Private set intersections are cryptographic protocols that compute the intersection of multiple parties' private sets without revealing elements that are not in the intersection. These protocols become less efficient when the number of parties grows, or the size of the sets increases. For this reason, many protocols are based on Bloom filters, which speed up the protocol by approximating the intersections, introducing false positives with a small but non-negligible probability. These false...

Light clients implement a simple solution for Bitcoin's scalability problem, as they do not store the entire blockchain but only the state of particular addresses of interest. To be able to keep track of the updated state of their addresses, light clients rely on full nodes to provide them with the required information. To do so, they must reveal information about the addresses they are interested in. This paper studies the two most common light client implementations, SPV and Neutrino with...

Redis (Remote Dictionary Server) is a general purpose, in-memory database that supports a rich array of functionality, including various Probabilistic Data Structures (PDS), such as Bloom filters, Cuckoo filters, as well as cardinality and frequency estimators. These PDS typically perform well in the average case. However, given that Redis is intended to be used across a diverse array of applications, it is crucial to evaluate how these PDS perform under worst-case scenarios, i.e., when...

As the field of genomics continues to expand and more sequencing data is gathered, genome analysis becomes increasingly relevant for many users. For example, a common scenario entails users trying to determine if their DNA samples are similar to DNA sequences hosted in a larger remote repository. Nevertheless, end users may be reluctant to upload their DNA sequences, while the owners of remote genomics repositories are unwilling to openly share their database. To address this challenge, we...

Boolean Searchable Symmetric Encryption (SSE) enables secure outsourcing of databases to an untrusted server in encrypted form and allows the client to execute secure Boolean queries involving multiple keywords. The leakage of keyword pair result pattern (KPRP) in a Boolean search poses a significant threat, which reveals the intersection of documents containing any two keywords involved in a search and can be exploited by attackers to recover plaintext information about searched keywords...

Creating an adversary resilient construction of the Learned Bloom Filter with provable guarantees is an open problem. We define a strong adversarial model for the Learned Bloom Filter. Our adversarial model extends an existing adversarial model designed for the Classical (i.e not ``Learned'') Bloom Filter by prior work and considers computationally bounded adversaries that run in probabilistic polynomial time (PPT). Using our model, we construct an adversary resilient variant of the Learned...

Boolean Searchable Symmetric Encryption (BSSE) enables users to perform retrieval operations on the encrypted data while sup- porting complex query capabilities. This paper focuses on addressing the storage overhead and privacy concerns associated with existing BSSE schemes. While Patel et al. (ASIACRYPT’21) and Bag et al. (PETS’23) introduced BSSE schemes that conceal the number of single keyword re- sults, both of them suffer from quadratic storage overhead and neglect the privacy of...

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...

A mutator set is a cryptographic data structure for authenticating operations on a changing set of data elements called items. Informally: - There is a short commitment to the set. - There are succinct membership proofs for elements of the set. - It is possible to update the commitment as well as the membership proofs with minimal effort as new items are added to the set or as existing items are removed from it. - Items cannot be removed before they were added. - It is...

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...

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...

A Bloom filter is a data structure that maintains a succinct and probabilistic representation of a set $S\subseteq U$ of elements from a universe $U$. It supports approximate membership queries. The price of the succinctness is allowing some error, namely false positives: for any $x\notin S$, it might answer `Yes' but with a small (non-negligible) probability. When dealing with such data structures in adversarial settings, we need to define the correctness guarantee and formalize the...

Time-based One-Time Password (TOTP) provides a strong second factor for user authentication. In TOTP, a prover authenticates to a verifier by using the current time and a secret key to generate an authentication token (or password) which is valid for a short time period. Our goal is to extend TOTP to the group setting, and to provide both authentication and privacy. To this end, we introduce a new authentication scheme, called Group TOTP (GTOTP), that allows the prover to prove that it is a...

We study the security of Probabilistic Data Structures (PDS) for handling Approximate Membership Queries (AMQ); prominent examples of AMQ-PDS are Bloom and Cuckoo filters. AMQ-PDS are increasingly being deployed in environments where adversaries can gain benefit from carefully selecting inputs, for example to increase the false positive rate of an AMQ-PDS. They are also being used in settings where the inputs are sensitive and should remain private in the face of adversaries who can...

Recent years have seen a strong uptick in both the prevalence and real-world consequences of false information spread through online platforms. At the same time, encrypted messaging systems such as WhatsApp, Signal, and Telegram, are rapidly gaining popularity as users seek increased privacy in their digital lives. The challenge we address is how to combat the viral spread of misinformation without compromising privacy. Our FACTS system tracks user complaints on messages obliviously, only...

Merkle tree is applied in diverse applications, namely, Blockchain, smart grid, IoT, Biomedical, financial transactions, etc., to verify authenticity and integrity. Also, the Merkle tree is used in privacy-preserving computing. However, the Merkle tree is a computationally costly data structure. It uses cryptographic string hash functions to partially verify the data integrity and authenticity of a data block. However, the verification process creates unnecessary network traffic because it...

In this paper, we present a concretely efficient protocol for private set intersection (PSI) in the multi-party setting using oblivious pseudorandom function (OPRF). In fact, we generalize the approach used in the work of Chase and Miao [CRYPTO 2020] towards deploying a lightweight multi-point OPRF construction for two-party PSI. Our protocol only includes oblivious transfer (OT) extension and garbled Bloom filter as its main ingredients and avoids computationally expensive operations. From...

Private set intersection (PSI) protocols allow a set of mutually distrustful parties, each holding a private set of items, to compute the intersection over all their sets, such that no other information is revealed. PSI has a wide variety of applications including online advertising (e.g., efficacy computation), security (e.g., botnet detection, intrusion detection), proximity testing (e.g., COVID-19 contact tracing), and more. Private set intersection is a rapidly developing area and there...

Public-key encryption (PKE) schemes or key-encapsulation mechanisms (KEMs) are fundamental cryptographic building blocks to realize secure communication protocols. There are several known transformations that generically turn weakly secure schemes into strongly (i.e., IND-CCA) secure ones. While most of these transformations require the weakly secure scheme to provide perfect correctness, Hofheinz, Hövelmanns, and Kiltz (HHK) (TCC 2017) have recently shown that variants of the...

In this paper, we propose a new private set intersection (PSI) protocol with bi-oblivious data transfer that computes the following functionality. One of the parties $P_1$ inputs a set of items $X$ and a set of data pairs $D_1 = \{ (d_0^j,d_1^j)\}$ and the other party $P_2$ inputs a set of items $Y$. While $P_1$ outputs nothing, $P_2$ outputs a set of data $D_2 = \{ d_{b_j}^j \mid b_j \in \{0,1\}\}$ dependent on the intersection of $X$ and $Y$. This functionality is generally required when...

Modern cryptographic protocols, such as TLS 1.3 and QUIC, can send cryptographically protected data in "zero round-trip times (0-RTT)", that is, without the need for a prior interactive handshake. Such protocols meet the demand for communication with minimal latency, but those currently deployed in practice achieve only rather weak security properties, as they may not achieve forward security for the first transmitted payload message and require additional countermeasures against replay...

We present a 2-party private set intersection (PSI) protocol which provides security against malicious participants, yet is almost as fast as the fastest known semi-honest PSI protocol of Kolesnikov et al. (CCS 2016). Our protocol is based on a new approach for two-party PSI, which can be instantiated to provide security against either malicious or semi-honest adversaries. The protocol is unique in that the only difference between the semi-honest and malicious versions is an instantiation...

Recently proposed searchable symmetric encryption (SSE) scheme HXT improves the OXT by avoiding the KPRP leakage at the cost of increasing the storage by two orders of magnitude. In this paper, we reconsider the principle of designing SSE protocols to prevent KPRP leakage. At first, we introduce a new primitive called subset membership check (SMC), where a set is encrypted such that its subset membership can be checked only through a protocol between Sender and Tester. The security of SMC...

Probabilistic data structures use space-efficient representations of data in order to (approximately) respond to queries about the data. Traditionally, these structures are accompanied by probabilistic bounds on query-response errors. These bounds implicitly assume benign attack models, in which the data and the queries are chosen non-adaptively, and independent of the randomness used to construct the representation. Yet probabilistic data structures are increasingly used in settings where...

In the area of cloud computing, judging the fulfillment of service-level agreements on a technical level is gaining more and more importance. To support this we introduce privacy preserving set relations as inclusiveness and disjointness based on Bloom filters. We propose to compose them in a slightly different way by applying a keyed hash function. Besides discussing the correctness of the set relations, we analyze how this impacts the privacy of the sets content as well as providing...

Proof-of-stake (PoS) blockchain protocols are emerging as one of the most promising alternative to the energy-consuming proof-of-work protocols. However, one particularly critical threat in the PoS setting is the well-known long-range attacks caused by secret key leakage (LRSL attack). Specifically, an adversary can attempt to corrupt the secret keys corresponding to accounts possessing substantial stake at some past moment such that double-spend or erase past transactions, violating the...

In this work, we discuss our successful efforts for industry deployment of a cryptographic secure computation protocol. The problem we consider is privately computing aggregate conversion rate of advertising campaigns. This underlying functionality can be abstracted as Private Intersection-Sum (PI-Sum) with Cardinality. In this setting two parties hold datasets containing user identifiers, and one of the parties additionally has an integer value associated with each of its user identifiers....

The recently proposed Oblivious Cross-Tags (OXT) protocol (CRYPTO 2013) has broken new ground in designing efficient searchable symmetric encryption (SSE) protocol with support for conjunctive keyword search in a single-writer single-reader framework. While the OXT protocol offers high performance by adopting a number of specialised data-structures, it also trades-off security by leaking ‘partial’ database information to the server. Recent attacks have exploited similar partial information...

Forward secrecy is considered an essential design goal of modern key establishment (KE) protocols, such as TLS 1.3, for example. Furthermore, efficiency considerations such as zero round-trip time (0-RTT), where a client is able to send cryptographically protected payload data along with the very first KE message, are motivated by the practical demand for secure low-latency communication. For a long time, it was unclear whether protocols that simultaneously achieve 0-RTT and full forward...

By allowing a large number of users to behave as readers or writers, Multi-User Searchable Encryption (MUSE) raises new security and performance challenges beyond the typical requirements of Symmetric Searchable Encryption (SSE). In this paper we identify two core mandatory requirements of MUSE protocols being privacy in face of users colluding with the CSP and low complexity for the users, pointing that no existing MUSE protocol satisfies these two requirements at the same time. We then...

Private set intersection (PSI) is a cryptographic technique that is applicable to many privacy-sensitive scenarios. For decades, researchers have been focusing on improving its efficiency in both communication and computation. However, most of the existing solutions are inefficient for an unequal number of inputs, which is common in conventional client-server settings. In this paper, we analyze and optimize the efficiency of existing PSI protocols to support precomputation so that they can...

We devise a virtual black-box (VBB) obfuscator for querying whether set elements are stored within Bloom filters, with security based on the Ring Learning With Errors (RLWE) problem and strongly universal hash functions. Our construction uses an abstracted encoding scheme that we instantiate using the Gentry, Gorbunov and Halevi (GGH15) multilinear map, with an explicit security reduction to RLWE. This represents an improvement on the functionality and security guarantees compared with the...

Recent work on searchable symmetric encryption (SSE) has focused on increasing its expressiveness. A notable example is the OXT construction (Cash et al., CRYPTO '13 ) which is the first SSE scheme to support conjunctive keyword queries with sub-linear search complexity. While OXT efficiently supports disjunctive and boolean queries that can be expressed in searchable normal form, it can only handle arbitrary disjunctive and boolean queries in linear time. This motivates the problem of...

Electronic information is increasingly often shared among unreliable entities. In this context, one interesting problem involves two parties that secretly want to determine intersection of their respective private data sets while none of them wish to disclose the whole set to other. One can adopt Private Set Intersection (PSI) protocol to address this problem preserving the associated security and privacy issues. This paper presents the first PSI protocol that achieves constant ($p(\kappa)$)...

Private set intersection (PSI) refers to a special case of secure two-party computation in which the parties each have a set of items and compute the intersection of these sets without revealing any additional information. In this paper we present improvements to practical PSI providing security in the presence of {\em malicious} adversaries. Our starting point is the protocol of Dong, Chen \& Wen (CCS 2013) that is based on Bloom filters. We identify a bug in their malicious-secure variant...

A private set intersection protocol consists of two parties, a Sender and a Receiver, each with a secret input set. The protocol aims to have the Receiver output an intersection of the two sets while keeping the elements in the sets secret. This thesis thoroughly analyzes four recently published set intersection protocols, where it explains each protocol and checks whether it satisfies its corresponding security definition. The first two protocols [PSZ14, PSSZ15a] use random oblivious...

AnNotify is a scalable service for private, timely and low-cost online notifications, based on anonymous communication, sharding, dummy queries, and Bloom filters. We present the design and analysis of AnNotify, as well as an evaluation of its costs. We outline the design of AnNotify and calculate the concrete advantage of an adversary observing multiple queries. We present a number of extensions, such as generic presence and broadcast notifications, and applications, including notifications...

Private set operation (PSO) protocols provide a natural way of securely performing operations on data sets, such that crucial details of the input sets are not revealed. Such protocols have an ever-increasing number of practical applications, particularly when implementing privacy-preserving data mining schemes. Protocols for computing private set operations have been prevalent in multi-party computation literature over the past decade, and in the case of private set intersection (PSI), have...

Sharing information to others is common nowadays, but the question is with whom to share. To address this problem, we propose the notion of secret transfer with access structure (STAS). STAS is a two-party computation protocol that enables the server to transfer a secret to a client who satisfies the prescribed access structure. In this paper, we focus on the case of STAS for threshold access structure, i.e. threshold secret transfer (TST). We also discuss how to replace it with linear...

Cloud data owners encrypt their documents before outsourcing to provide their privacy. They could determine a search control policy and delegate the ability of search token generation to the users whose attributes satisfy the search control policy. Verifiable attribute-based keyword search (VABKS) where the users can also verify the accuracy of cloud functionality is one of such schemes. In this paper, the first generic construction for VABKS is proposed. To this end, the notion of...

Many efficient data structures use randomness, allowing them to improve upon deterministic ones. Usually, their efficiency and correctness are analyzed using probabilistic tools under the assumption that the inputs and queries are independent of the internal randomness of the data structure. In this work, we consider data structures in a more robust model, which we call the adversarial model. Roughly speaking, this model allows an adversary to choose inputs and queries adaptively according...

We introduce Accountable Storage, a framework allowing a client with small local space to outsource n file blocks to an untrusted server and be able (at any point in time after outsourcing) to provably compute how many bits have been discarded by the server. Such protocols offer ``provable storage insurance" to a client: In case of a data loss, the client can be compensated with a dollar amount proportional to the damage that has occurred, forcing the server to be more ``accountable" for his...

Lightweight Bitcoin clients are gaining increasing adoption among Bitcoin users, owing to their reduced resource and bandwidth consumption. These clients support a simplified payment verification (SPV) mode as they are only required to download and verify a part of the block chain — thus supporting the usage of Bitcoin on constrained devices, such as smartphones. SPV clients rely on Bloom filters to receive transactions that are relevant to their local wallet. These filters embed all the...

The wide availability of inexpensive positioning systems made it possible to embed them into smartphones and other personal devices. This marked the beginning of location-aware applications, where users request personalized services based on their geographic position. The location of a user is, however, highly sensitive information: the user's privacy can be preserved if only the minimum amount of information needed to provide the service is disclosed at any time. While some applications,...

The increasing penetration of Online Social Networks (OSNs) prompts the need for effectively accessing and utilizing social networking information. In numerous applications, users need to make trust and/or access control decisions involving other (possibly stranger) users, and one important factor is often the existence of common social relationships. This motivates the need for secure and privacy-preserving techniques allowing users to assess whether or not they have mutual friends. This...

We study the problem of authenticating a \emph{dynamic table} with $n$ entries in the authenticated data structures model, which is related to memory checking. We present the first dynamic authenticated table that is \emph{update-optimal}, using a \emph{lattice-based} construction. In particular, the update time is $O(1)$, improving in this way the ``a priori'' $O(\log n)$ update bounds for previous constructions, such as the Merkle tree. Moreover, the space used by our data structure is...

RFID can be used for a variety of applications, e.g., to conveniently pay for public transportation. However, achieving security and privacy of payment is challenging due to the extreme resource restrictions of RFID tags. In this paper, we propose PSP -- a secure, RFID-based protocol for privacy-preserving payment. Similar to traditional electronic cash, the user of a tag can pay access to a metro using his tag and so called {coins} of a virtual currency. With PSP, tags do not need to store...

It is often necessary for two or more or more parties that do not fully trust each other to selectively share data. We propose a search scheme based on Bloom filters and Pohlig-Hellman encryption. A semi-trusted third party can transform one party's search queries to a form suitable for querying the other party's database, in such a way that neither the third party nor the database owner can see the original query. Furthermore, the encryption keys used to construct the Bloom filters are...

A secure index is a data structure that allows a querier with a ``trapdoor'' for a word x to test in O(1) time only if the index contains x; The index reveals no information about its contents without valid trapdoors, and trapdoors can only be generated with a secret key. Secure indexes are a natural extension of the problem of constructing data structures with privacy guarantees such as those provided by oblivious and history independent data structures. In this paper, we formally define a...