What a lovely hat

Garbled Circuits are essential building blocks in cryptography, and extensive research has explored their construction from both applied and theoretical perspectives. However, a challenge persists: While theoretically designed garbled circuits offer optimal succinctness--remaining constant in size regardless of the underlying circuit’s complexit--and are reusable for multiple evaluations, their concrete computational costs are prohibitively high. On the other hand, practically efficient...

Many foundational results in the literature of consensus follow the Dolev-Yao model (FOCS '81), which treats digital signatures as ideal objects with perfect correctness and unforgeability. However, no work has yet formalized an ideal signature scheme that is both suitable for this methodology and possible to instantiate, or a composition theorem that ensures security when instantiating it cryptographically. The Universal Composition (UC) framework would ensure composition if we could...

We study the (in)feasibility of quantum pseudorandom notions in a quantum analog of the random oracle model, where all the parties, including the adversary, have oracle access to the same Haar random unitary. In this model, we show the following: • (Unbounded-query secure) pseudorandom unitaries (PRU) exist. Moreover, the PRU construction makes two calls to the Haar oracle. • We consider constructions of PRUs making a single call to the Haar oracle. In this setting, we show that...

Oblivious Pseudorandom Functions (OPRFs) allow a client to evaluate a pseudorandom function (PRF) on her secret input based on a key that is held by a server. In the process, the client only learns the PRF output but not the key, while the server neither learns the input nor the output of the client. The arguably most popular OPRF is due to Naor, Pinkas and Reingold (Eurocrypt 2009). It is based on an Oblivious Exponentiation by the server, with passive security under the Decisional...

Quantum pseudorandom state generators (PRSGs) have stimulated exciting developments in recent years. A PRSG, on a fixed initial (e.g., all-zero) state, produces an output state that is computationally indistinguishable from a Haar random state. However, pseudorandomness of the output state is not guaranteed on other initial states. In fact, known PRSG constructions provably fail on some initial states. In this work, we propose and construct quantum Pseudorandom State Scramblers (PRSSs),...

Studies of vector oblivious linear evaluation (VOLE)-based zero-knowledge (ZK) protocols flourish in recent years. Such ZK protocols feature optimal prover computation and a flexibility for handling arithmetic circuits over arbitrary fields. However, most of them have linear communication, which constitutes a bottleneck for handling large statements in a slow network. The pioneer work AntMan (CCS'22), achieved sublinear communication for the first time within VOLE-based ZK, but lost the...

Garbled circuits are a powerful and important cryptographic primitive, introduced by Yao [FOCS 1986] for secure two-party computation. Beaver, Micali and Rogaway (BMR) [STOCS 1990] extended the garbled circuit technique to construct the first constant-round secure multiparty computation (MPC) protocol. In the BMR protocol, the garbled circuit size grows linearly and the online computation time grows quadratically with the number of parties. Previous solutions to avoid this relied on...

Transitioning from classically to quantum secure key agreement protocols may require to exchange fundamental components, for example, exchanging Diffie-Hellman-like key exchange with a key encapsulation mechanism (KEM). Accordingly, the corresponding security proof can no longer rely on the Diffie-Hellman assumption, thus invalidating the security guarantees. As a consequence, the security properties have to be re-proven under a KEM-based security notion. We initiate the study of the...

Common random string model is a popular model in classical cryptography. We study a quantum analogue of this model called the common Haar state (CHS) model. In this model, every party participating in the cryptographic system receives many copies of one or more i.i.d Haar random states. We study feasibility and limitations of cryptographic primitives in this model and its variants: - We present a construction of pseudorandom function-like states with security against computationally...

t-out-of-n threshold ring signature (TRS) is a type of anonymous signature designed for t signers to jointly sign a message while hiding their identities among n parties that include themselves. However, can TRS address those needs if one of the signers wants to revoke his signature or, additively, sign separately later? Can non-signers be revoked without compromising anonymity? Previous research has only discussed opposing situations. The present study introduces a novel property for...

We present a general framework for constructing attribute-based encryption (ABE) schemes for arbitrary function class based on lattices from two ingredients, i) a noisy linear secret sharing scheme for the class and ii) a new type of inner-product functional encryption (IPFE) scheme, termed *evasive* IPFE, which we introduce in this work. We propose lattice-based evasive IPFE schemes and establish their security under simple conditions based on variants of evasive learning with errors (LWE)...

Common random string model is a popular model in classical cryptography with many constructions proposed in this model. We study a quantum analogue of this model called the common Haar state model, which was also studied in an independent work by Chen, Coladangelo and Sattath (arXiv 2024). In this model, every party in the cryptographic system receives many copies of one or more i.i.d Haar states. Our main result is the construction of a statistically secure PRSG with: (a) the output...

In 1982, Yao introduced the problem of comparing two private values, thereby launching the study of protocols for secure multi-party computation (MPC). Since then, comparison protocols have undergone extensive study and found widespread applications. We survey state-of-the-art comparison protocols for an arbitrary number of parties, decompose them into smaller primitives and analyse their communication complexity under the usual assumption that the underlying MPC protocol does...

There are two popular ways to measure computational entropy in cryptography: (HILL) pseudoentropy and (Yao) incompressibility entropy. Both of these computational entropy notions are based on a natural intuition. - A random variable $X$ has $k$ bits of pseudoentropy if there exists a random variable $Y$ that has $k$ bits 'real' entropy and $Y$ is computationally indistinguishable from $X$. - A random variable $X$ has $k$ bits of incompressibility entropy if $X$ cannot be efficiently...

Threshold Implementation (TI) is a well-known Boolean masking technique that provides provable security against side-channel attacks. In the presence of glitches, the probing model was replaced by the so-called glitch-extended probing model which specifies a broader security framework. In CHES 2021, Shahmirzadi et al. introduced a general search method for finding first-order 2-share TI schemes without fresh randomness (under the presence of glitches) for a given encryption algorithm....

We introduce a new notion called ${\cal Q}$-secure pseudorandom isometries (PRI). A pseudorandom isometry is an efficient quantum circuit that maps an $n$-qubit state to an $(n+m)$-qubit state in an isometric manner. In terms of security, we require that the output of a $q$-fold PRI on $\rho$, for $ \rho \in {\cal Q}$, for any polynomial $q$, should be computationally indistinguishable from the output of a $q$-fold Haar isometry on $\rho$. By fine-tuning ${\cal Q}$, we recover many...

Although we have known about fully homomorphic encryption (FHE) from circular security assumptions for over a decade [Gentry, STOC '09; Brakerski–Vaikuntanathan, FOCS '11], there is still a significant gap in understanding related homomorphic primitives supporting all *unrestricted* polynomial-size computations. One prominent example is attribute-based encryption (ABE). The state-of-the-art constructions, relying on the hardness of learning with errors (LWE) [Gorbunov–Vaikuntanathan–Wee,...

Protocols for secure multi-party computation (MPC) supporting mixed-mode computation have found a lot of applications in recent years due to their flexibility in representing the function to be evaluated. However, existing mixed-mode MPC protocols are only practical for a small number of parties: they are either tailored to the case of two/three parties, or scale poorly for a large number of parties. In this paper, we design and implement a new system for highly efficient and scalable...

In CRYPTO 2019, Gohr showed that well-trained neural networks could perform cryptanalytic distinguishing tasks superior to differential distribution table (DDT)-based distinguishers. This suggests that the differential-neural distinguisher (ND) may use additional information besides pure ciphertext differences. However, the explicit knowledge beyond differential distribution is still unclear. In this work, we provide explicit rules that can be used alongside DDTs to enhance the effectiveness...

Sigma protocols are one of the most common and efficient zero-knowledge proofs (ZKPs). Over the decades, a large number of Sigma protocols are proposed, yet few works pay attention to the common design principal. In this work, we propose a generic framework of Sigma protocols for algebraic statements from verifiable secret sharing (VSS) schemes. Our framework provides a general and unified approach to understanding Sigma protocols. It not only neatly explains the classic protocols such as...

Reversed multiplication friendly embedding (RMFE) amortization has been playing an active role in the state-of-the-art constructions of MPC protocols over rings (in particular, the ring $\mathbb{Z}_{2^k}$). As far as we know, this powerful technique has NOT been able to find applications in the crown jewel of two-party computation, the non-interactive secure computation (NISC), where the requirement of the protocol being non-interactive constitutes a formidable technical bottle-neck. We...

The question of whether public-key encryption (PKE) can be constructed from the assumption that one-way functions (OWF) exist remains a central open problem. In this paper we give two constructions of bit PKE scheme derived from any NP language L, along with a polynomial-time instance-witness sampling algorithm. Furthermore, we prove that if L is average hard NP language, the the presented schemes is CPA secure. Our results give a positive answer to this longstanding problem, as the...

Decentralized Finance (DeFi), a blockchain-based financial ecosystem, suffers from smart contract vulnerabilities that led to a loss exceeding 3.24 billion USD by April 2022. To address this, blockchain firms audit DeFi applications, a process known as DeFi auditing. Our research aims to comprehend the mechanism and efficacy of DeFi auditing. We discovered its ability to detect vulnerabilities in smart contract logic and interactivity with other DeFi entities, but also noted its limitations...

The Hidden Number Problem (HNP) has been extensively used in the side-channel attacks against (EC)DSA and Diffie-Hellman. The lattice approach is a primary method of solving the HNP. In EUROCRYPT 2021, Albrecht and Heninger constructed a new lattice to solve the HNP, which converts the HNP to the SVP. After that, their approach became the state-of-the-art lattice method of solving the HNP. But Albrecht and Heninger's approach has a high failure rate for solving the HNP with one bit of nonce...

The celebrated result of Yao (FOCS'82) shows that concatenating $n\cdot p(n)$ copies of a weak one-way function (OWF) $f$, which can be inverted with probability $1-\tfrac{1}{p(n)}$, yields a strong OWF $g$, showing that weak and strong OWFs are black-box equivalent. Yao's transformation is not security-preserving, i.e., the input to $g$ needs to be much larger than the input to $f$. Understanding whether a larger input is inherent is a long-standing open question. In this work, we...

Time-lock puzzles wrap a solution $\mathrm{s}$ inside a puzzle $\mathrm{P}$ in such a way that ``solving'' $\mathrm{P}$ to find $\mathrm{s}$ requires significantly more time than generating the pair $(\mathrm{s},\mathrm{P})$, even if the adversary has access to parallel computing; hence it can be thought of as sending a message $\mathrm{s}$ to the future. It is known [Mahmoody, Moran, Vadhan, Crypto'11] that when the source of hardness is only a random oracle, then any puzzle generator with...

We study the relationship between notions of pseudorandomness in the quantum and classical worlds. Pseudorandom quantum state generator (PRSG), a pseudorandomness notion in the quantum world, is an efficient circuit that produces states that are computationally indistinguishable from Haar random states. PRSGs have found applications in quantum gravity, quantum machine learning, quantum complexity theory, and quantum cryptography. Pseudorandom generators, on the other hand, a pseudorandomness...

An oblivious Top-$k$ algorithm selects the $k$ smallest elements from $d$ elements while ensuring the sequence of operations and memory accesses do not depend on the input. In 1969, Alekseev proposed an oblivious Top-$k$ algorithm with complexity $O(d \log^2{k})$, which was later improved by Yao in 1980 for small $k \ll \sqrt{d}$. In this paper, we revisit the literature on oblivious Top-$k$ and propose another improvement of Alekseev's method that outperforms both for large $k =...

Updatable encryption is a useful primitive that enables key rotation for storing data on an untrusted storage provider without the leaking anything about the plaintext or the key. In this work, we make two contributions. Firstly, we extend updatable encryption to the public-key setting, providing its security model and three different efficient constructions. Using a public-key updatable encryption scheme, a user can receive messages directly in the cloud from multiple senders without...

In a vertical federated learning (VFL) system consisting of a central server and many distributed clients, the training data are vertically partitioned such that different features are privately stored on different clients. The problem of split VFL is to train a model split between the server and the clients. This paper aims to address two major challenges in split VFL: 1) performance degradation due to straggling clients during training; and 2) data and model privacy leakage from clients’...

Commitments are fundamental in cryptography. In the classical world, commitments are equivalent to the existence of one-way functions. It is also known that the most desired form of commitments in terms of their round complexity, i.e., non-interactive commitments, cannot be built from one-way functions in a black-box way [Mahmoody-Pass, Crypto'12]. However, if one allows the parties to use quantum computation and communication, it is known that non-interactive commitments (to classical bits)...

Garbled circuits are a fundamental cryptographic primitive that allows two or more parties to securely evaluate an arbitrary Boolean circuit without revealing any information beyond the output using a constant number of communication rounds. Garbled circuits have been introduced by Yao (FOCS’86) and generalized to the multi-party setting by Beaver, Micali and Rogaway (STOC’90). Since then, several works have improved their efficiency by providing different garbling schemes and several...

A recent line of works on zero-knowledge (ZK) protocols with a vector oblivious linear function evaluation (VOLE)-based offline phase provides a new paradigm for scalable ZK protocols featuring fast proving and small prover memory. Very recently, Baum et al. (Crypto'23) proposed the VOLE-in-the-head technique, allowing such protocols to become publicly verifiable. Many practically efficient protocols for proving circuit satisfiability over any Galois field are implemented, while protocols...

Critical and widely used cryptographic protocols have repeatedly been found to contain flaws in their design and their implementation. A prominent class of such vulnerabilities is logical attacks, e.g. attacks that exploit flawed protocol logic. Automated formal verification methods, based on the Dolev-Yao (DY) attacker, formally define and excel at finding such flaws, but operate only on abstract specification models. Fully automated verification of existing protocol implementations is...

Messaging Layer Security (MLS), currently undergoing standardization at the IETF, is an asynchronous group messaging protocol that aims to be efficient for large dynamic groups, while providing strong guarantees like forward secrecy (FS) and post-compromise security (PCS). While prior work on MLS has extensively studied its group key establishment component (called TreeKEM), many flaws in early designs of MLS have stemmed from its group integrity and authentication mechanisms that are not as...

Updatable encryption (UE) enables a cloud server to update ciphertexts using client-generated tokens. There are two types of UE: ciphertext-independent (c-i) and ciphertext-dependent (c-d). In terms of construction and efficiency, c-i UE utilizes a single token to update all ciphertexts. The update mechanism relies mainly on the homomorphic properties of exponentiation, which limits the efficiency of encryption and updating. Although c-d UE may seem inconvenient as it requires downloading...

Vehicle-to-everything (V2X) communication is the key enabler for emerging intelligent transportation systems. Applications built on top of V2X require both authentication and privacy protection for the vehicles. The common approach to meet both requirements is to use pseudonyms which are short-term identities. However, both industrial standards and state-of-the-art research are not designed for resource-constrained environments. In addition, they make a strong assumption about the security...

In most homomorphic encryption schemes based on the RLWE, the native plaintexts are represented as polynomials in a ring $Z_t[x]/x^N+1$ where $t$ is a plaintext modulus and $x^N+1$ is a cyclotomic polynomial with degree power of two. An encoding scheme should be used to transform some natural data types(such as integers and rational numbers) into polynomials in the ring. After a homomorphic computation on the polynomial is finished, the decoding procedure is invoked to obtain the result....

The Security Protocol and Data Model (SPDM) defines flows to authenticate hardware identity of a computing device. It also allows for establishing a secure session for confidential and integrity protected data communication between two devices. The present version of SPDM, namely version 1.2, relies on traditional asymmetric cryptographic algorithms that are known to be vulnerable to quantum attacks. This paper describes the means by which support for post-quantum (PQ) cryptography can be...

Garbling schemes, invented in the 80's by Yao (FOCS'86), have been a versatile and fundamental tool in modern cryptography. A prominent application of garbled circuits is constant round secure two-party computation, led to a long line of study of this object, where one of the most influential optimizations is Free-XOR (Kolesnikov and Schneider ICALP'08), introducing a global offset $\Delta$ for all garbled wire values where XOR gates are computed locally without garbling them. To date,...

In 1986, A.Yao introduced the notion of garbled circuits, designed to verify the correctness of computations performed on an untrusted server. However, correctness is guaranteed for only one input, meaning that a new garbled circuit must be created for each new input. To address this drawback, in 2010 Gennaro et al. performed the evaluation of the garbled circuit homomorphically using Fully Homomorphic Encryption scheme, allowing to reuse the same garbled circuit for new inputs. Their...

Attribute-based proxy re-encryption (AB-PRE) is one of the essential variants for proxy re-encryption. It allows a proxy with a re-encryption key to transform a ciphertext associated with an access policy and decryptable by a delegator into another ciphertext associated with a new access policy, thereafter other delegatees can decrypt. However, with AB-PRE, the proxy is to switch the underlying policies of all ciphertexts indiscriminately. The delegator cannot decide which ciphertext would...

The understanding of directionality for updatable encryption (UE) schemes is important, but not yet completed in the literature. We show that security in the backward-leak uni-directional key updates setting is equivalent to the no-directional one. Combining with the work of Jiang (ASIACRYPT 2020) and Nishimaki (PKC 2022), it is showed that the backward-leak notion is the strongest one among all known key update notions and more relevant in practice. We propose two novel generic...

A distribution is k-incompressible, Yao [FOCS ’82], if no efficient compression scheme compresses it to less than k bits. While being a natural measure, its relation to other computational analogs of entropy such as pseudoentropy, Hastad, Impagliazzo, Levin, and Luby [SICOMP 99], and to other cryptographic hardness assumptions, was unclear. We advance towards a better understating of this notion, showing that a k-incompressible distribution has (k−2) bits of next-block pseudoentropy, a...

We study the following question, first publicly posed by Hosoyamada and Yamakawa in 2018. Can parties Alice and Bob with quantum computing power and classical communication rely only on a random oracle (that can be queried in quantum superposition) to agree on a key that is private from eavesdroppers? We make the first progress on the question above and prove the following. When only one of the parties is classical and the other party is quantum powered, as long as they ask a total of $d$...

At ITCS 2020, Bartusek et al. proposed a candidate indistinguishability obfuscator (iO) for affine determinant programs (ADPs). The candidate is special since it directly applies specific randomization techniques to the underlying ADP, without relying on the hardness of traditional cryptographic assumptions like discrete-log or learning with errors. It is relatively efficient compared to the rest of the iO candidates. However, the obfuscation scheme requires further cryptanalysis since it...

The SM4 block cipher was first released in 2006 as SMS4 used in the Chinese national standard WAPI, and became a Chinese national standard in 2016 and an ISO international standard in 2021. White-box cryptography aims primarily to protect the secret key used in a cryptographic software implementation in the white-box scenario that assumes an attacker to have full access to the execution environment and execution details of an implementation. Since white-box cryptography has many real-life...

We provide the first isogeny-based group signature (GS) and accountable ring signature (ARS) that are provably secure in the quantum random oracle model (QROM). We do so by building an intermediate primitive called openable sigma protocol and show that every such protocol gives rise to a secure ARS and GS. Additionally, the QROM security is guaranteed if the perfect unique-response property is satisfied. Our design, with the underlying protocol satisfying this essential unique-response...

Fair data trading online is a challenging task when there is mistrust between data providers and data collectors. The trust issue leads to an unsolvable situation where the data collector is unwilling to pay until she receives the data while the data provider will not send the data unless she receives the payment. The traditional solutions toward fair data trading rely on the trust-third party. After the emergence of the blockchain, many researchers use a smart contract on blockchain as a...

Predicting the level and exploitability of side-channel leakage from complex SoC design is a challenging task. We present Saidoyoki, a test platform that enables the assessment of side-channel leakage under two different settings. The first is pre-silicon side-channel leakage estimation in SoC, and it requires the use of fast side-channel leakage estimation from a high level design description. The second is post-silicon side-channel leakage measurement and analysis in SoC, and it requires a...

We revisit one of the most fundamental hardness amplification constructions, originally proposed by Yao (FOCS 1982). We present a hardness amplification theorem for the direct product of certain games that is simpler, more general, and stronger than previously known hardness amplification theorems of the same kind. Our focus is two-fold. First, we aim to provide close-to-optimal concrete bounds, as opposed to asymptotic ones. Second, in the spirit of abstraction and reusability, our goal is...

We introduce the notion of \emph{elementary MPC} reductions that allow us to securely compute a functionality $f$ by making a single call to a constant-degree ``non-cryptographic'' functionality $g$ without requiring any additional interaction. Roughly speaking, ``non-cryptographic'' means that $g$ does not make use of cryptographic primitives, though the parties can locally call such primitives. Classical MPC results yield such elementary reductions in various cases including the setting...

Pairings have been widely used since their introduction to cryptography. They can be applied to identity-based encryption, tripartite Diffie-Hellman key agreement, blockchain and other cryptographic schemes. The Acceleration of pairing computations is crucial for these cryptographic schemes or protocols. In this paper, we will focus on the Elliptic Net algorithm which can compute pairings in polynomial time, but it requires more storage than Miller’s algorithm. We use several methods to...

Mixed Integer Linear Programming (MILP) solvers have become one of the most powerful tools for searching cryptographic characteristics, including differentials, impossible differentials, and division trails. Generally, one MILP problem can be formulated by several different MILP models, and the models with fewer constraints and variables are usually easier to solve. How to model a subset of $Z_2^n$ with the least number of constraints is also an interesting mathematical problem. In this...

Side-channel and fault injection attacks reveal secret information by monitoring or manipulating the physical effects of computations involving secret variables. Circuit-level countermeasures help to deter these attacks, and traditionally such countermeasures have been developed for each attack vector separately. We demonstrate a multipurpose ring oscillator design - Programmable Ring Oscillator (PRO) to address both fault attacks and side-channel attacks in a generic,...

Attribute-based conditional proxy re-encryption (AB-CPRE) allows delegators to carry out attribute-based control on the delegation of decryption by setting policies and attribute vectors. The fine-grained control of AB-CPRE makes it suitable for a variety of applications, such as cloud storage and distributed file systems. However, all existing AB-CPRE schemes are constructed under classical number-theoretic assumptions, which are vulnerable to quantum cryptoanalysis. Therefore, we propose...

Cube attack has recently been proved as the most effective approach of attacking Trivium. So far, the attack against the highest round-reduced Trivium was given in EUROCRYPT 2020, where key-recovery attacks on 840-, 841-, and 842-round Trivium were presented. By revealing the relation between three-subset division property without unknown subset and the monomials of superpolys, Hu et al. obtained more attacks on 840-, 841-, and 842-round Trivium with lower complexities in ASIACRYPT 2020. In...

While side-channel leakage is traditionally evaluated from a fabricated chip, it is more time-efficient and cost-effective to do so during the design phase of the chip. We present Pre-silicon Architecture Correlation Analysis (PACA), a hardware design analysis methodology to help designer locate and mitigate the vulnerabilities in the design at an early design stage. PACA first ranks the individual cells in a design netlist according to their contribution to the ...

We propose a novel MPC framework, Manticore, in the multiparty setting, with full threshold and semi-honest security model, supporting a combination of real number arithmetic (arithmetic shares), Boolean arithmetic (Boolean shares) and garbled circuits (Yao shares). In contrast to prior work [MZ17, MR18], Manticore never overflows, an important feature for machine learning applications. It achieves this without compromising efficiency or security. Compared to other overflow-free...

Power-based side-channel leakage is a known problem in the design of security-centric electronic systems. As the complexity of modern systems rapidly increases through the use of System-on-Chip (SoC) integration, it becomes difficult to determine the precise source of the side-channel leakage. Designers of secure SoC must therefore proactively apply expensive countermeasures to protect entire subsystems such as encryption modules, and this increases the design cost of the chip. We propose a...

CRAFT is a lightweight tweakable block cipher proposed at FSE 2019, which allows countermeasures against Differential Fault Attacks to be integrated into the cipher at the algorithmic level with ease. CRAFT employs a lightweight and involutory S-box and linear layer, such that the encryption function can be turned into decryption at a low cost. Besides, the tweakey schedule algorithm of CRAFT is extremely simple, where four 64-bit round tweakeys are generated and repeatedly used. Due to a...

Lattice-based cryptography, as an active branch of post-quantum cryptography (PQC), has drawn great attention from side-channel analysis researchers in recent years. Despite the various side-channel targets examined in previous studies, detail on revealing the secret-dependent information efficiently is less studied. In this paper, we propose adaptive EM side-channel attacks with carefully constructed ciphertexts on Kyber, which is a finalist of NIST PQC standardization project. We...

It is of folkloric belief that the security of classical cryptographic protocols is automatically broken if the Adversary is allowed to perform superposition queries and the honest players forced to perform actions coherently on quantum states. Another widely held intuition is that enforcing measurements on the exchanged messages is enough to protect protocols from these attacks. However, the reality is much more complex. Security models dealing with superposition attacks only consider...

We study time/memory tradeoffs of function inversion: an algorithm, i.e., an inverter, equipped with an $s$-bit advice on a randomly chosen function $f\colon [n] \mapsto [n]$ and using $q$ oracle queries to $f$, tries to invert a randomly chosen output $y$ of $f$, i.e., to find $x\in f^{-1}(y)$. Much progress was done regarding adaptive function inversion - the inverter is allowed to make adaptive oracle queries. Hellman [IEEE transactions on Information Theory '80] presented an adaptive...

Updatable encryption schemes allow for key rotation on ciphertexts. A client outsourcing storage of encrypted data to a cloud server can change its encryption key. The cloud server can update the stored ciphertexts to the new key using only a token provided by the client. This paper solves two open problems in updatable encryption, that of uni-directional vs. bi-directional updates, and post-quantum security. The main result in this paper is to analyze the security notions based on uni-...

Side-channel leakage detection methods based on statistical tests, such as t-test or chi^2-test, provide high confidence in the presence of leakage with a large number of traces. However, practical limitations on testing time and equipment may set an upper-bound on the number of traces available, turning the number of traces into a limiting factor in side-channel leakage detection. We describe a statistical technique, based on statistical bootstrapping, that significantly improves the...

Protocols for secure multiparty computation (MPC) enable a set of parties to interact and compute a joint function of their private inputs while revealing nothing but the output. The potential applications for MPC are huge: privacy-preserving auctions, private DNA comparisons, private machine learning, threshold cryptography, and more. Due to this, MPC has been an intensive topic of research in academia ever since it was introduced in the 1980s by Yao for the two-party case (FOCS 1986), and...

Recently, in IEEE Internet of Things Journal (DOI: 10.1109/JIOT.2019.2923373 ), Banerjee et al. proposed a lightweight anonymous authenticated key exchange scheme for IoT based on symmetric cryptography. In this paper, we show that the proposal can not resist impersonation attacks due to vulnerable mutual authentication, and give improvements.

Updatable encryption allows a client to outsource ciphertexts to some untrusted server and periodically rotate the encryption key. The server can update ciphertexts from an old key to a new key with the help of an update token, received from the client, which should not reveal anything about keys or plaintexts to an adversary. We provide a new and highly efficient suite of updatable encryption schemes that we collectively call SHINE. In the variant designed for short messages, ciphertext...

In cloud-based outsourced storage systems, many users wish to securely store their files for later retrieval, and additionally to share them with other users. These retrieving users may not be online at the point of the file upload, and in fact they may never come online at all. In this asynchoronous environment, key transport appears to be at odds with any demands for forward secrecy. Recently, Boyd et al. (ISC 2018) presented a protocol that allows an initiator to use a modified key...

A garbling scheme enables one to garble a circuit C and an input x in a way that C(x) can be evaluated, but nothing else is revealed. Since the first construction by Yao, there have been tremendous practical efficiency improvements for selectively secure garbling schemes, where the adversary is forced to choose both input and circuit to be garbled at the same time. However, in the more realistic setting of adaptive security --where an adversary can choose the input adaptively based on the...

The task of function inversion is central to cryptanalysis: breaking block ciphers, forging signatures, and cracking password hashes are all special cases of the function-inversion problem. In 1980, Hellman showed that it is possible to invert a random function $f\colon [N] \to [N]$ in time $T = \widetilde{O}(N^{2/3})$ given only $S = \widetilde{O}(N^{2/3})$ bits of precomputed advice about $f$. Hellman’s algorithm is the basis for the popular “Rainbow Tables” technique (Oechslin, 2003),...

Kerberos is one of the earliest network security protocols, providing authentication between clients and servers with the assistance of trusted servers. It remains widely used, notably as the default authentication protocol in Microsoft Active Directory (thus shipped with every major operating system), and is the ancestor of modern single sign-on protocols like OAuth and OpenID Connect. There have been many analyses of Kerberos in the symbolic (Dolev--Yao) model, which is more amenable to...

Sampling from discrete Gaussian distribution has applications in lattice-based post-quantum cryptography. Several efficient solutions have been proposed in recent years. However, making a Gaussian sampler secure against timing attacks turned out to be a challenging research problem. In this work, we observed an important property of the input random bit strings that generate samples in Knuth-Yao sampling. We delineate a generic step-by-step method to instantiate a discrete Gaussian sampler...

We present new preimage attacks on standard Keccak-224 and Keccak-256 that are reduced to 3 and 4 rounds. An allocating approach is used in the attacks, and the whole complexity is allocated to two stages, such that fewer constraints are considered and the complexity is lowered in each stage. Specifically, we are trying to find a 2-block preimage, instead of a 1-block one, for a given hash value, and the first and second message blocks are found in two stages, respectively. Both the...

Memory-constrained devices, including widely used smart cards, require resisting attacks by the quantum computers. Lattice-based encryption scheme possesses high efficiency and reliability which could run on small devices with limited storage capacity and computation resources such as IoT sensor nodes or smart cards. We present the first implementation of a lattice-based encryption scheme on the standard Java Card platform by combining number theoretic transform and improved Montgomery...

Leakage-resilient encryption is a powerful tool to protect data confidentiality against side channel attacks. In this work, we introduce a new and strong leakage setting to counter backdoor (or Trojan horse) plus covert channel attack, by relaxing the restrictions on leakage. We allow \emph{bounded} leakage at \emph{anytime} and \emph{anywhere} and over \emph{anything}. Our leakage threshold (e.g. 10000 bits) could be much larger than typical secret key (e.g. AES key or RSA private key)...

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 analyze the FOO electronic voting protocol in the provable secu- rity model using the technique of Computationally Complete Symbolic Attacker (CCSA). The protocol uses commitments, blind signatures and anonymous chan- nels to achieve vote privacy. Unlike the Dolev-Yao analyses of the protocol, we assume neither perfect cryptography nor existence of perfectly anonymous chan- nels. Our analysis reveals new attacks on vote privacy, including an attack that arises due to the inadequacy of the...

Aggregate signature (AS) allows non-interactively condensing multiple individual signatures into a compact one. Besides the faster verification, it is useful to reduce storage and bandwidth, and is especially attractive for blockchain and cryptocurrency. In this work, we first demonstrate the subtlety of achieving AS from general groups, by a concrete attack that actually works against the natural implementations of AS based on almost all the variants of DSA and Schnorr’s. Then, we show that...

Machine learning is widely used to produce models for a range of applications and is increasingly offered as a service by major technology companies. However, the required massive data collection raises privacy concerns during both training and prediction stages. In this paper, we design and implement a general framework for privacy-preserving machine learning and use it to obtain new solutions for training linear regression, logistic regression and neural network models. Our protocols are...

We design a group key exchange protocol with forward secrecy where most of the participants remain offline until they wish to compute the key. This is well suited to a cloud storage environment where users are often offline, but have online access to the server which can assist in key exchange. We define and instantiate a new primitive, a blinded KEM, which we show can be used in a natural way as part of our generic protocol construction. Our new protocol has a security proof based on a...

Trusted computing technologies may play a key role for cloud security as they enable users to relax the trustworthiness assumptions about the provider that operates the physical cloud infrastructure. This work focuses on the possibility of embodying Field-Programmable Gate Array (FPGA) devices in cloud-based infrastructures, where they can benefit compute-intensive workloads like data compression, machine learning, data encoding, etc. The focus is on the implications for cloud applications...

In the setting of secure computation, a set of parties wish to compute a joint function of their private inputs without revealing anything but the output. Garbled circuits, first introduced by Yao, are a central tool in the construction of protocols for secure computation (and other tasks like secure outsourced computation), and are the fastest known method for constant-round protocols. In this paper, we initiate a study of garbling multivalent-logic circuits, which are circuits whose wires...

Ridge regression is an algorithm that takes as input a large number of data points and finds the best-fit linear curve through these points. It is a building block for many machine-learning operations. This report presents a system for privacy-preserving ridge regression. The system outputs the best-fit curve in the clear, but exposes no other information about the input data. This problem was elegantly addressed by Nikolaenko et al. (S\&P 2013). They suggest an approach that combines...

For many cryptographic primitives, it is relatively easy to achieve selective security (where the adversary commits a-priori to some of the choices to be made later in the attack) but appears difficult to achieve the more natural notion of adaptive security (where the adversary can make all choices on the go as the attack progresses). A series of several recent works shows how to cleverly achieve adaptive security in several such scenarios including generalized selective decryption...

Machine learning models hosted in a cloud service are increasingly popular but risk privacy: clients sending prediction requests to the service need to disclose potentially sensitive information. In this paper, we explore the problem of privacy-preserving predictions: after each prediction, the server learns nothing about clients' input and clients learn nothing about the model. We present MiniONN, the first approach for transforming an existing neural network to an oblivious neural network...

Identity-based sequential aggregate signature (IBSAS) schemes are usually applied to secure network routing and sensor networks, since they allow multiple signers to sequentially produce a short signature of different messages to reduce bandwidth overhead and storage space for signatures, and allow signers to attest to these messages as well as the order in which they signed using their identities. In CCS’07, Boldyreva et al. introduced this concept and constructed the first IBSAS scheme in...

Since May (Crypto'02) revealed the vulnerability of the small CRT-exponent RSA using Coppersmith's lattice-based method, several papers have studied the problem and two major improvements have been made. (1) Bleichenbacher and May (PKC'06) proposed an attack for small $d_q$ when the prime factor $p$ is significantly smaller than the other prime factor $q$; the attack works for $p<N^{0.468}$. (2) Jochemsz and May (Crypto'07) proposed an attack for small $d_p$ and $d_q$ when the prime factors...

Yao's garbling scheme is one of the basic building blocks of cryptographic protocol design. Originally designed to enable two-message, two-party secure computation, the scheme has been extended in many ways and has innumerable applications. Still, a basic question has remained open throughout the years: Can the scheme be extended to guarantee security in the face of an adversary that corrupts both parties, adaptively, as the computation proceeds? We answer this question in the...

Maximal distance separable (MDS) matrices are important components for block ciphers. In this paper, we present an algorithm for searching $4\times 4$ MDS matrices over GL(4, $\mathbb{F}_2$). By this algorithm, we find all the lightest MDS matrices have only 10 XOR counts. Besides, all these lightest MDS matrices are classified to 3 types, and some necessary and sufficient conditions are presented for them as well. Some theoretical results can be generalized to the case $GL(m,\mathbb{F}_2)$...

Protocols for securely comparing private values are among the most fundamental building blocks of multiparty computation. Introduced by Yao under the name millionaire's problem, they have found numerous applications in a variety of privacy-preserving protocols; however, due to their inherent non-arithmetic structure, existing construction often remain an important bottleneck in large-scale secure protocols. In this work, we introduce new protocols for securely computing the greater-than and...

Kerberos is one of the most important cryptographic protocols, first because it is the basisc authentication protocol in Microsoft's Active Directory and shipped with every major operating system, and second because it served as a model for all Single-Sign-On protocols (e.g. SAML, OpenID, MS Cardspace, OpenID Connect). Its security has been confirmed with several Dolev-Yao style proofs, and attacks on certain versions of the protocol have been described. However despite its importance,...

In 1982, Yao introduced a fundamental technique of ``circuit garbling'' that became a central building block in cryptography. Recently, the question of garbling general random-access memory (RAM) programs received a lot of attention in the literature where garbling an encrypted data can be done separately from garbling program(s) that execute on this (garbled) RAM. The most recent results of Garg, Lu, and Ostrovsky (FOCS 2015) achieve a garbled RAM with black-box use of any one-way functions...

Recently, several new techniques were presented to dramatically improve key parts of secure two-party computation (2PC) protocols that use the cut-and-choose paradigm on garbled circuits for 2PC with security against malicious adversaries. These include techniques for reducing the number of garbled circuits (Lindell 13, Huang et al.~13, Lindell and Riva 14, Huang et al.~14) and techniques for reducing the overheads besides garbled circuits (Mohassel and Riva 13, Shen and Shelat~13). We...

We revisit the question, originally posed by Yao (1982), of whether encryption security may be characterized using computational information. Yao provided an affirmative answer, using a compression-based notion of computational information to give a characterization equivalent to the standard computational notion of semantic security. We give two other equivalent characterizations. The first uses a computational formulation of Kelly's (1957) model for "gambling with inside information",...

Protocols for secure computation enable mutually distrustful parties to jointly compute on their private inputs without revealing anything but the result. Over recent years, secure computation has become practical and considerable effort has been made to make it more and more efficient. A highly important tool in the design of two-party protocols is Yao's garbled circuit construction (Yao 1986), and multiple optimizations on this primitive have led to performance improvements of orders of...

Public-key cryptography based on the ``ring-variant'' of the Learning with Errors (ring-LWE) problem is both efficient and believed to remain secure in a post-quantum world. In this paper, we introduce a carefully-optimized implementation of a ring-LWE encryption scheme for 8-bit AVR processors like the ATxmega128. Our research contributions include several optimizations for the Number Theoretic Transform (NTT) used for polynomial multiplication. More concretely, we describe the Move-and-Add...

In the design of differentially private mechanisms, it’s usually assumed that a uniformly random source is available. However, in many situations it seems unrealistic, and one must deal with various imperfect random sources. Dodis et al. (CRYPTO’12) presented that differential privacy can be achieved with Santha-Vazirani (SV) source via adding a stronger property called SV-consistent sampling and left open question if differential privacy is possible with more realistic (i.e., less...

We reinvestigate a notion of {\em one-time programs} introduced in the CRYPTO 2008 paper by Goldwasser {\it et~al.} A one-time program is a device containing a program $C$, with the property that the program $C$ can be executed on at most one input. Goldwasser {\it et~al.}~show how to implement one-time programs on devices equipped with special hardware gadgets called {\em one-time memory} tokens. We provide an alternative construction that does not rely on the hardware gadgets. ...