since the conception of the idea in [RAD78], it was considered a holy grail of cryptography. After the first construction in 2009 [Gen09], it has evolved to become a practical primitive with strong security guarantees. Most modern constructions are based on well-known lattice problems such as Learning with Errors (LWE). Besides its academic appeal, in recent years...

A Password-Authenticated Key Exchange (PAKE) protocol allows two parties to agree upon a cryptographic key, in the setting where the only secret shared in advance is a low-entropy password. The standard security notion for PAKE is in the Universal Composability (UC) framework. In recent years there have been a large number of works analyzing the UC-security of Encrypted Key Exchange (EKE), the very first PAKE protocol, and its One-encryption variant (OEKE), both of which compile an...

We present a new method for efficient look-up table (LUT) evaluation in homomorphic encryption (HE), based on Ring-LWE-based HE schemes, including both integer-message schemes such as Brakerski-Gentry-Vaikuntanathan (BGV) and Brakerski/Fan-Vercauteren (BFV), and complex-number-message schemes like the Cheon-Kim-Kim-Song (CKKS) scheme. Our approach encodes bit streams into codewords and translates LUTs into low-degree multivariate polynomials, allowing for the simultaneous evaluation of...

The advancements in information technology have made the Advanced Encryption Standard (AES) and the PRESENT cipher indispensable in ensuring data security and facilitating private transactions. AES is renowned for its flexibility and widespread use in various fields, while the PRESENT cipher excels in lightweight cryptographic situations. This paper delves into a dual examination of the Key Scheduling Algorithms (KSAs) of AES and the PRESENT cipher, which play a crucial role in generating...

Threshold signatures improve both availability and security of digital signatures by splitting the signing key into $N$ shares handed out to different parties. Later on, any subset of at least $T$ parties can cooperate to produce a signature on a given message. While threshold signatures have been extensively studied in the pre-quantum setting, they remain sparse from quantum-resilient assumptions. We present the first efficient lattice-based threshold signatures with signature size 13...

The prevailing ciphers rely on the weak assumption that their attacker is not smarter than expected by their designers. The resultant crypto ecology favors the cryptographic powerhouses, and hinders cyber freedom, cyber privacy and cyber democracy. This weakness can be remedied by using the gold standard of cryptography -- One Time Pad, OTP. Alas, it comes with a prohibitive cost of a key as long as the message it encrypts. When the stakes are high enough users pay this high price because...

Artificial intelligence (AI) is a modern technology that allows plenty of advantages in daily life, such as predicting weather, finding directions, classifying images and videos, even automatically generating code, text, and videos. Other essential technologies such as blockchain and cybersecurity also benefit from AI. As a core component used in blockchain and cybersecurity, cryptography can benefit from AI in order to enhance the confidentiality and integrity of cyberspace. In this...

Driven by the open problem raised by Hofheinz and Kiltz (Journal of Cryptology, 2012), we study the formalization of lattice-based programmable hash function (PHF), and give three types of concrete constructions by using several techniques such as a novel combination of cover-free sets and lattice trapdoors. Under the Inhomogeneous Small Integer Solution (ISIS) assumption, we show that any (non-trivial) lattice-based PHF is a collision-resistant hash function, which gives a direct...

Common block ciphers like AES specified by the NIST or KASUMI (A5/3) of GSM are extensively utilized by billions of individuals globally to protect their privacy and maintain confidentiality in daily communications. However, these ciphers lack comprehensive security proofs against the vast majority of known attacks. Currently, security proofs are limited to differential and linear attacks for both AES and KASUMI. For instance, the consensus on the security of AES is not based on formal...

With the advancement of quantum computers, it has been demonstrated that Shor's algorithm enables public key cryptographic attacks to be performed in polynomial time. In response, NIST conducted a Post-Quantum Cryptography Standardization competition. Additionally, due to the potential reduction in the complexity of symmetric key cryptographic attacks to square root with Grover's algorithm, it is increasingly challenging to consider symmetric key cryptography as secure. In order to establish...

Identity-based matchmaking encryption (IB-ME) [Ateniese et al. Crypto 2019] allows users to communicate privately in an anonymous and authenticated manner. After the seminal paper by Ateniese et al., a lot of work has been done on the security and construction of IB-ME. In this work, we revisit the security definitions of IB-ME and provide improved constructions of it. First, we classify the existing security notions of IB-ME, systematically categorizing privacy into three categories (CPA,...

IoT devices collect privacy-sensitive data, e.g., in smart grids or in medical devices, and send this data to cloud servers for further processing. In order to ensure confidentiality as well as authenticity of the sensor data in the untrusted cloud environment, we consider a transciphering scenario between embedded IoT devices and multiple cloud servers that perform secure multi-party computation (MPC). Concretely, the IoT devices encrypt their data with a lightweight symmetric cipher and...

In this paper, we show that it is impossible to construct a public key encryption scheme (PKE) from a ring signature scheme in a black-box fashion in the standard model. Such an impossibility is highly non-trivial because, to the best of our knowledge, known generic constructions of ring signature scheme are based on public key cryptosystems or in the random oracle model. Technically, we introduce a new cryptographic primitive named indistinguishable multi-designated verifiers signature...

We initiate the study of witness authenticating NIZK proof systems (waNIZKs), in which one can use a witness $w$ of a statement $x$ to identify whether a valid proof for $x$ is indeed generated using $w$. Such a new identification functionality enables more diverse applications, and it also puts new requirements on soundness that: (1) no adversary can generate a valid proof that will not be identified by any witness; (2) or forge a proof using some valid witness to frame others. To work...

In oblivious finite automata evaluation, one party holds a private automaton, and the other party holds a private string of characters. The objective is to let the parties know whether the string is accepted by the automaton or not, while keeping their inputs secret. The applications include DNA searching, pattern matching, and more. Most of the previous works are based on asymmetric cryptographic primitives, such as homomorphic encryption and oblivious transfer. These primitives are...

Data security and secrecy from unwanted applications are the subjects of the science known as cryptography. The advanced encryption standard algorithm is the most used and secure algorithm to encrypt data. The AES algorithm is based on the symmetric algorithm and uses a single key to encrypt and decrypt data. The AES algorithm uses 128 bits length of plain text with 128 bits, 192 bits, or 256 bits key size to encrypt data. Latin script uses ASCII codes, and a single byte represents each...

Since the pioneering work of Gentry, Halevi, and Smart in 2012, the state of the art on transciphering has moved away from work on AES to focus on new symmetric algorithms that are better suited for a homomorphic execution. Yet, with recent advances in homomorphic cryptosystems, the question arises as to where we stand today. Especially since AES execution is the application that may be chosen by NIST in the FHE part of its future call for threshold encryption. In this paper, we propose an...

Constructing advanced cryptographic primitives such as obfuscation or broadcast encryption from standard hardness assumptions in the post quantum regime is an important area of research, which has met with limited success despite significant effort. It is therefore extremely important to find new, simple to state assumptions in this regime which can be used to fill this gap. An important step was taken recently by Wee (Eurocrypt '22) who identified two new assumptions from lattices, namely...

With the increased use of data and communication through the internet and the abundant misuse of personal data by many organizations, people are more sensitive about their privacy. Privacy-preserving computation is becoming increasingly important in this era. Functional encryption allows a user to evaluate a function on encrypted data without revealing sensitive information. Most implementations of functional encryption schemes are too time-consuming for practical use. Mera et al. first...

In the last decade, zero-knowledge proof of knowledge protocols have been extensively studied to achieve active security of various cryptographic protocols. However, the existing solutions simply seek zero-knowledge for both message and randomness, which is an overkill in many applications since protocols may remain secure even if some information about randomness is leaked to the adversary. We develop this idea to improve the state-of-the-art proof of knowledge protocols for RLWE-based...

The Meet-in-the-Middle (MITM) attack is one of the most powerful cryptanalysis techniques, as seen by its use in preimage attacks on MD4, MD5, Tiger, HAVAL, and Haraka-512 v2 hash functions and key recovery for full-round KTANTAN. An efficient approach to constructing MITM attacks is automation, which refers to modeling MITM characteristics and objectives into constraints and using optimizers to search for the best attack configuration. This work focuses on the simplification and renovation...

A thread of physical attacks that try to obtain secret information from cryptographic modules has been of academic and practical interest. One of the concerns is determining its efficiency, e.g., the number of attack trials to recover the secret key. However, the accurate estimation of the attack efficiency is generally expensive because of the complexity of the physical attack on a cryptographic algorithm. Based on this background, in this study, we propose a new abstraction model for...

Over the years, a large number of attacks have been proposed against substitution boxes used in symmetric ciphers such as differential attacks, linear attacks, algebraic attacks, etc. In the Advanced Encryption Standard (AES) Block cipher, the substitution box is the only nonlinear component and thus it holds the weight of the cipher. This basically means that if an attacker is able to mount a successful attack on the substitution box of AES, the cipher is compromised. This research work...

We introduce the notion of public key encryption with secure key leasing (PKE-SKL). Our notion supports the leasing of decryption keys so that a leased key achieves the decryption functionality but comes with the guarantee that if the quantum decryption key returned by a user passes a validity test, then the user has lost the ability to decrypt. Our notion is similar in spirit to the notion of secure software leasing (SSL) introduced by Ananth and La Placa (Eurocrypt 2021) but captures...

Encrypting too much data using the same key is a bad practice from a security perspective. Hence, it is customary to perform re-keying after a given amount of data is transmitted. While in many cases, the re-keying is done using a fresh execution of some key exchange protocol (e.g., in IKE or TLS), there are scenarios where internal re-keying, i.e., without exchange of information, is performed, mostly due to performance reasons. Originally suggested by Abdalla and Bellare, there are...

In this paper, we examine the algebraic XSL attack on the Advanced Encryption Standard (AES). We begin with a brief introduction and we present an overview of AES, then, in Section 3, we present the algebraic attack on ciphers like AES, following with the XL and XSL algorithms in Section 4 and Section 5. Then, we present the XSL first and second attacks, also their aplicability on BES. We see how and if the algorithm has been improved since it firstly appeared. We conclude with Section 10.

The goals of cryptography are achieved using mathematically strong crypto-algorithms, which are adopted for securing data and communication. Even though the algorithms are mathematically secure, the implementation of these algorithms may be vulnerable to side-channel attacks such as timing and power analysis attacks. One of the effective countermeasures against such attacks is Threshold Implementation(TI). However, TI realization in crypto-device introduces hardware complexity, so it...

Previous studies on fault analysis have demonstrated promising potential in compromising cryptographic security. However, these fault analysis methods are limited in practical impact due to methodological constraints and the substantial requirement of faulty information such as correct and faulty ciphertexts. Additionally, while deep learning techniques have been widely applied to side-channel analysis (SCA) in recent years and have shown superior performance compared with traditional...

Optimizing the quantum circuit for implementing Advanced Encryption Standard (AES) is crucial for estimating the necessary resources in attacking AES by Grover algorithm. Previous studies have reduced the number of qubits required for the quantum circuits of AES-128/-192/-256 from 984/1112/1336 to 270/334/398, which is close to the optimal value of 256/320/384. It becomes a challenging task to further optimize them. Aiming at this task, we find a method about how the quantum circuit of AES...

Non-committing encryption (NCE) is an advanced form of public-key encryption which guarantees the security of a Multi-Party Computation (MPC) protocol in the presence of an adaptive adversary. Brakerski et al. (TCC 2020) recently proposed an intermediate notion, termed Packed Encryption with Partial Equivocality (PEPE), which implies NCE and preserves the ciphertext rate (up to a constant factor). In this work, we propose three new constructions of rate-1 PEPE based on standard assumptions....

Continuous Group Key Agreement (CGKA) is the basis of modern Secure Group Messaging (SGM) protocols. At a high level, a CGKA protocol enables a group of users to continuously compute a shared (evolving) secret while members of the group add new members, remove other existing members, and perform state updates. The state updates allow CGKA to offer desirable security features such as forward secrecy and post-compromise security. CGKA is regarded as a practical primitive in the...

We present the first fully collusion resistant traitor tracing (TT) scheme for identity-based inner product functional encryption (IBIPFE) that directly traces user identities through an efficient tracing procedure. We name such a scheme as embedded identity traceable IBIPFE (EI-TIBIPFE), where secret keys and ciphertexts are computed for vectors u and v respectively. Additionally, each secret key is associated with a user identification information tuple (i , id, gid) that specifies user...

Multiplicative Complexity (MC) is defined as the minimum number of AND gates required to implement a function with a circuit over the basis AND, XOR, NOT. This complexity measure is relevant for many advanced cryptographic protocols such as fully homomorphic encryption, multi-party computation, and zero-knowledge proofs, where processing AND gates is more expensive than processing XOR gates. Although there is no known asymptotically efficient technique to compute the MC of a random Boolean...

Motivated by several new and natural applications, we initiate the study of multi-input predicate encryption (${\sf miPE}$) and further develop multi-input attribute based encryption (${\sf miABE}$). Our contributions are: 1. Formalizing Security: We provide definitions for ${\sf miABE}$ and ${\sf miPE}$ in the {symmetric} key setting and formalize security in the standard indistinguishability (IND) paradigm, against unbounded collusions. 2. Two-input ${\sf ABE}$ for ${\sf NC}_1$...

We introduce Multimodal Private Signature (MPS) - an anonymous signature system that offers a novel accountability feature: it allows a designated opening authority to learn some partial information $\mathsf{op}$ about the signer's identity $\mathsf{id}$, and nothing beyond. Such partial information can flexibly be defined as $\mathsf{op} = \mathsf{id}$ (as in group signatures), or as $\mathsf{op} = \mathbf{0}$ (like in ring signatures), or more generally, as $\mathsf{op} =...

Fully Homomorphic Encryption (FHE) is a powerful cryptographic primitive that enables performing computations over encrypted data without having access to the secret key. We introduce OpenFHE, a new open-source FHE software library that incorporates selected design ideas from prior FHE projects, such as PALISADE, HElib, and HEAAN, and includes several new design concepts and ideas. The main new design features can be summarized as follows: (1) we assume from the very beginning that all...

Blockchain protocols have revolutionized the way individuals and devices can interact and transact over the internet. More recently, a trend has emerged to harness blockchain technology as a catalyst to enable advanced security features in distributed applications, in particular fairness. However, the tools employed to achieve these security features are either resource wasteful (e.g., time-lock primitives) or only efficient in theory (e.g., witness encryption). We present McFly, a protocol...

The Internet of Things (IoT) has brought new ways for humans and machines to communicate with each other over the internet. Though sensor-driven devices have largely eased our everyday lives, most IoT infrastructures have been suffering from security challenges. Since the emergence of IoT, lightweight block ciphers have been a better option for intelligent and sensor-based applications. When public-key infrastructure dominates worldwide, the symmetric key encipherment such as Advanced...

Predictable arguments introduced by Faonio, Nielsen and Venturi (PKC17) are private-coin argument systems where the answer of the prover can be predicted in advance by the verifier. In this work, we study predictable arguments with additional privacy properties. While the authors in [PKC17] showed compilers for transforming PAs into PAs with zero-knowledge property, they left the construction of witness indistinguishable predictable arguments (WI-PA) in the plain model as an open problem. In...

Side-channel attacks exploit a physical observable originating from a cryptographic device in order to extract its secrets. Many practically relevant advances in the field of side-channel analysis relate to security evaluations of cryptographic functions and devices. Accordingly, many metrics have been adopted or defined to express and quantify side-channel security. These metrics can relate to one another, but also conflict in terms of effectiveness, assumptions and security goals. In...

Nowadays, together with stormy technology advancement, billions of interconnected devices are constantly collecting data around us. In that fashion, privacy protection has become a major concern. The data must be in encrypted form before being stored on the cloud servers. As a result, the cloud servers are unable to perform calculations on en- crypted data, such as searching and matching keywords. In the PKE- MET setting, a cloud server can perform an equality test on a number of ciphertexts...

Continuous Group Key Agreement (CGKA) -- or Group Ratcheting -- lies at the heart of a new generation of scalable End-to-End secure (E2E) cryptographic multi-party applications. One of the most important (and first deployed) CGKAs is ITK which underpins the IETF's upcoming Messaging Layer Security E2E secure group messaging standard. To scale beyond the group sizes possible with earlier E2E protocols, a central focus of CGKA protocol design is to minimize bandwidth requirements (i.e....

A number of arithmetization-oriented ciphers emerge for use in advanced cryptographic protocols such as secure multi-party computation (MPC), fully homomorphic encryption (FHE) and zero-knowledge proofs (ZK) in recent years. The standard block ciphers like AES and the hash functions SHA2/SHA3 are proved to be efficient in software and hardware but not optimal to use in this field, for this reason, new kind of cryptographic primitives were proposed recently. However, unlike traditional ones,...

Deep Learning Side-Channel Attacks (DLSCAs) have become a realistic threat to implementations of cryptographic algorithms, such as Advanced Encryption Standard (AES). By utilizing deep-learning models to analyze side-channel measurements, the attacker is able to derive the secret key of the cryptographic alrgorithm. However, when traces have multiple leakage intervals for a specific attack point, the majority of existing works train neural networks on these traces directly, without a...

In this work we resolve the open problem raised by Prabhakaran and Rosulek at CRYPTO 2007, and present the first anonymous, rerandomizable, Replayable-CCA (RCCA) secure public-key encryption scheme. This solution opens the door to numerous privacy-oriented applications with a highly desired RCCA security level. At the core of our construction is a non-trivial extension of smooth projective hash functions (Cramer and Shoup, EUROCRYPT 2002), and a modular generic framework developed for...

Fully homomorphic encryption (FHE) is one of the prospective tools for privacy-preserving machine learning (PPML), and several PPML models have been proposed based on various FHE schemes and approaches. Although the FHE schemes are known as suitable tools to implement PPML models, previous PPML models on FHE such as CryptoNet, SEALion, and CryptoDL are limited to only simple and non-standard types of machine learning models. These non-standard machine learning models are not proven efficient...

Graphics processing units (GPUs) are specially designed for parallel applications and perform parallel operations much faster than central processing units (CPUs). In this work, we focus on the performance of the Advanced Encryption Standard (AES) on GPUs. We present optimizations which remove bank conflicts in shared memory accesses and provide 878.6 Gbps throughput for AES-128 encryption on an RTX 2070 Super, which is equivalent to 4.1 Gbps per Watt. Our optimizations provide more than...

Block ciphers such as the Advanced Encryption Standard (Rijndael) are used extensively in practice, yet our understanding of their security continues to be highly incomplete. This paper promotes and continues a research program aimed at *proving* the security of block ciphers against important and well-studied classes of attacks. In particular, we initiate the study of (almost) $t$-wise independence of concrete block-cipher construction paradigms such as substitution-permutation networks and...

This paper proposes a new ultra lightweight cipher RAGHAV. RAGHAV is a Substitution-Permutation (SP) network, which operates on 64 bit plaintext and supports a 128/80 bit key scheduling. It needs only 994.25 GEs by using 0.13µm ASIC technology for a 128 bit key scheduling. It also needs less memory i.e. 2204 bytes of FLASH memory , which is less as compared to all existing S-P network lightweight ciphers. This paper presents a complete security analysis of RAGHAV, which includes basic...

The United Kingdom (UK) government is considering advanced primitives such as identity-based encryption (IBE) for adoption as they transition their public-safety communications network from TETRA to an LTE-based service. However, the current LTE standard relies on elliptic-curve-based IBE, which will be vulnerable to quantum computing attacks, expected within the next 20-30 years. Lattices can provide quantum-safe alternatives for IBE. These schemes have shown promising results in terms of...

Advanced Encryption Standard used with Galois Counter Mode, mode of operation is one of the the most secure modes to use the AES. This paper represents an overview of the AES modes focusing the AES-GCM mode and its particularities. Moreover, after a detailed analysis of the possibility of enhancement for the encryption and authentication phase, a method of generating custom encryption schemes based on GF($2^8$) irreducible polynomials different from the standard polynomial used by the...

The Advanced Encryption Standard (AES) is the most widely used symmetric encryption algorithm. Its security is mainly based on the structure of the S-box. In this paper, we present a new way to create S-boxes for AES and exhibit an S-box with improved cryptographic properties such as Bit Independence Criterion (BIC), periodicity, algebraic complexity, Strict Avalanche Criterion (SAC) and Distance to SAC.

Public key cryptography is an indispensable component used in almost all of our present day digital infrastructure. However, most if not all of it is predominantly built upon hardness guarantees of number theoretic problems that can be broken by large scale quantum computers in the future. Sensing the imminent threat from continued advances in quantum computing, NIST has recently initiated a global level standardization process for quantum resistant public-key cryptographic primitives such...

The Cheon-Kim-Kim-Song (CKKS) homomorphic encryption scheme is currently the most efficient method to perform approximate homomorphic computations over real and complex numbers. Although the CKKS scheme can already be used to achieve practical performance for many advanced applications, e.g., in machine learning, its broader use in practice is hindered by several major usability issues, most of which are brought about by relatively high approximation errors and the complexity of dealing with...

Although large numbers of hardware and software implementations have been proposed to accelerate lattice-based cryptography, Saber, a module-LWR-based algorithm, which has advanced to second round of the NIST standardization process, has not been adequately supported by the current solutions. Based on these motivations, a high-performance crypto-processor is proposed based on an algorithm-hardware co-design in this paper. First, a hierarchical Karatsuba calculating framework, a...

Learning parity with noise (LPN) is a notorious (average-case) hard problem that has been well studied in learning theory, coding theory and cryptography since the early 90's. It further inspires the Learning with Errors (LWE) problem [Regev, STOC 2005], which has become one of the central building blocks for post-quantum cryptography and advanced cryptographic primitives. Unlike LWE whose hardness can be reducible from worst-case lattice problems, no corresponding worst-case hardness...

The technological advancements of the digital era paved the way for the facilitation of electronic voting (e-voting) in the promise of efficiency and enhanced security. In standard e-voting designs, the tally process is assigned to a committee of designated entities called talliers. Naturally, the security analysis of any e-voting system with tallier designation hinges on the assumption that a subset of the talliers follows the execution guidelines and does not attempt to breach...

In modern ciphers of commercial computer cryptography 4-bit crypto substitution boxes or 4-bit crypto S-boxes are of utmost importance since the late sixties. Since then the 4 bit Boolean functions (BFs) are proved to be the best tool to generate the said 4-bit crypto S-boxes. In this paper the crypto related properties of the 4-bit BFs such as the algebraic normal form (ANF) of the 4-bit BFs, the balancedness, the linearity, the nonlinearity, the affinity and the non-affinity of the 4-bit...

The recent advances and attention to quantum computing have raised serious security concerns among IT professionals. The ability of a quantum computer to efficiently solve (elliptic curve) discrete logarithm, and integer factorization problems poses a threat to current public key exchange, encryption, and digital signature schemes. Consequently, in 2016 NIST initiated an open call for quantum-resistant crypto algorithms. This process, currently in its second round, has yielded nine...

We introduce an independent research project on symmetric cryptography with a focus on foreseeable industrial needs and higher post-quantum security compared to currently used symmetric algorithms. It was initiated by the independent IT-Security experts Kovac and Underhill. The result is the new symmetric cryptographic algorithm eAES, which is intended to be a stronger brother of the widely used Advanced Encryption Standard, the standardized version of the Rijndael algorithm. In this...

In November 2018, the HomomorphicEncryption.org consortium published the Homomorphic Encryption Security Standard. The Standard recommends several sets of Learning with Errors (LWE) parameters that can be selected by application developers to achieve a target security level \( \lambda \in \{128,192,256\} \). These parameter sets all involve a power-of-two dimension \( n \leq 2^{15} \), an error distribution of standard deviation \( \sigma \approx 3.19 \), and a secret whose coefficients are...

In this work we advance the study of leakage-resilient Authenticated Encryption with Associated Data (AEAD) and lay the theoretical groundwork for building such schemes from sponges. Building on the work of Barwell et al. (ASIACRYPT 2017), we reduce the problem of constructing leakage-resilient AEAD schemes to that of building fixed-input-length function families that retain pseudorandomness and unpredictability in the presence of leakage. Notably, neither property is implied by the other in...

Attribute-based encryption (ABE) is an advanced cryptographic tool and useful to build various types of access control systems. Toward the goal of making ABE more practical, we propose key-policy (KP) and ciphertext-policy (CP) ABE schemes, which first support unbounded sizes of attribute sets and policies with negation and multi-use of attributes, allow fast decryption, and are fully secure under a standard assumption, simultaneously. The proposed schemes are more expressive than previous...

Rapid advances in Internet technologies have fostered the emergence of the “software as a service” model for enterprise computing. The “Database as a Service” model provides users with the power to create, store, modify, and retrieve data from any location, as long as they have access to the Internet. As more and more datasets (including those containing private and sensitive data) are outsourced to remote / cloud storage providers, the data owner, firstly, needs to be certain of the...

Considering AES sub-steps that can be attacked with a small guess space, the most practicable is to target SubBytes of extremal rounds. For its contrast between candidates (non-linearity) and that the search space is reduced to 28 -sized blocks. But when such point of interests are not available, MixColumns may be considered but involve search spaces of 2^32 -sized blocks. This number of attacks to run being often considered as unrealistic to reach, published papers propose to attack using...

Concerning the side-channel attacks on Advanced Encryp- tion Standard, it seems that majority of studies focus on the lowest size: AES-128. Even when adaptable to higher sizes (AES-192 and AES-256), lots of state-of-the-art attacks see their complexity substantially raised. Indeed, it often requires to perform two consecutive dependent attacks. The first is similar to the one applied on AES-128, but a part of the key remains unknown and must be retrieved through a second attack...

This paper demonstrates how to achieve simulation-based strong attribute hiding against adaptive adversaries for predicate encryption (PE) schemes supporting expressive predicate families under standard computational assumptions in bilinear groups. Our main result is a simulation-based adaptively strongly partially-hiding PE (PHPE) scheme for predicates computing arithmetic branching programs (ABP) on public attributes, followed by an inner-product predicate on private attributes. This...

The technology of homomorphic encryption has improved rapidly in a few years. The cutting edge implementations are efficient enough to use in practical applications. Recently, Cheon et al. (ASIACRYPT'17) proposed a homomorphic encryption scheme which supports an arithmetic of approximate numbers over encryption. This scheme shows the current best performance in computation over the real numbers, but its implementation could not employ core optimization techniques based on the Residue Number...

The Noise Protocol Framework, introduced recently, allows for the design and construction of secure channel protocols by describing them through a simple, restricted language from which complex key derivation and local state transitions are automatically inferred. Noise "Handshake Patterns" can support mutual authentication, forward secrecy, zero round-trip encryption, identity hiding and other advanced features. Since the framework's release, Noise-based protocols have been adopted by...

Symbolic methods have been used extensively for proving security of cryptographic protocols in the Dolev-Yao model, and more recently for proving security of cryptographic primitives and constructions in the computational model. However, existing methods for proving security of cryptographic constructions in the computational model often require significant expertise and interaction, or are fairly limited in scope and expressivity. This paper introduces a symbolic approach for proving...

We study Authenticated Encryption with Associated Data (AEAD) from the viewpoint of composition in arbitrary (single-stage) environments. We use the indifferentiability framework to formalize the intuition that a good AEAD scheme should have random ciphertexts subject to decryptability. Within this framework, we can then apply the indifferentiability composition theorem to show that such schemes offer extra safeguards wherever the relevant security properties are not known, or cannot be...

Post-quantum cryptography has attracted much attention from worldwide cryptologists. However, most research works are related to public-key cryptosystem due to Shor's attack on RSA and ECC ciphers. At CRYPTO 2016, Kaplan et al. showed that many secret-key (symmetric) systems could be broken using a quantum period finding algorithm, which encouraged researchers to evaluate symmetric systems against quantum attackers. In this paper, we continue to study symmetric ciphers against quantum...

In modern as well as ancient ciphers of public key cryptography, substitution boxes find a permanent seat. Generation and cryptanalysis of 4-bit as well as 8-bit crypto S-boxes is of utmost importance in modern cryptography. In this paper, a detailed review of cryptographic properties of S-boxes has been illustrated. The generation of crypto S-boxes with 4-bit as well as 8-bit Boolean functions (BFs) and Polynomials over Galois field GF(p^q) has also been of keen interest of this paper. The...

This paper presents a secure cloud storage scheme based on hybrid cryptosystem, which consists of Elliptic Curve Cryptography (ECC), Advanced Encryption Standard (AES), and one-way hash function. Here, the data owner exports large volume of encrypted data to a cloud storage provider. The exported encrypted data is over-encrypted by the cloud storage provider, and the data is sent to the requesting user. An existing hybrid cryptosystem based dynamic key management scheme with hierarchical...