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

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...

Private Information Retrieval (PIR) permits clients to query entries from a public database hosted on untrusted servers in a privacy-preserving manner. Traditional PIR model suffers from high computation and/or bandwidth cost due to entire database processing for privacy. Recently, Online-Offline PIR (OO-PIR) has been suggested to improve the practicality of PIR, where query-independent materials are precomputed beforehand to accelerate online access. While state-of-the-art OO-PIR schemes...

In this paper, we introduce a new framework for constructing linkable ring signatures (LRS). Our framework is based purely on signatures of knowledge (SoK) which allows one to issue signatures on behalf of any NP-statement using the corresponding witness. Our framework enjoys the following advantages: (1) the security of the resulting LRS depends only on the security of the underlying SoK; (2) the resulting LRS naturally supports online/offline signing (resp. verification), where the output...

An important research direction in secure multi-party computation (MPC) is to improve the efficiency of the protocol. One idea that has recently received attention is to consider a slightly weaker security model than full malicious security -- the so-called setting of $\textit{covert security}$. In covert security, the adversary may cheat but only is detected with certain probability. Several works in covert security consider the offline/online approach, where during a costly offline phase...

We define the security notion of (strong) collision resistance for chameleon hash functions in the multi-user setting ((S-)MU-CR security). We also present three constructions, CHF_dl, CHF_rsa and CHF_fac, and prove their tight S-MU-CR security based on the discrete logarithm, RSA and factoring assumptions, respectively. In applications, our tightly S-MU-CR secure chameleon hash functions help us to lift a signature scheme from (weak) unforgeability to strong unforgeability in the multi-user...

Ciphertext-policy attribute-based encryption is a versatile primitive that has been considered extensively to securely manage data in practice. Especially completely unbounded schemes are attractive, because they do not restrict the sets of attributes and policies. So far, any such schemes that support negations in the access policy or that have online/offline extensions have an inefficient decryption algorithm. In this work, we propose GLUE (Generalized, Large-universe, Unbounded and...

In recent years, lattice-based secure multi-party computation (MPC) has seen a rise in popularity and is used more and more in large scale applications like privacy-preserving cloud computing, electronic voting, or auctions. Many of these applications come with the following high security requirements: a computation result should be publicly verifiable, with everyone being able to identify a malicious party and hold it accountable, and a malicious party should not be able to corrupt the...

We consider private function evaluation (PFE) in malicious adversary model. Current state-of-the-art in PFE from Valiant's universal circuits (Liu, Yu, et al., CRYPTO 2021) does not avoid the logarithmic factor in circuit size. In constructing linear active PFE, one essential building block is to prove the correctness of an extended permutation (EP, Mohassel and Sadeghian at EUROCRYPT 2013) by zero-knowledge protocols with linear complexity. The linear instantiation...

This work describes the Mitaka signature scheme: a new hash-and-sign signature scheme over NTRU lattices which can be seen as a variant of NIST finalist Falcon. It achieves comparable efficiency but is considerably simpler, online/offline, and easier to parallelize and protect against side-channels, thus offering significant advantages from an implementation standpoint. It is also much more versatile in terms of parameter selection. We obtain this signature scheme by replacing the FFO...

Branching program (BP) is a DAG-based non-uniform computational model for L/poly class. It has been widely used in formal verification, logic synthesis, and data analysis. As a special BP, a decision tree is a popular machine learning classifier for its effectiveness and simplicity. In this work, we propose a UC-secure efficient 3-party computation platform for outsourced branching program and/or decision tree evaluation. We construct a constant-round protocol and a linear-round protocol. In...

Secure computation enables two or more parties to jointly evaluate a function without revealing to each other their private input. G-module is an abelian group M, where the group G acts compatibly with the abelian group structure on M. In this work, we present several secure computation protocols for G-module operations in the online/offline mode. We then show how to instantiate those protocols to implement many widely used secure computation primitives in privacy-preserving machine learning...

Due to their use in crypto-currencies, threshold ECDSA signatures have received much attention in recent years. Though efficient solutions now exist both for the two party, and the full threshold scenario, there is still much room for improvement, be it in terms of protocol functionality, strengthening security or further optimising efficiency. In the past few months, a range of protocols have been published, allowing for a non interactive -- and hence extremely efficient -- signing...

We define and construct Deniable Fully Homomorphic Encryption based on the Learning With Errors (LWE) polynomial hardness assumption. Deniable FHE enables storing encrypted data in the cloud to be processed securely without decryption, maintaining deniability of the encrypted data, as well the prevention of vote-buying in electronic voting schemes where encrypted votes can be tallied without decryption. Our constructions achieve compactness independently of the level of deniability- both...

A non-interactive zero-knowledge (NIZK) protocol enables a prover to convince a verifier of the truth of a statement without leaking any other information by sending a single message. The main focus of this work is on exploring short pairing-based NIZKs for all NP languages based on standard assumptions. In this regime, the seminal work of Groth, Ostrovsky, and Sahai (J.ACM'12) (GOS-NIZK) is still considered to be the state-of-the-art. Although fairly efficient, one drawback of GOS-NIZK is...

Email communication is amongst the most prominent online activities, and as such, can put sensitive information at risk. It is thus of high importance that internet email applications are designed in a privacy-aware manner and analyzed under a rigorous threat model. The Snowden revelations (2013) suggest that such a model should feature a global adversary, in light of the observational tools available. Furthermore, the fact that protecting metadata can be of equal importance as protecting...

We study the problem of securely building single-commodity multi-markets auction mechanisms. We introduce a novel greedy algorithm and its corresponding privacy preserving implementation using secure multi-party computation. More specifically, we determine the quantity of supply and demand bids maximizing welfare. Each bid is attached to a specific market, but exchanges between different markets are allowed up to some upper limit. The general goal is for the players to bid their intended...

This paper presents expressive predicate encryption (PE) systems, namely non-zero inner-product-predicate encryption (NIPPE) and attribute-based encryption (ABE) supporting monotone span programs achieving best known parameters among existing similar schemes under well-studied static complexity assumptions. Both the constructions are built in composite order bilinear group setting and involve only 2 group elements in the ciphertexts. More interestingly, our NIPPE scheme, which additionally...

We describe a highly optimized protocol for general-purpose secure two-party computation (2PC) in the presence of malicious adversaries. Our starting point is a protocol of Kolesnikov \etal (TCC 2015). We adapt that protocol to the online/offline setting, where two parties repeatedly evaluate the same function (on possibly different inputs each time) and perform as much of the computation as possible in an offline preprocessing phase before their inputs are known. Along the way we develop...

We provide a new construction of functional encryption (FE) for circuits in the bounded collusion model. In this model, security of the scheme is guaranteed as long as the number of colluding adversaries can be a-priori bounded by some polynomial q . Our construction supports arithmetic circuits as against Boolean circuits, which have been the focus of all prior work. The ciphertext of our scheme is sublinear in the circuit size for the circuit class NC_1 when based on Ring LWE and any...

Electronic Health Record (EHR) system facilitates us a lot for health record management. Privacy risk of patients' records is the dominating obstacle in the widely deployed EHRs. Role-based access control (RBAC) schemes offer an access control on EHRs according to one's role. Only the medical staff with roles satisfying the specified access policies can read EHRs. In existing schemes, attackers can link patients' identities to their doctors. Therefore, the classification of patients'...

Proofs of partial knowledge allow a prover to prove knowledge of witnesses for k out of n instances of NP languages. Cramer, Schoenmakers and Damg\aa rd [CDS94] provided an efficient construction of a 3-round public-coin witness-indistinguishable (k, n)-proof of partial knowledge for any NP language, by cleverly combining n executions of Sigma-protocols for that language. This transform assumes that all n instances are fully specified before the proof starts, and thus directly rules out the...

We introduce a setting that we call Device-Enhanced PAKE (DE-PAKE), where PAKE (password-authenticated key exchange) protocols are strengthened against online and offline attacks through the use of an auxiliary device that aids the user in the authentication process. We build such schemes and show that their security, properly formalized, achieves maximal-attainable resistance to online and offline attacks in both PKI and PKI-free settings. In particular, an online attacker must guess the...

The advent of cloud computing has given rise to a plethora of work on verifiable delegation of computation. Homomorphic signatures are powerful tools that can be tailored for verifiable computation, as long as they are efficiently verifiable. The main advantages of homomorphic signatures for verifiable computation are twofold: \begin{inparaenum}[(i)] \item Any third party can verify the correctness of the delegated computation, \item and this third party is not required to have access to...

We introduce quantitative usability and security models to guide the design of \emph{password management schemes} --- systematic strategies to help users create and remember multiple passwords. In the same way that security proofs in cryptography are based on complexity-theoretic assumptions (e.g., hardness of factoring and discrete logarithm), we quantify usability by introducing \emph{usability assumptions}. In particular, password management relies on assumptions about human memory,...

Secure 2-party computation (2PC) is becoming practical for some applications. However, most approaches are limited by the fact that the desired functionality must be represented as a boolean circuit. In response, random-access machines (RAM programs) have recently been investigated as a promising alternative representation. In this work, we present the first practical protocols for evaluating RAM programs with security against malicious adversaries. A useful efficiency measure is to divide...

Protocols for secure two-party computation enable a pair of mistrusting parties to compute a joint function of their private inputs without revealing anything but the output. One of the fundamental techniques for obtaining secure computation is that of Yao's garbled circuits. In the setting of malicious adversaries, where the corrupted party can follow any arbitrary (polynomial-time) strategy in an attempt to breach security, the cut-and-choose technique is used to ensure that the garbled...

Attribute-based encryption (ABE) is a type of public key encryption that allows users to encrypt and decrypt messages based on user attributes. For instance, one can encrypt a message to any user satisfying the boolean formula (``crypto conference attendee'' AND ``PhD student'') OR ``IACR member''. One drawback is that encryption and key generation computational costs scale with the complexity of the access policy or number of attributes. In practice, this makes encryption and user key...

Certificateless Public key Cryptography is a widely studied paradigm due to its advantages of not having the key-escrow problem and the lack of use of certificates. Online-Offline signature schemes are extremely relevant today because of their great practical applications. In an online-offline signature scheme all the heavy computation is done on powerful processors and stored securely in the offline phase, and the online component requires only light computation. Hence, it is widely used in...

Digital signature is one of the basic primitives in cryptography. A common paradigm of obtaining signatures, known as the Fiat-Shamir (FS) paradigm, is to collapse any Σ-protocol (which is 3-round public-coin honest-verifier zero-knowledge) into a non-interactive scheme with hash functions that are modeled to be random oracles (RO). The Digital Signature Standard (DSS) and Schnorr’s signature schemes are two salient examples following the FS-paradigm. In this work, we present a...

Online/Offline signcryption is a cryptographic primitive where the signcryption process is divided into two phases - online and offline phase. Most of the computations are carried out offline (where the message and the receiver identity are unavailable). The online phase does not require any heavy computations like pairing, multiplication on elliptic curves and is very efficient. To the best of our knowledge there exists three online/offline signcryption schemes in the literature : we...

In this paper, we redefine a cryptographic notion called Online/Offline Identity-Based Signcryption. It is an ``online/offline'' version of identity-based signcryption, where most of the computations are carried out offline while the online part does not require any heavy computations such as pairings or multiplications on elliptic curve. It is particularly suitable for power-constrained devices such as smart cards. We give a concrete implementation of online/offline...

An identity-based online/offline encryption (IBOOE) scheme splits the encryption process into two phases. The first phase performs most of the heavy computations, such as modular exponentiation or pairing over points on elliptic curve. The knowledge of the plaintext or the receiver's identity is not required until the second phase, where the ciphertext is produced by only light computations, such as integer addition/multiplication or hashing. This division of computations makes encryption...

Consider the situation where a low power device with limited computational power has to perform cryptographic operation in order to do secure communication to the base station where the computational power is not limited. The most obvious way is to split each and every cryptographic operations into resource consuming, heavy operations (which are performed when the device is idle) and the fast light weight operations (which are executed on the fly). This concept is called online/offline...

In this paper, we present an \emph{online/offline identity-based signature} scheme for the wireless sensor network (WSN). We argue that due to significant reduction in computational and storage costs, our scheme is particularly suitable for the WSN environment with severely constrained resources. One of the interesting features of our scheme is that it provides \textit{multi-time} usage of the offline storage, which allows the signer to re-use the offline pre-computed information in...

In this paper, we propose a new practical identity-based encryption scheme which is suitable for wireless sensor network (WSN). We call it \textit{Receiver-Bounded Online/Offline Identity-based Encryption} (RB-OOIBE). It splits the encryption process into two parts -- the offline and the online part. In the offline part, all heavy computations are done without the knowledge of the receiver's identity and the plaintext message. In the online stage, only light computations such as modular...

It has been demonstrated by Bellare, Neven, and Namprempre (Eurocrypt 2004) that identity-based signature schemes can be generically constructed from standard digital signature schemes. In this paper we consider the following natural extension: is there a generic construction of ``identity-based signature schemes with additional properties'' (such as identity-based blind signatures, verifiably encrypted signatures, ...) from standard signature schemes with the same properties? Our results...

Efficient authentication is one of important security requirements in mobile ad hoc network (MANET) routing systems. The techniques of digital signatures are generally considered as the best candidates to achieve strong authentication. However, using normal digital signature schemes is too costly to MANET due to the computation overheads. Considering the feasibility of incorporating digital signatures in MANET, we incorporate the notion of online/offline signatures, where the computational...

Common occurrence of server overload and the threat of denial-of-service (DoS) attacks makes highly desirable to improve the performance and DoS resistance of SSL handshakes. In this paper, we tackle these two related problems by proposing reverse SSL, an extension in which the server is relieved from the heavy public key decryption operation and authenticated by means of a digital signature instead. On the server side, reverse SSL employs online/offline signatures to minimize the online...

Identity-based encryption (IBE) has shown to be a useful cryptographic scheme enabling secure yet flexible role-based access control. We propose a new variant of IBE named as exclusion-intersection encryption: during encryption, the sender can specify the targeted groups that are legitimate and interested in reading the documents; there exists a trusted key generation centre generating the intersection private decryption keys on request. This special private key can only be used to decrypt...