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...

Private set intersection (PSI) allows Sender holding a set \(X\) and Receiver holding a set \(Y\) to compute only the intersection \(X\cap Y\) for Receiver. We focus on a variant of PSI, called fuzzy PSI (FPSI), where Receiver only gets points in \(X\) that are at a distance not greater than a threshold from some points in \(Y\). Most current FPSI approaches first pick out pairs of points that are potentially close and then determine whether the distance of each selected pair is indeed...

Private set intersection (PSI) allows two mutually distrusting parties each holding a private set of elements, to learn the intersection of their sets without revealing anything beyond the intersection. Recent work (Badrinarayanan et al., PoPETS'22) initiates the study of updatable PSI (UPSI), which allows the two parties to compute PSI on a regular basis with sets that constantly get updated, where both the computation and communication complexity only grow with the size of the small...

Privacy set intersection (PSI) and private information retrieval (PIR) are important areas of research in privacy protection technology. One of the key tools for both is the oblivious pseudorandom function (OPRF). Currently, existing oblivious pseudorandom functions either focus solely on efficiency without considering quantum attacks, or are too complex, resulting in low efficiency. The aim of this paper is to achieve a balance: to ensure that the oblivious pseudorandom function can...

Private Set Intersection (PSI) enables a sender and a receiver to jointly compute the intersection of their sets without disclosing other information about items not in the intersection. However, in many cases of joint data analysis, it is not just the items outside the intersection that are sensitive but the items within it. To protect such sensitive information, prior work presents a Differentially Private version of PSI (DPSI) based on a circuit-PSI using Fully Homomorphic Encryption....

Many efficient custom protocols have been developed for two-party private set intersection (PSI), that allow the parties to learn the intersection of their private sets. However, these approaches do not yield efficient solutions in the dynamic setting when the parties’ sets evolve and the intersection has to be computed repeatedly. In this work we propose a new framework for this problem of updatable PSI — with elements being inserted and deleted — in the semihonest model based on structured...

Deduplication is a vital preprocessing step that enhances machine learning model performance and saves training time and energy. However, enhancing federated learning through deduplication poses challenges, especially regarding scalability and potential privacy violations if deduplication involves sharing all clients’ data. In this paper, we address the problem of deduplication in a federated setup by introducing a pioneering protocol, Efficient Privacy-Preserving Multi-Party Deduplication...

Oblivious Transfer (OT) is a fundamental cryptographic protocol with applications in secure Multi-Party Computation, Federated Learning, and Private Set Intersection. With the advent of quantum computing, it is crucial to develop unconditionally secure core primitives like OT to ensure their continued security in the post-quantum era. Despite over four decades since OT's introduction, the literature has predominantly relied on computational assumptions, except in cases using unconventional...

Multi-party computation (\textsf{MPC}) is a major research interest in modern cryptography, and Privacy Set Intersection (\textsf{PSI}) is an important research topic within \textsf{MPC}. Its main function is to allow two parties to compute the intersection of their private sets without revealing any other information. Therefore, \textsf{PSI} can be applied to various real-world scenarios, such as the Industrial Internet of Things (\textsf{IIOT}). Chase and Miao presented a paper on...

Secure equality testing and comparison are two important primitives that have been widely used in many secure computation scenarios, such as privacy-preserving machine learning, private set intersection, secure data mining, etc. In this work, we propose new constant-round two-party computation (2PC) protocols for secure equality testing and secure comparison. Our protocols are designed in the online/offline paradigm. Theoretically, for 32-bit integers, the online communication for our...

Structure-Aware Private Set Intersection (sa-PSI), recently introduced by Garimella et al. (Crypto'22), is a PSI variant where Alice's input set $S_A$ has a publicly known structure (for example, interval, ball or union of balls) and Bob's input $S_B$ is an unstructured set of elements. Prior work achieves sa-PSI where the communication cost only scales with the description size of $S_A$ instead of the set cardinality. However, the computation cost remains linear in the cardinality of $S_A$,...

Circuit Private Set Intersection (Circuit-PSI) allows two parties to compute any functionality $f$ on items in the intersection of their input sets without revealing any information about the intersection set. It is a well-known variant of PSI and has numerous practical applications. However, existing circuit-PSI protocols only provide security against \textit{semi-honest} adversaries. One straightforward solution is to extend a pure garbled-circuit-based PSI (NDSS'12) to a maliciously...

In many real-world scenarios, there are cases where a client wishes to check if a data element they hold is included in a set segmented across a large number of data holders. To protect user privacy, the client’s query and the data holders’ sets should remain encrypted throughout the whole process. Prior work on Private Set Intersection (PSI), Multi-Party PSI (MPSI), Private Membership Test (PMT), and Oblivious RAM (ORAM) falls short in this scenario in many ways. They either require...

Private Set Intersection (PSI) is a protocol where two parties with individually held confidential sets want to jointly learn (or secret-share) the intersection of these two sets and reveal nothing else to each other. In this paper, we introduce a natural extension of this notion to approximate matching. Specifically, given a distance metric between elements, an approximate PSI (Approx-PSI) allows to run PSI where ``close'' elements match. Assuming that elements are either ``close'' or...

Private set intersection (PSI) allows two parties to compute the intersection of their sets without revealing anything else. In some applications of PSI, a server holds a large set and runs a PSI protocol with multiple clients, each with its own smaller set. In this setting, existing protocols fall short: they either achieve only semi-honest security, or else require the server to run the protocol from scratch for each execution. We design an efficient protocol for this setting with...

Private set intersection (PSI) is a cryptographic functionality for two parties to learn the intersection of their input sets, without leaking any other information. Circuit-PSI is a stronger PSI functionality where the parties learn only a secret-shared form of the desired intersection, thus without revealing the intersection directly. These secret shares can subsequently serve as input to a secure multiparty computation of any function on this intersection. In this paper we consider...

Third-party private set intersection (PSI) enables two parties, each holding a private set to compute their intersection and reveal the result only to an inputless third party. In this paper, we present an efficient third-party PSI protocol requiring only 3 communication rounds, while significantly lowering the computational workload compared to prior work. Our work is motivated by real-world applications such as contact tracing whereby expedition is essential while concurrently preserving...

Secure multi-party computation aims to allow a set of players to compute a given function on their secret inputs without revealing any other information than the result of the computation. In this work, we focus on the design of secure multi-party protocols for shared polynomial operations. We consider the classical model where the adversary is honest-but-curious, and where the coefficients (or any secret values) are either encrypted using an additively homomorphic encryption scheme or...

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

An Oblivious Pseudo-Random Function (OPRF) is a two-party protocol for jointly evaluating a Pseudo-Random Function (PRF), where a user has an input x and a server has an input k. At the end of the protocol, the user learns the evaluation of the PRF using key k at the value x, while the server learns nothing about the user's input or output. OPRFs are a prime tool for building secure authentication and key exchange from passwords, private set intersection, private information retrieval,...

Multiparty private set intersection (mPSI) protocol is capable of finding the intersection of multiple sets securely without revealing any other information. However, its limitation lies in processing only those elements present in every participant's set, which proves inadequate in scenarios where certain elements are common to several, but not all, sets. In this paper, we introduce an innovative variant of the mPSI protocol named unbalanced quorum PSI to fill in the gaps of the mPSI...

Traditional private set intersection (PSI) involves a receiver and a sender holding sets $X$ and $Y$, respectively, with the receiver learning only the intersection $X\cap Y$. We turn our attention to its fuzzy variant, where the receiver holds \(|X|\) hyperballs of radius \(\delta\) in a metric space and the sender has $|Y|$ points. Representing the hyperballs by their center, the receiver learns the points $x\in X$ for which there exists $y\in Y$ such that $\mathsf{dist}(x,y)\leq...

In this paper, we study two problems: oblivious compression and decompression of ciphertexts. In oblivious compression, a server holds a set of ciphertexts with a subset of encryptions of zeroes whose positions are only known to the client. The goal is for the server to effectively compress the ciphertexts obliviously, while preserving the non-zero plaintexts and without learning the plaintext values. For oblivious decompression, the client, instead, succinctly encodes a sequence of...

Private Set Intersection (PSI) is a widely used protocol that enables two parties to securely compute a function over the intersected part of their shared datasets and has been a significant research focus over the years. However, recent studies have highlighted its vulnerability to Set Membership Inference Attacks (SMIA), where an adversary might deduce an individual's membership by invoking multiple PSI protocols. This presents a considerable risk, even in the most stringent versions of...

Laconic cryptography enables secure two-party computation (2PC) on unbalanced inputs with asymptotically-optimal communication in just two rounds of communication. In particular, the receiver (who sends the first-round message) holds a long input and the sender (who sends the second-round message) holds a short input, and the size of their communication to securely compute a function on their joint inputs only grows with the size of the sender's input and is independent of the receiver's...

We introduce $\mathsf{ChalametPIR}$: a single-server Private Information Retrieval (PIR) scheme supporting fast, low-bandwidth \emph{keyword} queries, with a conceptually very simple design. In particular, we develop a generic framework for converting PIR schemes for index queries over flat arrays (based on Learning With Errors) into keyword PIR. This involves representing a key-value map using any probabilistic filter that permits reconstruction of elements from inclusion queries (e.g....

Federated Learning (FL) is a data-minimization approach enabling collaborative model training across diverse clients with local data, avoiding direct data exchange. However, state-of-the-art FL solutions to identify fraudulent financial transactions exhibit a subset of the following limitations. They (1) lack a formal security definition and proof, (2) assume prior freezing of suspicious customers’ accounts by financial institutions (limiting the solutions’ adoption), (3) scale poorly,...

Private set intersection protocols allow two parties with private sets of data to compute the intersection between them without leaking other information about their sets. These protocols have been studied for almost 20 years, and have been significantly improved over time, reducing both their computation and communication costs. However, when more than two parties want to compute a private set intersection, these protocols are no longer applicable. While extensions exist to the multi-party...

Private Set Intersection Cardinality(PSI-CA) is a type of secure two-party computation. It enables two parties, each holding a private set, to jointly compute the cardinality of their intersection without revealing any other private information about their respective sets. In this paper, we manage to break two PSI-CA protocols by recovering the specific intersection items in polynomial time. Among them, the PSI-CA protocol proposed by De Cristofaro et al. in 2012 is the most popular...

We present a new method for doing multi-party private set intersection against a malicious adversary, which reduces the total communication cost to $ O(nl\kappa) $. Additionally, our method can also be used to build a multi-party Circuit-PSI without payload. Our protocol is based on Vector-OLE(VOLE) and oblivious key-value store(OKVS). To meet the requirements of the protocol, we first promote the definition of VOLE to a multi-party version. After that, we use the new primitive to construct...

Private Set Intersection (PSI) is a well-studied secure two-party computation problem in which a client and a server want to compute the intersection of their input sets without revealing additional information to the other party. With this work, we present nested Cuckoo hashing, a novel hashing approach that can be combined with additively homomorphic encryption (AHE) to construct an efficient PSI protocol for unbalanced input sets. We formally prove the security of our protocol against...

Symmetric Private Information Retrieval (SPIR) is a protocol that protects privacy during data transmission. However, the existing SPIR focuses only on the privacy of the data to be requested on the server, without considering practical factors such as the payload that may be present during data transmission. This could seriously prevent SPIR from being applied to many complex data scenarios and hinder its further expansion. To solve such problems, we propose a primitive (PSKPIR) for...

Circuit-based Private Set Intersection (circuit-PSI) empowers two parties, a client and a server, each with input sets $X$ and $Y$, to securely compute a function $f$ on the intersection $X \cap Y$ while preserving the confidentiality of $X \cap Y$ from both parties. Despite the recent proposals of computationally efficient circuit-PSI protocols, they primarily focus on the balanced scenario where $|X|$ is similar to $|Y|$. However, in many practical situations, a circuit-PSI protocol may...

Symmetric Private Information Retrieval (SPIR) is a stronger PIR protocol that ensures both client and server privacy. In many cases, the client needs authorization from the data subject before querying data. However, this also means that the server can learn the identity of the data subject. To solve such problems, we propose a new SPIR primitive, called authorized symmetric keyword information retrieval protocol (ASKPIR). Specifically, we designed an efficient DID identification algorithm...

Multi-party private set union (MPSU) allows \(k(k\geq 3)\) parties, each holding a dataset of known size, to compute the union of their sets without revealing any additional information. Although two-party PSU has made rapid progress in recent years, applying its effective techniques to the multi-party setting would render information leakage and thus cannot be directly extended. Existing MPSU protocols heavily rely on computationally expensive public-key operations or generic secure...

This study delves into secure computations for set intersections using fully homomorphic encryption (FHE) within the semi-honest setting. Our protocols facilitate joint computations between two parties, each holding a set of inputs denoted as $N_s$ and $N_r$ in size, respectively. The primary objective is to determine various functionalities, such as intersection size and sum, while maintaining data confidentiality. These functionalities extend the classic private set intersection (PSI) and...

Structure-Aware private set intersection (sa-PSI) is a variant of PSI where Alice's input set $A$ has some publicly known structure, Bob's input $B$ is an unstructured set of points, and Alice learns the intersection $A \cap B$. sa-PSI was recently introduced by Garimella et al. (Crypto 2022), who described a semi-honest protocol with communication that scales with the description size of Alice's set, instead of its cardinality. In this paper, we present the first sa-PSI protocol secure...

The Internet of Things (IoT)-enabled ride sharing is one of the most transforming and innovative technologies in the transportation industry. It has myriads of advantages, but with increasing demands there are security concerns as well. Traditionally, cryptographic methods are used to address the security and privacy concerns in a ride sharing system. Unfortunately, due to the emergence of quantum algorithms, these cryptographic protocols may not remain secure. Hence, there is a...

We instantiate the hash-then-evaluate paradigm for pseudorandom functions (PRFs), $\mathsf{PRF}(k, x) := \mathsf{wPRF}(k, \mathsf{RO}(x))$, which builds a PRF $\mathsf{PRF}$ from a weak PRF $\mathsf{wPRF}$ via a public preprocessing random oracle $\mathsf{RO}$. In applications to secure multiparty computation (MPC), only the low-complexity wPRF performs secret-depending operations. Our construction replaces RO by $f(k_H , \mathsf{elf}(x))$, where $f$ is a non-adaptive PRF and the key $k_H$...

Private computation on (labeled) set intersection (PCSI/PCLSI) is a secure computation protocol that allows two parties to compute fine-grained functions on set intersection, including cardinality, cardinality-sum, secret shared intersection, and arbitrary functions. Recently, some computationally efficient PCSI protocols have emerged, but a limitation of these protocols is the communication complexity, which scales (super)-linear with the size of the large set. This is of particular concern...

Circuit-based Private Set Intersection (circuit-PSI) refers to cryptographic protocols that let two parties with input set $X$ and $Y$ compute a function $f$ over the intersection set $X \cap Y$, without revealing any other information. The research efforts for circuit-PSI mainly focus on the case where input set sizes $|X|$ and $|Y|$ are similar so far, and they scale poorly for extremely unbalanced set sizes $|X| \gg |Y|$. Recently, Lepoint \textit{et al.} (ASIACRYPT'21) proposed the first...

Considering password-based authentication technique, password memorability is a real challenge on users. Hence, password reuse across different web applications is a common trend among users which makes websites vulnerable to credential stuffing attack. A solution as password manager helps the users to create random passwords for different websites on the user machine. However, it has practical challenges. Password database breach detection is another related and challenging task....

Private-ID (PID) protocol enables two parties, each holding a private set of items, to privately compute a set of random universal identifiers (UID) corresponding to the records in the union of their sets, where each party additionally learns which UIDs correspond to which items in its set but not if they belong to the intersection or not. PID is very useful in the privacy computation of databases query, e.g. inner join and join for compute. Known PID protocols all assume the input of both...

Given $\ell$ parties with sets $X_1, \dots, X_\ell$ of size $n$, we would like to securely compute the intersection $\cap_{i=1}^\ell X_i$, if it is larger than $n-t$ for some threshold $t$, without revealing any other additional information. It has previously been shown (Ghosh and Simkin, Crypto 2019) that this function can be securely computed with a communication complexity that only depends on $t$ and in particular does not depend on $n$. For small values of $t$, this results in protocols...

In this paper, we study oblivious key-value stores (OKVS) that enable encoding n key-value pairs into length $m$ encodings while hiding the input keys. The goal is to obtain high rate, $n/m$, with efficient encoding and decoding algorithms. We present $\mathsf{RB\text{-}OKVS}$ built on random band matrices that obtains near-optimal rates as high as 0.97 whereas prior works could only achieve rates up to 0.81 with similar encoding times. Using $\mathsf{RB\text{-}OKVS}$, we obtain...

Mobile contact discovery is a convenience feature of messengers such as WhatsApp or Telegram that helps users to identify which of their existing contacts are registered with the service. Unfortunately, the contact discovery implementation of many popular messengers massively violates the users' privacy as demonstrated by Hagen et al. (NDSS '21, ACM TOPS '23). Unbalanced private set intersection (PSI) protocols are a promising cryptographic solution to realize mobile private contact...

Private set intersection (PSI) is one of the most extensively studied instances of secure computation. PSI allows two parties to compute the intersection of their input sets without revealing anything else. Other useful variants include PSI-Payload, where the output includes payloads associated with members of the intersection, and PSI-Sum, where the output includes the sum of the payloads instead of individual ones. In this work, we make two related contributions. First, we construct...

Private set intersection (PSI) enables two parties, each holding a private set to compute their intersection without revealing other information in the process. We introduce a variant of conventional PSI termed as third-party PSI, whereby the intersection output of the two parties is only known to an inputless third party. In this setting, the two parties who participate in the protocol have no knowledge of the intersection result or any information of the set content of the other party. In...

Polynomial commitment schemes allow a prover to commit to a polynomial and later reveal the evaluation of the polynomial on an arbitrary point along with proof of validity. This object is central in the design of many cryptographic schemes such as zero-knowledge proofs and verifiable secret sharing. In the standard definition, the polynomial is known to the prover whereas the evaluation points are not private. In this paper, we put forward the notion of private polynomial commitments that...

Bottleneck complexity is an efficiency measure of secure multiparty computation (MPC) introduced by Boyle et al. (ICALP 2018) to achieve load-balancing. Roughly speaking, it is defined as the maximum communication complexity required by any player within the protocol execution. Since it was shown to be impossible to achieve sublinear bottleneck complexity in the number of players $n$ for all functions, a prior work constructed MPC protocols with low bottleneck complexity for specific...

Oblivious Pseudorandom Functions (OPRFs) are an elementary building block in cryptographic and privacy-preserving applications. However, while there are numerous pre-quantum secure OPRF constructions, few options exist in a post-quantum secure setting, and of those even fewer are practical for modern-day applications. In this work, we focus on isogeny group actions, as the associated low bandwidth leads to efficient constructions. Our results focus on the Naor-Reingold OPRF. We introduce...

In this paper, we propose the first linear two-party secure-computation private set intersection (PSI) protocol, in the semi-honest adversary model, computing the following functionality. One of the parties ($P_X$) inputs a set of items $X = \{x_j \mid 1 \le j \le n_X\}$, whereas the other party ($P_Y$) inputs a set of items $Y = \{y_i \mid 1\le i \le n_Y \}$ and a set of corresponding data pairs $D_Y = \{ (d_i^0,d_i^1) \mid 1 \le i \le n_Y\}$ having the same cardinality with $Y$. While...

Private set intersection (PSI) is a cryptographic primitive that allows two or more parties to learn the intersection of their input sets and nothing else. In this paper, we present a private set intersection protocol based on a new secure multi-party quantum protocol for greatest common divisor (GCD). The protocol is mainly inspired by the recent quantum private set union protocol based on least common multiple by Liu, Yang, and Li. Performance analysis guarantees the correctness and it...

Laconic cryptography is an emerging paradigm that enables cryptographic primitives with sublinear communication complexity in just two messages. In particular, a two-message protocol between Alice and Bob is called laconic if its communication and computation complexity are essentially independent of the size of Alice's input. This can be thought of as a dual notion of fully-homomorphic encryption, as it enables "Bob-optimized" protocols. This paradigm has led to tremendous progress in...

This paper proposes Prism, Private Verifiable Set Computation over Multi-Owner Outsourced Databases, a secret sharing based approach to compute private set operations (i.e., intersection and union), as well as aggregates over outsourced databases belonging to multiple owners. Prism enables data owners to pre-load the data onto non-colluding servers and exploits the additive and multiplicative properties of secret-shares to compute the above-listed operations in (at most) two rounds of...

In Private Set Intersection protocols (PSIs), a non-empty result always reveals something about the private input sets of the parties. Moreover, in various variants of PSI, not all parties necessarily receive or are interested in the result. Nevertheless, to date, the literature has assumed that those parties who do not receive or are not interested in the result still contribute their private input sets to the PSI for free, although doing so would cost them their privacy. In this work, for...

Integrating private set intersection (PSI) protocols within real-world data workflows, software applications, or web services can be challenging. This can occur because data contributors and result recipients do not have the technical expertise, information technology infrastructure, or other resources to participate throughout the execution of a protocol and/or to incur all the communication costs associated with participation. Furthermore, contemporary workflows, applications, and services...

We introduce the first candidate Lattice-based designated verifier (DV) zero knowledge sUccinct Non-interactive Argument (ZK-SNARG) protocol, LUNA, with quasi-optimal proof length (quasi-linear in the security/privacy parameter). By simply relying on mildly stronger security assumptions, LUNA is also a candidate ZK-SNARK (i.e. argument of knowledge). LUNA achieves significant improvements in concrete proof sizes, reaching below 6 KB (compared to >32 KB in prior work) for 128-bit...

We present a three-party sorting protocol secure against passive and active adversaries in the honest majority setting. The protocol can be easily combined with other secure protocols which work on shared data, and thus enable different data analysis tasks, such as private set intersection of shared data, deduplication, and the identification of heavy hitters. The new protocol computes a stable sort. It is based on radix sort and is asymptotically better than previous secure sorting...

The privacy set intersection (PSI) protocol with the oblivious pseudorandom function (OPRF) as the core component is a crucial member of PSI family, and the most efficient PSI protocol at present also belongs to this category. Based on DDH assumption, Hash Diffie-Hellman (HashDH) PSI is one of the most classical PSI protocols. Benefiting by its low communication overhead, it still has tremendous research value today. The OPRF subprotocol at the bottom of classical DH-PSI protocol falls into...

We introduce and investigate the privacy-preserving version of collaborative data cleaning. With collaborative data cleaning, two parties want to reconcile their data sets to filter out badly classified, misclassified data items. In the privacy-preserving (private) version of data cleaning, the additional security goal is that parties should only learn their misclassified data items, but nothing else about the other party's data set. The problem of private data cleaning is essentially a...

Private information retrieval (PIR) is a cryptographic protocol that enables a wide range of privacy-preserving applications. Despite being extensively studied for decades, it is still not efficient enough to be used in practice. In this paper, we propose a novel PIR protocol named PIRANA, based on the recent advances in constant-weight codes. It is up to 188.6× faster than the original constant-weight PIR (presented in Usenix SEC '22). Most importantly, PIRANA naturally supports...

We initiate the study of Private Certifier Intersection (PCI), which allows mutually distrusting parties to establish a trust basis for cross-validation of claims if they have one or more trust authorities (certifiers) in common. This is one of the essential requirements for verifiable presentations in Web 3.0, since it provides additional privacy without compromising on decentralization. A PCI protocol allows two or more parties holding certificates to identify a common set of certifiers...

Pushes for increased power of Law Enforcement (LE) for data retention and centralized storage result in legal challenges with data protection law and courts - and possible violations of the right to privacy. This is motivated by a desire for better cooperation and exchange between LE Agencies (LEAs), which is difficult due to data protection regulations, was identified as a main factor of major public security failures, and is a frequent criticism of LE. Secure Multi-Party Computation...

In this paper, we propose a new protocol for private computation on set intersection (PCI) which is an extension of private set intersection (PSI). In PSI, each party has a private set and both want to securely compute the intersection of their sets such that only the result is revealed and nothing else. In PCI, we want to additionally apply a private computation on the result. The goal is to reveal only the result of such a secure evaluation on the intersection and nothing else. We...

In two-party private set intersection (PSI), Alice holds a set $X$, Bob holds a set $Y$, and they learn (only) the contents of $X \cap Y$. We introduce structure-aware PSI protocols, which take advantage of situations where Alice's set $X$ is publicly known to have a certain structure. The goal of structure-aware PSI is to have communication that scales with the description size of Alice's set, rather its cardinality. We introduce a new generic paradigm for structure-aware...

Private function evaluation (PFE) is a special type of MPC protocols that, in addition to the input privacy, can preserve the function privacy. In this work, we propose a PFE scheme for RAM. In particular, we first design an efficient 4-server distributed ORAM scheme with amortized communication $O(\log n)$ per access (both reading and writing). We then simulate a RISC RAM machine over the MPC platform, hiding (i) the memory access pattern, (ii) the machine state (including registers,...

Solitary output secure computation models scenarios, where a single entity wishes to compute a function over an input that is distributed among several mutually distrusting parties. The computation should guarantee some security properties, such as correctness, privacy, and guaranteed output delivery. Full security captures all these properties together. This setting is becoming very important, as it is relevant to many real-world scenarios, such as service providers wishing to learn some...

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...

Private Set Intersection (PSI) allows a set of mutually distrustful parties, each holds a private data set, to compute the intersection of all sets, such that no information is revealed except for the intersection. The state-of-the-art PSI protocol (Garimella et al., CRYPTO'21) in the multi-party setting tolerating any number of malicious corruptions requires the communication bandwidth of $O(n\ell|\mathbb{F}|)$ bits for the central party $P_0$ due to the star architecture, where $n$ is the...

We describe a new paradigm for multi-party private set intersection cardinality (\psica) that allows $n$ parties to compute the intersection size of their datasets without revealing any additional information. We explore a variety of instantiations of this paradigm. Our protocols avoid computationally expensive public-key operations and are secure in the presence of a semi-honest adversary. We demonstrate the practicality of our \psica\ with an implementation. For $n=16$ parties with...

Today, our society produces massive amounts of data, part of which are strictly private. So, a long line of research has worked to design protocols that perform functions on such private data without revealing them. One function that has attracted significant interest is a multi-party private set operation, where each party's input is a set. The parties commonly intend to compute these sets' collective intersection (MPSI) or union (MPSU), which finds uses in various applications, including...

We study the problem of private set union in the two-party setting, providing several new constructions. We consider the case where one party is designated to receive output. In the semi-honest setting, we provide a four-round protocol and two-round protocol, each with two variants. Our four-round protocol focusing on runtime out-performs the state-of-the-art in runtime for the majority of the medium bandwidth settings ($100$Mbps) and the large set size ($\geq 2^{20}$) settings, with a...

Learning parity with noise (LPN) has been widely studied and used in cryptography. It was recently brought to new prosperity since Boyle et al. (CCS'18), putting LPN to a central role in designing secure multi-party computation, zero-knowledge proofs, private set intersection, and many other protocols. In this paper, we thoroughly studied the security of LPN problems in this particular context. We found that some important aspects have long been ignored and many conclusions from classical...

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...

The problem of Secure Merge consists of combining two sorted lists (which are either held separately by two parties, or secret-shared among two or more parties), and outputting a single merged (sorted) list, secret-shared among all parties. Just as insecure algorithms for comparison-based sorting are slower than merging (i.e., for lists of size $n$, $\Theta(n \log n)$ versus $\Theta(n)$), we explore whether the analogous separation exists for secure protocols; namely, if there exist...

Private set intersection (PSI) allows two parties, who each hold a set of items, to learn which items they have in common, without revealing anything about their other items. Some applications of PSI would be better served by revealing only one common item, rather than the entire set of all common items. In this work we develop simple special-purpose protocols for privately finding one common item (FOCI) from the intersection of two sets. The protocols differ in how that item is chosen ---...

Private set-intersection (PSI) is one of the most practically relevant special-purpose secure multiparty computation tasks, as it is motivated by many real-world applications. In this paper we present a new private set-intersection protocol which is laconic, meaning that the protocol only has two rounds and that the first message is independent of the set sizes. Laconic PSI can be useful in applications, where servers with large sets would like to learn the intersection of their set with...

We design several new protocols for private set intersection (PSI) with active security: one for the two party setting, and two protocols for the multi-party setting. In recent years, the state-of-the-art protocols for two party PSI have all been built from OT-extension. This has led to extremely efficient protocols that provide correct output to one party;~seemingly inherent to the approach, however, is that there is no efficient way to relay the result to the other party with a provable...

Private join and compute (PJC) is a paradigm where two parties owing their private database securely join their databases and compute a function over the combined database. Inner product PJC, introduced by Lepoint et al. (Asiacrypt'21), is a class of PJC that has a wide range of applications such as secure analysis of advertising campaigns. In this computation, two parties, each of which has a set of identifier-value pairs, compute the inner product of the values after the (inner) join of...

We introduce new protocols for private set intersection (PSI), building upon recent constructions of pseudorandom correlation generators, such as vector-OLE and ring-OLE. Our new constructions improve over the state of the art on several aspects, and perform especially well in the setting where the parties have databases with small entries. We obtain three main contributions: 1. We introduce a new semi-honest PSI protocol that combines subfield vector-OLE with hash-based PSI. Our protocol...

We present new semi-honest and malicious secure PSI protocols that outperform all prior works by several times in both communication and running time. For example, our semi-honest protocol for $n=2^{20}$ can be performed in 0.37 seconds compared to the previous best of 2 seconds (Kolesnikov et al., CCS 2016). This can be further reduced to 0.16 seconds with 4 threads, a speedup of $12\times$. Similarly, our protocol sends $187n$ bits compared to $426n$ bits of the next most communication...

Motivated by the recent advances in practical secure computation, we design and implement a framework for scaling solutions for the problem of private set intersection (PSI) into the realm of big data. A protocol for PSI enables two parties each holding a set of elements to jointly compute the intersection of these sets without revealing the elements that are not in the intersection. Following a long line of research, recent protocols for PSI only have $\approx 5\times$ computation and...

Recent new constructions of rate-1 OT [Döttling, Garg, Ishai, Malavolta, Mour, and Ostrovsky, CRYPTO 2019] have brought this primitive under the spotlight and the techniques have led to new feasibility results for private-information retrieval, and homomorphic encryption for branching programs. The receiver communication of this construction consists of a quadratic (in the sender's input size) number of group elements for a single instance of rate-1 OT. Recently [Garg, Hajiabadi, Ostrovsky,...

—Many solutions have been proposed to improve manual contact tracing for infectious diseases through automation. Privacy is crucial for the deployment of such a system as it greatly influences adoption. Approaches for digital contact tracing like Google Apple Exposure Notification (GAEN) protect the privacy of users by decentralizing risk scoring. But GAEN leaks information about diagnosed users as ephemeral pseudonyms are broadcast to everyone. To combat deanonymisation based on the time of...

Secure inference allows a server holding a machine learning (ML) inference algorithm with private weights, and a client with a private input, to obtain the output of the inference algorithm, without revealing their respective private inputs to one another. While this problem has received plenty of attention, existing systems are not applicable to a large class of ML algorithms (such as in the domain of Natural Language Processing) that perform featurization as their first step. In this...

Circuit-based private set intersection (circuit-PSI) enables two parties with input set $X$ and $Y$ to compute a function $f$ over the intersection set $X \cap Y$, without revealing any other information. State-of-the-art protocols for circuit-PSI commonly involves a procedure that securely checks whether two input strings are equal and outputs an additive share of the equality result. This procedure is typically performed by generic two party computation protocols, and its cost occupies...

Private set intersection (PSI) allows two mutually distrusting parties each with a set as input, to learn the intersection of both their sets without revealing anything more about their respective input sets. Traditionally, PSI studies the static setting where the computation is performed only once on both parties' input sets. We initiate the study of updatable private set intersection (UPSI), which allows parties to compute the intersection of their private sets on a regular basis with sets...

We address the problem of multiparty private set intersection against a malicious adversary. First, we show that when one can assume no collusion amongst corrupted parties then there exists an extremely efficient protocol given only symmetric-key primitives. Second, we present a protocol secure against an adversary corrupting any strict subset of the parties. Our protocol is based on the recently introduced primitives: oblivious programmable PRF (OPPRF) and oblivious key-value store...

We describe a protocol for two-party private set intersection (PSI) based on Diffie-Hellman key agreement. The protocol is proven secure against malicious parties, in the ideal permutation + random oracle model. For small sets (500 items or fewer), our protocol requires the least time and communication of any known PSI protocol, even ones that are only semi-honest secure and ones that are not based on Diffie-Hellman. It is one of the few significant improvements to the 20-year old classical...

It is known that fully homomorphic encryption (FHE) can be used to build efficient (labeled) Private Set Intersection protocols in the unbalanced setting, where one of the sets is much larger than the other (Chen et al. (CCS'17, CCS'18)). In this paper we demonstrate multiple algorithmic improvements upon these works. In particular, our protocol has an asymptotically better computation cost, requiring only $O(\sqrt{|X|})$ homomorphic multiplications, and communication complexity sublinear in...

Private Set Intersection protocols (PSIs) allow parties to compute the intersection of their private sets, such that nothing about the sets’ elements beyond the intersection is revealed. PSIs have a variety of applications, primarily in efficiently supporting data sharing in a privacy-preserving manner. At Eurocrypt 2019, Ghosh and Nilges pro- posed three efficient PSIs based on the polynomial representation of sets and proved their security against active adversaries. In this work, we show...

Oblivious Transfer (OT) is a fundamental primitive in cryptography, supporting protocols such as Multi-Party Computation and Private Set Intersection (PSI), that are used in applications like contact discovery, remote diagnosis and contact tracing. Due to its fundamental nature, it is utterly important that its execution is secure even if arbitrarily composed with other instances of the same, or other protocols. This property can be guaranteed by proving its security under the Universal...

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...

Many recent private set intersection (PSI) protocols encode input sets as polynomials. We consider the more general notion of an oblivious key-value store (OKVS), which is a data structure that compactly represents a desired mapping $k_i \mapsto v_i$. When the $v_i$ values are random, the OKVS data structure hides the $k_i$ values that were used to generate it. The simplest (and size-optimal) OKVS is a polynomial $p$ that is chosen using interpolation such that $p(k_i)=v_i$. We initiate...

Ridesharing is revolutionizing the transportation industry in many countries. Yet, the state of the art is based on heavily centralized services and platforms, where the service providers have full possession of the users’ location data. Recently, researchers have started addressing the challenge of enabling privacy-preserving ridesharing. The initial proposals, however, have shortcomings, as some rely on a central party, some incur high performance penalties, and most do not consider time...

We extend two-party private set union for secure computation, by considering matching between records having multiple identifiers (or keys), for example email and phone. In the classical setting of this problem, two parties want to perform various downstream computations on the union of two datasets. The union is computed by joining two datasets with the help of a single agreed upon identifier, say email. By extending this to joining records with multiple identifiers, we bring it much closer...

Consider a server with a large set $S$ of strings $\{x_1,x_2, \dots,x_N\}$ that would like to publish a small hash $h$ of its set $S$ such that any client with a string $y$ can send the server a short message allowing it to learn $y$ if $y \in S$ and nothing otherwise. In this work, we study this problem of two-round private set intersection (PSI) with low (asymptotically optimal) communication cost, or what we call laconic private set intersection ($\ell$PSI) and its extensions. This...

Contact tracing has emerged as a powerful and effective measure to curb the spread of contagious diseases. It is a robust tool, but on the downside, it possesses a risk of privacy violations as contact tracing requires gathering a lot of personal information. So there is a need for a cryptographic primitive that obfuscate the personal data of the user. Taking everything into account, private set intersection seems to be the natural choice to address the problem. Nearly all of the existing...

Functional encryption (FE) is a new paradigm of public key encryption that can control the exposed information of plaintexts by supporting computation on encrypted data. In this paper, we propose efficient multi-client FE (MCFE) schemes that compute the set intersection of ciphertexts generated by two clients. First, we propose an MCFE scheme that calculates the set intersection cardinality (MCFE-SIC) and prove its static security under dynamic assumptions. Next, we extend our MCFE-SIC...