Authentication often bridges real-world individuals and their virtual public identities, like usernames, user IDs and e-mails, exposing vulnerabilities that threaten user privacy. This research introduces COCO (Coconuts and Oblivious Computations for Orthogonal Authentication), a framework that segregates roles among Verifiers, Authenticators, and Clients to achieve privacy-preserving authentication. COCO eliminates the need for Authenticators to directly access virtual public identifiers...

The growing adoption of secure multi-party computation (MPC) has driven the development of efficient symmetric key primitives tailored for MPC. Recent advancements, such as the alternating moduli paradigm, have shown promise but leave room for cryptographic and practical improvements. In this paper, we analyze a family of weak pseudorandom functions (wPRF) proposed at Crypto 2024, focusing on the One-to-One parameter sets. We demonstrate that these configurations fail to achieve their...

While in classical cryptography, one-way functions (OWFs) are widely regarded as the “minimal assumption,” the situation in quantum cryptography is less clear. Recent works have put forward two concurrent candidates for the minimal assumption in quantum cryptography: One-way state generators (OWSGs), postulating the existence of a hard search problem with an efficient verification algorithm, and EFI pairs, postulating the existence of a hard distinguishing problem. Two recent papers [Khurana...

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

The problem of reliable/secure all-to-all communication over low-degree networks has been essential for communication-local (CL) n-party MPC (i.e., MPC protocols where every party directly communicates only with a few, typically polylogarithmic in n, parties) and more recently for communication over ad hoc networks, which are used in blockchain protocols. However, a limited number of adaptively secure solutions exist, and they all make relatively strong assumptions on the ability of parties...

We study those $(n,n)$-permutations, and more generally those balanced $(n,m)$-functions, whose component functions all admit a derivative equal to constant function 1 (this property itself implies balancedness). We call these functions quadratic-like permutations (resp. quadratic-like balanced functions) since all quadratic balanced functions have this property. We show that all Feistel permutations, all crooked permutations and (more generally) all balanced strongly plateaued functions...

Among the various threats to secure ICs, many are semi-invasive in the sense that their application requires the removal of the package to gain access to either the front or back of the target IC. Despite this stringent application requirements, little attention is paid to embedded techniques aiming at checking the package's integrity. This paper explores the feasibility of verifying the package integrity of microcontrollers by examining their thermal dissipation capability.

Achieving malicious security with high efficiency in dishonest-majority secure multiparty computation is a formidable challenge. The milestone works SPDZ and TinyOT have spawn a large family of protocols in this direction. For boolean circuits, state-of-the-art works (Cascudo et. al, TCC 2020 and Escudero et. al, CRYPTO 2022) have proposed schemes based on reverse multiplication-friendly embedding (RMFE) to reduce the amortized cost. However, these protocols are theoretically described and...

Private Set Intersection (PSI) enables a sender and a receiver to jointly compute the intersection of their sets without disclosing non-trivial information about other items. However, depending on the context of joint data analysis, information derived from the items in the intersection may also be considered sensitive. To protect such sensitive information, prior work proposed Differentially private PSI (DPSI), which can be instantiated with circuit-PSI using Fully Homomorphic Encryption....

There has been significant progress over the past seven years in model reverse engineering (RE) for neural network (NN) hardware. Although there has been systematization of knowledge (SoK) in an overall sense, however, the treatment from the hardware perspective has been far from adequate. To bridge this gap, this paper systematically categorizes the types of NN hardware used prevalently by the industry/academia, and also the model RE attacks/defenses published in each category. Further, we...

Recent years have exhibited an increase in applications that distribute trust across $n$ servers to protect user data from a central point of attack. However, these deployments remain limited due to a core obstacle: establishing $n$ distinct trust domains. An application provider, a single trust domain, cannot directly deploy multiple trust domains. As a result, application providers forge business relationships to enlist third-parties as trust domains, which is a manual, lengthy, and...

We present the first comprehensive approach for detecting and analyzing symmetric cryptographic primitives in gate-level descriptions of hardware. To capture both ASICs and FPGAs, we model the hardware as a directed graph, where gates become nodes and wires become edges. For modern chips, those graphs can easily consist of hundreds of thousands of nodes. More abstractly, we find subgraphs corresponding to cryptographic primitives in a potentially huge graph, the sea-of-gates, describing an...

We prove that the permutation computed by a reversible circuit with $\widetilde{O}(nk\cdot \log(1/\epsilon))$ random $3$-bit gates is $\epsilon$-approximately $k$-wise independent. Our bound improves on currently known bounds in the regime when the approximation error $\epsilon$ is not too small. We obtain our results by analyzing the log-Sobolev constants of appropriate Markov chains rather than their spectral gaps.

We revisit the question of the overhead to achieve full security (i.e., guaranteed output delivery) in secure multiparty computation (MPC). Recent works have closed the gap between full security and semi-honest security, by introducing protocols where the parties first compute the circuit using a semi-honest protocol and then run a verification step with sublinear communication in the circuit size. However, in these works the number of interaction rounds in the verification step is also...

This work models a secure integrated sensing and communication (ISAC) system as a wiretap channel with action-dependent channel states and channel output feedback, e.g., obtained through reflections. The transmitted message is split into a common and a secure message, both of which must be reliably recovered at the legitimate receiver, while the secure message needs to be kept secret from the eavesdropper. The transmitter actions, such as beamforming vector design, affect the corresponding...

Consider the task of secure multiparty computation (MPC) among $n$ parties with perfect security and guaranteed output delivery, supporting $t<n/3$ active corruptions. Suppose the arithmetic circuit $C$ to be computed is defined over a finite ring $\mathbb{Z}/q\mathbb{Z}$, for an arbitrary $q\in\mathbb{Z}$. It is known that this type of MPC over such ring is possible, with communication that scales as $O(n|C|)$, assuming that $q$ scales as $\Omega(n)$. However, for constant-size rings...

The (parallel) classical black pebbling game is a helpful abstraction which allows us to analyze the resources (time, space, space-time, cumulative space) necessary to evaluate a function $f$ with a static data-dependency graph $G$ on a (parallel) computer. In particular, the parallel black pebbling game has been used as a tool to quantify the (in)security of Data-Independent Memory-Hard Functions (iMHFs). However, the classical black pebbling game is not suitable to analyze the cost of...

The remarkable performance capabilities of AI accelerators offer promising opportunities for accelerating cryptographic algorithms, particularly in the context of lattice-based cryptography. However, current approaches to leveraging AI accelerators often remain at a rudimentary level of implementation, overlooking the intricate internal mechanisms of these devices. Consequently, a significant number of computational resources is underutilized. In this paper, we present a comprehensive...

Software obfuscation is a powerful tool to protect the intellectual property or secret keys inside programs. Strong software obfuscation is crucial in the context of untrusted execution environments (e.g., subject to malware infection) or to face potentially malicious users trying to reverse-engineer a sensitive program. Unfortunately, the state-of-the-art of pure software-based obfuscation (including white-box cryptography) is either insecure or infeasible in practice. This work...

We explore the possibility of obtaining general-purpose obfuscation for all circuits by way of making only simple, local, functionality preserving random perturbations in the circuit structure. Towards this goal, we use the additional structure provided by reversible circuits, but no additional algebraic structure. We start by formulating a new (and relatively weak) obfuscation task regarding the ability to obfuscate random circuits of bounded length. We call such obfuscators random...

While many modern cryptographic primitives have stood the test of time, attacker have already begun to expand their attacks beyond classical cryptanalysis by specifically targeting implementations. One of the most well-documented classes of such attacks are subversion (or substitution) attacks, where the attacker replaces the Implementation of the cryptographic primitive in an undetectable way such that the subverted implementation leaks sensitive information of the user during a protocol...

We introduce the notion of traceable mixnets. In a traditional mixnet, multiple mix-servers jointly permute and decrypt a list of ciphertexts to produce a list of plaintexts, along with a proof of correctness, such that the association between individual ciphertexts and plaintexts remains completely hidden. However, in many applications, the privacy-utility tradeoff requires answering some specific queries about this association, without revealing any information beyond the query result. We...

Remote side-channel attacks on processors exploit hardware and micro-architectural effects observable from software measurements. So far, the analysis of micro-architectural leakages over physical side-channels (power consumption, electromagnetic field) received little treatment. In this paper, we argue that those attacks are a serious threat, especially against systems such as smartphones and Internet-of-Things (IoT) devices which are physically exposed to the end-user. Namely, we show that...

Password-Authenticated Key Exchange (PAKE) allows two parties to establish a common high-entropy secret from a possibly low-entropy pre-shared secret such as a password. In this work, we provide the first PAKE protocol with subversion resilience in the framework of universal composability (UC), where the latter roughly means that UC security still holds even if one of the two parties is malicious and the honest party's code has been subverted (in an undetectable manner). We achieve this...

We present a general framework for polynomial-time lattice Gaussian sampling. It revolves around a systematic study of the discrete Gaussian measure and its samplers under extensions of lattices; we first show that given lattices $\Lambda'\subset \Lambda$ we can sample efficiently in $\Lambda$ if we know how to do so in $\Lambda'$ and the quotient $\Lambda/\Lambda'$, \emph{regardless} of the primitivity of $\Lambda'$. As a direct application, we...

We provide two improvements to Regev's quantum factoring algorithm (arXiv:2308.06572), addressing its space efficiency and its noise-tolerance. Our first contribution is to improve the quantum space efficiency of Regev's algorithm while keeping the circuit size the same. Our main result constructs a quantum factoring circuit using $O(n \log n)$ qubits and $O(n^{3/2} \log n)$ gates. We achieve the best of Shor and Regev (upto a logarithmic factor in the space complexity): on the one...

Quantum computers hold the potential to solve problems that are intractable for classical computers, thereby driving increased interest in the development of new cryptanalytic ciphers. In NIST's post-quantum standardization process, the security categories are defined by the costs of quantum key search against AES. However, the cost estimates provided by Grassl et al. for the search are high. NIST has acknowledged that these initial classifications should be approached cautiously, since the...

We introduce a novel side-channel-based reverse engineering technique capable of reconstructing a procedure solely from inputs, outputs, and traces of execution. Beyond generic restrictions, we do not assume any prior knowledge of the procedure or the chip it operates on. These restrictions confine our analysis to 8-bit RISC constant-time software implementations. Specifically, we demonstrate the feasibility of reconstructing a symmetric cryptographic cipher, even in scenarios where...

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 open-source hardware IP model has recently started gaining popularity in the developer community. This model offers the integrated circuit (IC) developers wider standardization, faster time-to-market and richer platform for research. In addition, open-source hardware conforms to the Kerckhoff’s principle of a publicly-known algorithm and thus helps to enhance security. However, when security comes into consideration, source transparency is only one part of the solution. A complex global...

In this work, we set out to create a subversion resilient authenticated key exchange protocol. The first step was to design a meaningful security model for this primitive, and our goal was to avoid using building blocks like reverse firewalls and public watchdogs. We wanted to exclude these kinds of tools because we desired that our protocols to be self contained in the sense that we could prove security without relying on some outside, tamper-proof party. To define the model, we began by...

Millions of smart contracts have been deployed onto Ethereum for providing various services, whose functions can be invoked. For this purpose, the caller needs to know the function signature of a callee, which includes its function id and parameter types. Such signatures are critical to many applications focusing on smart contracts, e.g., reverse engineering, fuzzing, attack detection, and profiling. Unfortunately, it is challenging to recover the function signatures from contract bytecode,...

The magic of Fully Homomorphic Encryption (FHE) is that it allows operations on encrypted data without decryption. Unfortunately, the slow computation time limits their adoption. The slow computation time results from the vast memory requirements (64Kbits per ciphertext), a bootstrapping key of 1.3 GB, and sizeable computational overhead (10240 NTTs, each NTT requiring 5120 32-bit multiplications). We accelerate the FHEW bootstrapping in hardware on a high-end U280 FPGA. To reduce the...

Spiking neural networks gain attention due to low power properties and event-based operation, making them suitable for usage in resource constrained embedded devices. Such edge devices allow physical access opening the door for side-channel analysis. In this work, we reverse engineer the parameters of a feed-forward spiking neural network implementation with correlation power analysis. Localized measurements of electro-magnetic emanations enable our attack, despite inherent parallelism and...

One approach for scaling blockchains is to create bilateral, offchain channels, known as payment/state channels, that can protect parties against cheating via onchain collateralization. While such channels have been studied extensively, not much attention has been given to programmability, where the parties can agree to dynamically enforce arbitrary conditions over their payments without going onchain. We introduce the notion of a programmable payment channel ($\mathsf{PPC}$) that allows...

Liquidations in DeFi are both a blessing and a curse — whereas liquidations prevent lenders from capital loss, they simultaneously lead to liquidation spirals and system-wide failures. Since most lending and borrowing protocols assume liquidations are indispensable, there is an increased interest in alternative constructions that prevent immediate systemic-failure under uncertain circumstances. In this work, we introduce reversible call options, a novel financial primitive that enables...

In the recent work of (Cheon & Lee, Eurocrypt'22), the concept of a degree-$D$ packing method was formally introduced, which captures the idea of embedding multiple elements of a smaller ring into a larger ring, so that element-wise multiplication in the former is somewhat "compatible" with the product in the latter. Then, several optimal bounds and results are presented, and furthermore, the concept is generalized from one multiplication to degrees larger than two. These packing...

This work researches the implementation of the AES family with Pauli-X gates, CNOT gates and Toffoli gates as the underlying quantum logic gate set. First, the properties of quantum circuits are investigated, as well as the influence of Pauli-X gates, CNOT gates and Toffoli gates on the performance of the circuits constructed with those gates. Based on these properties and the observations on the hardware circuits built by Boyar \emph{et al.} and Zou \emph{et al.}, it is possible to...

Recently, Chen et al. (ASIACRYPT 2021) introduced a notion called hierarchical integrated signature and encryption (HISE), which provides a new principle for combining public key schemes. It uses a single public key for both signature and encryption schemes, and one can derive a decryption key from the signing key but not vice versa. Whereas, they left the dual notion where the signing key can be derived from the decryption key as an open problem. In this paper, we resolve the problem by...

We conduct a security analysis of the e-voting protocol used for the largest political election using e-voting in the world, the 2022 French legislative election for the citizens overseas. Due to a lack of system and threat model specifications, we built and contributed such specifications by studying the French legal framework and by reverse-engineering the code base accessible to the voters. Our analysis reveals that this protocol is affected by two design-level and implementation-level...

Numerous security vulnerability assessment techniques urge precise and fast finite state machines (FSMs) extraction from the design under evaluation. Sequential logic locking, watermark insertion, fault-injection assessment of a System-ona- Chip (SoC) control flow, information leakage assessment, and reverse engineering at gate-level abstraction, to name a few, require precise FSM extraction from the synthesized netlist of the design. Unfortunately, no reliable solutions are currently...

In the setting of subversion, an adversary tampers with the machines of the honest parties thus leaking the honest parties' secrets through the protocol transcript. The work of Mironov and Stephens-Davidowitz (EUROCRYPT’15) introduced the idea of reverse firewalls (RF) to protect against tampering of honest parties' machines. All known constructions in the RF framework rely on the malleability of the underlying operations in order for the RF to rerandomize/sanitize the transcript. RFs are...

The classical (parallel) black pebbling game is a useful abstraction which allows us to analyze the resources (space, space-time, cumulative space) necessary to evaluate a function $f$ with a static data-dependency graph $G$. Of particular interest in the field of cryptography are data-independent memory-hard functions $f_{G,H}$ which are defined by a directed acyclic graph (DAG) $G$ and a cryptographic hash function $H$. The pebbling complexity of the graph $G$ characterizes the amortized...

At the early stage of the design process, many security vulnerability assessment solutions require fast and precise extraction of the finite state machines (FSMs) present in the register-transfer level (RTL) description of the design. FSMs should be accurately extracted for watermark insertion, fault injection assessment of control paths in a system-on-chip (SoC), information leakage assessment, control-flow reverse engineering in RTL abstraction, logic obfuscation, etc. However, it is quite...

There are many recent results on reverse-engineering (potentially hidden) structure in cryptographic S-boxes. The problem of recovering structure in the other main building block of symmetric cryptographic primitives, namely, the linear layer, has not been paid that much attention so far. To fill this gap, in this work, we develop a systematic approach to decomposing structure in the linear layer of a substitution-permutation network (SPN), covering the case in which the specification of the...

This work considers the problem of mitigating information leakage between communication and sensing in systems jointly performing both operations. Specifically, a discrete memoryless state-dependent broadcast channel model is studied in which (i) the presence of feedback enables a transmitter to convey information, while simultaneously performing channel state estimation; (ii) one of the receivers is treated as an eavesdropper whose state should be estimated but which should remain oblivious...

Interactive oracle proofs (IOPs) are a generalization of probabilistically checkable proofs that can be used to construct succinct arguments. Improvements in the efficiency of IOPs lead to improvements in the efficiency of succinct arguments. Key efficiency goals include achieving provers that run in linear time and verifiers that run in sublinear time, where the time complexity is with respect to the arithmetic complexity of proved computations over a finite field $\mathbb{F}$. We...

Can we hope to provide provable security against model extraction attacks? As a step towards a theoretical study of this question, we unify and abstract a wide range of "observational" model extraction defenses (OMEDs) --- roughly, those that attempt to detect model extraction by analyzing the distribution over the adversary's queries. To accompany the abstract OMED, we define the notion of complete OMEDs --- when benign clients can freely interact with the model --- and sound OMEDs --- when...

In this paper it is shown that PSPACE is equal to 4th level in the polynomial hierarchy. A lot of important consequences are also deduced. True quantified Boolean formula is indeed a generalisation of the Boolean Satisfiability Problem, where determining of interpretation that satisfies a given Boolean formula is replaced by existence of Boolean functions that makes a given QBF to be tautology. Such functions are called the Skolem functions. The essential idea is to skolemize, and...

An integrated circuit is subject to a number of attacks including information leakage, side-channel attacks, fault-injection, malicious change, reverse engineering, and piracy. Majority of these attacks take advantage of physical placement and routing of cells and interconnects. Several measures have already been proposed to deal with security issues of the high level functional design and logic synthesis. However, to ensure end-to-end trustworthy IC design flow, it is necessary to have...

Contact discovery allows users of mobile messengers to conveniently connect with people in their address book. In this work, we demonstrate that severe privacy issues exist in currently deployed contact discovery methods and propose suitable mitigations. Our study of three popular messengers (WhatsApp, Signal, and Telegram) shows that large-scale crawling attacks are (still) possible. Using an accurate database of mobile phone number prefixes and very few resources, we queried 10% of US...

In this work we present a novel actively secure multiparty computation protocol in the dishonest majority setting, where the computation domain is a ring of the type $\mathbb{Z}_{2^k}$. Instead of considering an "extension ring" of the form $\mathbb{Z}_{2^{k+\kappa}}$ as in SPD$\mathbb{Z}_{2^k}$ (Cramer et al, CRYPTO 2018) and its derivatives, we make use of an actual ring extension, or more precisely, a Galois ring extension $\mathbb{Z}_{p^k}[\mathtt{X}]/(h(\mathtt{X}))$ of large enough...

Fully homomorphic encryption~(FHE) has flourished since it was first constructed by Gentry~(STOC 2009). Single instruction multiple data~(SIMD) gave rise to efficient homomorphic operations on vectors in \((\mathbb{F}_{t^d})^\ell\), for prime \(t\). RLWE instantiated with cyclotomic polynomials of the form \(X^{2^N}+1\) dominate implementations of FHE due to highly efficient fast Fourier transformations. However, this choice yields very short SIMD plaintext vectors and high degree extension...

Private set operations allow two parties to perform secure computation on their private sets, including intersection, union and functions of intersection/union. In this paper, we put forth a framework to perform private set operations. The technical core of our framework is the multi-query reverse private membership test (mqRPMT) protocol (Zhang et al., USENIX Security 2023), in which a client with a vector $X = (x_1, \dots, x_n)$ interacts with a server holding a set $Y$, and eventually the...

MPC-in-the-head based zero-knowledge proofs allow one to prove knowledge of a preimage for a circuit defined over a finite field F. In recent proofs the soundness depends on the size F, and small fields require more parallel repetitions, and therefore produce larger proofs. In this paper we develop and systematically apply lifting strategies to such proof protocols in order to increase soundness and reduce proof size. The strategies are (i) lifting parts of the protocol to extension fields...

Hashed Time-Locked Contracts (HTLCs) are a widely used primitive in blockchain systems such as payment channels, atomic swaps, etc. Unfortunately, HTLC is incentive-incompatible and is vulnerable to bribery attacks. The state-of-the-art solution is MAD-HTLC (Oakland'21), which proposes an elegant idea that leverages miners' profit-driven nature to defeat bribery attacks. In this paper, we show that MAD-HTLC is still vulnerable as it only considers a somewhat narrow set of passive...

Structured random strings (SRSs) and correlated randomness are important for many cryptographic protocols. In settings where interaction is expensive, it is desirable to obtain such randomness in as few rounds of communication as possible; ideally, simply by exchanging one reusable round of messages which can be considered public keys. In this paper, we describe how to generate any SRS or correlated randomness in such a single round of communication, using, among other things,...

Private set union (PSU) protocol enables two parties, each holding a set, to compute the union of their sets without revealing anything else to either party. So far, there are two known approaches for constructing PSU protocols. The first mainly depends on additively homomorphic encryption (AHE), which is generally inefficient since it needs to perform a non-constant number of homomorphic computations on each item. The second is mainly based on oblivious transfer and symmetric-key...

Hardware obfuscation through redundancy addition is a well-known countermeasure against reverse engineering. For FPGA designs, such a technique can be implemented with a small overhead, however, its effectiveness is heavily dependent on the stealthiness of the redundant elements. Hardware opaque predicates can provide adequately stealthy constant values that can be used for obfuscation. However, in this report, we show that such obfuscation schemes can be defeated by ensuring the full...

Logic locking is a design concealment mechanism for protecting the IPs integrated into modern System-on-Chip (SoC) architectures from a wide range of hardware security threats at the IC manufacturing supply chain. Logic locking primarily helps the designer to protect the IPs against reverse engineering, IP piracy, overproduction, and unauthorized activation. For more than a decade, the research studies that carried out on this paradigm has been immense, in which the applicability,...

Subversion attacks undermine security of cryptographic protocols by replacing a legitimate honest party's implementation with one that leaks information in an undetectable manner. An important limitation of all currently known techniques for designing cryptographic protocols with security against subversion attacks is that they do not automatically guarantee security in the realistic setting where a protocol session may run concurrently with other protocols. We remedy this situation by...

This work considers the problem of mitigating information leakage between communication and sensing in systems jointly performing both operations. Specifically, a discrete memoryless state-dependent broadcast channel model is studied in which (i) the presence of feedback enables a transmitter to convey information, while simultaneously performing channel state estimation; (ii) one of the receivers is treated as an eavesdropper whose state should be estimated but which should remain...

ARM-based Android smartphones rely on the TrustZone hardware support for a Trusted Execution Environment (TEE) to implement security-sensitive functions. The TEE runs a separate, isolated, TrustZone Operating System (TZOS), in parallel to Android. The implementation of the cryptographic functions within the TZOS is left to the device vendors, who create proprietary undocumented designs. In this work, we expose the cryptographic design and implementation of Android's Hardware-Backed...

Smart contracts are a new form of software that will revolutionize how software is written, IT systems are maintained, and applications and whole businesses are built. Smart contracts are composable and autonomous pieces of software that run on decentralized blockchains, which makes them tamperproof and unstoppable. In this paper, we describe the Internet Computer (IC), which is a radical new design of blockchain that unleashes the full potential of smart contracts, overcoming the...

In this work, we present cost analysis for mounting Grover's key search on Present block cipher. Reversible quantum circuits for Present are designed taking into consideration several decompositions of toffoli gate. This designs are then used to produce Grover oracle for Present and their implementations cost is compared using several metrics. Resource estimation for Grover's search is conducted by employing these Grover oracles. Finally, gate cost for these designs are estimated considering...

Encryption satisfying CCA2 security is commonly known to be unnecessarily strong for realizing secure channels. Moreover, CCA2 constructions in the standard model are far from being competitive practical alternatives to constructions via random oracle. A promising research area to alleviate this problem are weaker security notions—like IND-RCCA secure encryption or IND-atag-wCCA secure tag-based encryption—which are still able to facilitate secure message transfer (SMT) via authenticated...

$\newcommand{\Z}{\mathbb{Z}} \newcommand{\basis}{B}$We study the computational problem of finding a shortest non-zero vector in a rotation of $\Z^n$, which we call $\Z$SVP. It has been a long-standing open problem to determine if a polynomial-time algorithm for $\Z$SVP exists, and there is by now a beautiful line of work showing how to solve it efficiently in certain very special cases. However, despite all of this work, the fastest known algorithm that is proven to solve $\Z$SVP is still...

Intellectual Property (IP) thefts of trained machine learning (ML) models through side-channel attacks on inference engines are becoming a major threat. Indeed, several recent works have shown reverse engineering of the model internals using such attacks, but the research on building defenses is largely unexplored. There is a critical need to efficiently and securely transform those defenses from cryptography such as masking to ML frameworks. Existing works, however, revealed that a...

The discipline of reverse engineering integrated circuits (ICs) is as old as the technology itself. It grew out of the need to analyze competitor’s products and detect possible IP infringements. In recent years, the growing hardware Trojan threat motivated a fresh research interest in the topic. The process of IC reverse engineering comprises two steps: netlist extraction and specification discovery. While the process of netlist extraction is rather well understood and established techniques...

Over the last decade attacks have repetitively demonstrated that bitstream protection for SRAM-based FPGAs is a persistent problem without a satisfying solution in practice. Hence, real-world hardware designs are prone to intellectual property infringement and malicious manipulation as they are not adequately protected against reverse-engineering. In this work, we first review state-of-the-art solutions from industry and academia and demonstrate their ineffectiveness with respect to...

We study Multi-party computation (MPC) in the setting of subversion, where the adversary tampers with the machines of honest parties. Our goal is to construct actively secure MPC protocols where parties are corrupted adaptively by an adversary (as in the standard adaptive security setting), and in addition, honest parties' machines are compromised. The idea of reverse firewalls (RF) was introduced at EUROCRYPT'15 by Mironov and Stephens-Davidowitz as an approach to protecting protocols...

Public knowledge about the structure of a cryptographic system is a standard assumption in the literature and algorithms are expected to guarantee security in a setting where only the encryption key is kept secret. Nevertheless, undisclosed proprietary cryptographic algorithms still find widespread use in applications both in the civil and military domains. Even though side-channel-based reverse engineering attacks that recover the hidden components of custom cryptosystems have been...

We formally define polynomial packing methods and initiate a unified study of related concepts in various contexts of cryptography. This includes homomorphic encryption (HE) packing and reverse multiplication-friendly embedding (RMFE) in information-theoretically secure multi-party computation (MPC). We prove several upper bounds and impossibility results on packing methods for $\mathbb{Z}_{p^k}$ or $\mathbb{F}_{p^k}$-messages into $\mathbb{Z}_{p^t}[x]/f(x)$ in terms of (i) packing density,...

Apple's file-sharing service AirDrop leaks phone numbers and email addresses by exchanging vulnerable hash values of the user's own contact identifiers during the authentication handshake with nearby devices. In a paper presented at USENIX Security'21, we theoretically describe two attacks to exploit these vulnerabilities and propose "PrivateDrop" as a privacy-preserving drop-in replacement for Apple's AirDrop protocol based on private set intersection. In this demo, we show how these...

Micro-architectural leakage is a reality even on low- to midrange commercial processors. Dealing with it is expensive, because micro-architectural leakage is often only discovered after implementation choices have been made (i.e. when evaluating the concrete implementation). We demonstrate that it is feasible, using a recent leakage modelling technique, to reverse engineer significant elements of the micro-architectural leakage of a mid-range commercial processor in a “grey-box” setting. Our...

In recent years machine learning has become increasingly mainstream across industries. Additionally, Graphical Processing Unit (GPU) accelerators are widely deployed in various neural network (NN) applications, including image recognition for autonomous vehicles and natural language processing, among others. Since training a powerful network requires expensive data collection and computing power, its design and parameters are often considered a secret intellectual property of their...

The framework of interactive oracle proofs (IOP) has been used with great success to construct a number of efficient transparent zk-SNARKs in recent years. However, these constructions are based on Reed-Solomon codes and can only be applied directly to statements given in the form of arithmetic circuits or R1CS over large fields $\mathbb{F}$ since their soundness error is at least $1/|\mathbb{F}|$. This motivates the question of what is the best way to apply these IOPs to statements that...

Secure hash functions are widely used in cryptographic algorithms to secure against diverse attacks. A one-way secure hash function is used in the various research fields to secure, for instance, blockchain. Notably, most of the hash functions provide security based on static parameters and publicly known operations. Consequently, it becomes easier to attack by the attackers because all parameters and operations are predefined. The publicly known parameters and predefined operations make the...

The SM4 block cipher is a Chinese domestic crpytographic that was introduced in 2003. Since the algorithm was developed for the use in wireless sensor networks, it is mandated in the Chinese National Standard for Wireless LAN WAPI (Wired Authentication and Privacy Infrastructure). The SM4 block cipher uses a 128-bit block size and a 32-bit round key. This consists of 32 rounds and one reverse translation \texttt{R}. In this paper, we present the optimized implementation of the SM4 block...

It is a well-known fact that the power consumption during certain stages of a cryptographic algorithm exhibits a strong correlation with the Hamming Weight of its underlying variables. This phenomenon has been widely exploited in the cryptographic literature in various attacks targeting a broad range of schemes such as block ciphers or public-key cryptosystems. A common way of breaking this correlation is through the inclusion of countermeasures involving additional randomness into the...

Apple's offline file-sharing service AirDrop is integrated into more than 1.5 billion end-user devices worldwide. We discovered two design flaws in the underlying protocol that allow attackers to learn the phone numbers and email addresses of both sender and receiver devices. As a remediation, we study the applicability of private set intersection (PSI) to mutual authentication, which is similar to contact discovery in mobile messengers. We propose a novel optimized PSI-based protocol called...

This paper proposes the first cache timing side-channel attack on one of Apple’s mobile devices. Utilizing a recent, permanent exploit named checkm8, we reverse-engineered Apple’s BootROM and created a powerful toolkit for running arbitrary hardware security experiments on Apple’s in-house designed ARM systems-on-a-chip (SoC). Using this toolkit, we then implement an access-driven cache timing attack (in the style of PRIME+PROBE) as a proof-of-concept illustrator. The advanced hardware...

In the current crypto paradigm a single secret key transforms a plaintext into a ciphertext and vice versa, or at most a different key is doing the reverse action. Attackers exposed to the ciphertext are hammering it to extract that single key and the plaintext. This paradigm may be challenged with an alternate setup: using a particular crypto algorithm, there is an infinite number of keys that are perfectly interchangeable -- each has the same effect. Nonetheless they are hard to find. And...

Design-hiding techniques are a central piece of academic and industrial efforts to protect electronic circuits from being reverse-engineered. However, these techniques have lacked a principled foundation to guide their design and security evaluation, leading to a long line of broken schemes. In this paper, we begin to lay this missing foundation. We establish formal syntax for design-hiding (DH) schemes, a cryptographic primitive that encompasses all known design-stage methods to hide the...

In proof-of-stake (PoS) blockchains, stakeholders that extend the chain are selected according to the amount of stake they own. In S\&P 2019 the ``Ouroboros Crypsinous'' system of Kerber et al.\ (and concurrently Ganesh et al.\ in EUROCRYPT 2019) presented a mechanism that hides the identity of the stakeholder when adding blocks, hence preserving anonymity of stakeholders both during payment and mining in the Ouroboros blockchain. They focus on anonymizing the messages of the...

For security token adoption by financial institutions and industry players on the blockchain, there is a need for a secure asset management protocol that enables condential asset issuance and transfers by concealing from the public the transfer amounts and asset types, while on a public blockchain. Flexibly supporting arbitrary restrictions on financial transactions, only some of which need to be supported by zero-knowledge proofs. This paper proposes leveraging a hybrid design approach, by...

In this paper, we present a detailed study of the cost of the quantum key search attack using Grover. We consider the popular Feedback Shift Register (FSR) based ciphers Grain-128-AEAD, TinyJAMBU, LIZARD, and Grain-v1 considering the NIST's MAXDEPTH depth restriction. We design reversible quantum circuits for these ciphers and also provide the QISKIT implementations for estimating gate counts. Our results show that cryptanalysis is possible with gate count less than $2^{170}$. In this...

We present the first complete implementation of the offline Simon's algorithm, and estimate its cost to attack the MAC Chaskey, the block cipher PRINCE and the NIST lightweight candidate AEAD scheme Elephant. These attacks require a reasonable amount of qubits, comparable to the number of qubits required to break RSA-2048. They are faster than other collision algorithms, and the attacks against PRINCE and Chaskey are the most efficient known to date. As Elephant has a key smaller than its...

This paper analyzes and optimizes quantum circuits for computing discrete logarithms on binary elliptic curves, including reversible circuits for fixed-base-point scalar multiplication and the full stack of relevant subroutines. The main optimization target is the size of the quantum computer, i.e., the number of logical qubits required, as this appears to be the main obstacle to implementing Shor's polynomial-time discrete-logarithm algorithm. The secondary optimization target is the...

For safe resource management - an effective mechanism/system is necessary that identifies a person and his rights to these resources, using an appropriate key, and its degree of security determines not only the property, but sometimes even the life of its owner. For several decades, it has been based on the security of (bio)material keys, which only guarantee their own authenticity, but not their owner, due to weak of static password protection. In the article will be presented the i-Chip an...

Authenticated dictionaries (ADs) are a key building block of many cryptographic systems, such as transparency logs, distributed &#64257;le systems and cryptocurrencies. In this paper, we propose a new notion of cross-incremental proof (dis)aggregation for authenticated dictionaries, which enables aggregating multiple proofs with respect to different dictionaries into a single, succinct proof. Importantly, this aggregation can be done incrementally and can be later reversed via...

Contact discovery allows users of mobile messengers to conveniently connect with people in their address book. In this work, we demonstrate that severe privacy issues exist in currently deployed contact discovery methods. Our study of three popular mobile messengers (WhatsApp, Signal, and Telegram) shows that, contrary to expectations, large-scale crawling attacks are (still) possible. Using an accurate database of mobile phone number prefixes and very few resources, we have queried 10% of...

At CRYPTO 2018, Cascudo et al. introduced Reverse Multiplication Friendly Embeddings (RMFEs). These are a mechanism to compute $\delta$ parallel evaluations of the same arithmetic circuit over a field $\mathbb{F}_q$ at the cost of a single evaluation of that circuit in $\mathbb{F}_{q^d}$, where $\delta < d$. Due to this inequality, RMFEs are a useful tool when protocols require to work over $\mathbb{F}_{q^d}$ but one is only interested in computing over $\mathbb{F}_q$. In this work we...

In recent years, deep neural networks (DNN) have become an important type of intellectual property due to their high performance on various classification tasks. As a result, DNN stealing attacks have emerged. Many attack surfaces have been exploited, among which cache timing side-channel attacks are hugely problematic because they do not need physical probing or direct interaction with the victim to estimate the DNN model. However, existing cache-side-channel-based DNN reverse engineering...

Simon's algorithm is the first example of a quantum algorithm exponentially faster than any classical algorithm, and has many applications in cryptanalysis. While these quantum attacks are often extremely efficient, they are generally missing some precise cost estimate. This article aims at resolving this issue by computing precise query costs for the different use cases of Simon's algorithm in cryptanalysis. We propose an extensive analysis of Simon's algorithm, and we show that it...

Reverse Firewalls (RFs) were introduced by Mironov and Stephens-Davidowitz to address algorithm-substitution attacks (ASAs) in which an adversary subverts the implementation of a provably-secure cryptographic primitive to make it insecure. This concept was applied by Dodis et al. in the context of secure key exchange (handshake phase), where the adversary wants to exfiltrate sensitive information by using a subverted client implementation. RFs are used as a means of "sanitizing" the...

Bitstream reverse engineering is traditionally associated with Intellectual Property (IP) theft. Another, less known, threat deriving from that is bitstream modification attacks. It has been shown that the secret key can be extracted from FPGA implementations of cryptographic algorithms by injecting faults directly into the bitstream. Such bitstream modification attacks rely on changing the content of Look Up Tables (LUTs). Therefore, related countermeasures aim to make the task...

Reverse engineering of integrated circuits, i.e., understanding the internals of IC, is required for many benign and malicious applications. Examples of the former are detection of patent infringements, hardware Trojans or IP-theft, as well as interface recovery and defect analysis, while malicious applications include IP-theft and finding insertion points for hardware Trojans. However, regardless of the application, the reverse engineer initially starts with a large unstructured netlist,...

Hardware obfuscation is widely used in practice to counteract reverse engineering. In recent years, low-level obfuscation via camouflaged gates has been increasingly discussed in the scientific community and industry. In contrast to classical high-level obfuscation, such gates result in recovery of an erroneous netlist. This technology has so far been regarded as a purely defensive tool. We show that low-level obfuscation is in fact a double-edged sword that can also enable stealthy...

Physically unclonable function (PUF) is a technology to generate a device-unique identifier using process variation. PUF enables a cryptographic key that appears only when the chip is active, providing an efficient countermeasure against reverse-engineering attacks. In this paper, we explore the data conversion that digitizes a physical quantity representing PUF’s uniqueness into a numerical value as a new attack surface. We focus on time-to-digital converter (TDC) that converts time...