We propose the first $\textit{distributed}$ version of a simple, efficient, and provably quantum-safe pseudorandom function (PRF). The distributed PRF (DPRF) supports arbitrary threshold access structures based on the hardness of the well-studied Learning with Rounding (LWR) problem. Our construction (abbreviated as $\mathsf{PQDPRF}$) practically outperforms not only existing constructions of DPRF based on lattice-based assumptions, but also outperforms (in terms of evaluation time) existing...

The adoption of Homomorphic Encryption (HE) and Secure Function Evaluation (SFE) applications in the real world remains lim- ited, even nearly 50 years after the introduction of HE. This is particu- larly unfortunate given the strong privacy and confidentiality guarantees these tools can offer to modern digital life. While attempting to incorporate a simple straw-man PSI protocol into a web service for matching individuals based on their profiles, we en- countered several shortcomings...

Introduced by Halevi, Ishai, Kushilevitz, and Rabin (CRYPTO 2023), Additive randomized encodings (ARE) reduce the computation of a $k$-party function $f(x_1,\dots,x_k)$ to locally computing encodings $\hat x_i$ of each input $x_i$ and then adding them together over some Abelian group into an output encoding $\hat y = \sum \hat x_i$, which reveals nothing but the result. The appeal of ARE comes from the simplicity of the non-local computation, involving only addition. This gives rise for...

Quantum key leasing, also known as public key encryption with secure key leasing (PKE-SKL), allows a user to lease a (quantum) secret key to a server for decryption purpose, with the capability of revoking the key afterwards. In the pioneering work by Chardouvelis et al (arXiv:2310.14328), a PKE-SKL scheme utilizing classical channels was successfully built upon the noisy trapdoor claw-free (NTCF) family. This approach, however, relies on the superpolynomial hardness of learning with...

We put forth and instantiate a new primitive we call simultaneous-message and succinct (SMS) secure computation. An SMS scheme enables a minimal communication pattern for secure computation in the following scenario: Alice has a large private input X, Bob has a small private input y, and Charlie wants to learn $f(X, y)$ for some public function $f$. Given a common reference string (CRS) setup phase, an SMS scheme for a function f is instantiated with two parties holding inputs $X$ and...

Distributed Point Functions (DPFs) are a useful cryptographic primitive enabling a dealer to distribute short keys to two parties, such that the keys encode additive secret shares of a secret point function. However, in many applications of DPFs, no single dealer entity has full knowledge of the secret point function, necessitating the parties to run an interactive protocol to emulate the setup. Prior works have aimed to minimize complexity metrics of such distributed setup protocols, e.g.,...

Homomorphic secret sharing (HSS) is a distributed analogue of fully homomorphic encryption (FHE) where following an input-sharing phase, two or more parties can locally compute a function over their private inputs to obtain shares of the function output. Over the last decade, HSS schemes have been constructed from an array of different assumptions. However, all existing HSS schemes, except ones based on assumptions known to imply multi-key FHE, require a public-key infrastructure (PKI) or...

Threshold fully homomorphic encryption (ThFHE) enables multiple parties to compute functions over their sensitive data without leaking data privacy. Most of existing ThFHE schemes are restricted to full threshold and require the participation of all parties to output computing results. Compared with these full-threshold schemes, arbitrary threshold (ATh)-FHE schemes are robust to non-participants and can be a promising solution to many real-world applications. However, existing AThFHE...

As Fully Homomorphic Encryption (FHE) enables computation over encrypted data, it is a natural question of how efficiently it handles standard integer computations like $64$-bit arithmetic. It has long been believed that the CGGI/DM family or the BGV/BFV family are the best options, depending on the size of the parallelism. The Cheon-Kim-Kim-Song (CKKS) scheme, although being widely used in many applications like machine learning, was not considered a good option as it is more focused on...

Fuzzy private set intersection (Fuzzy PSI) is a cryptographic protocol for privacy-preserving similarity matching, which is one of the essential operations in various real-world applications such as facial authentication, information retrieval, or recommendation systems. Despite recent advancements in fuzzy PSI protocols, still a huge barrier remains in deploying them for these applications. The main obstacle is the high dimensionality, e.g., from 128 to 512, of data; lots of existing...

This paper presents the first black-box registered ABE for circuit from lattices. The selective security is based on evasive LWE assumption [EUROCRYPT'22, CRYPTO'22]. The unique prior Reg-ABE scheme from lattices is derived from non-black-box construction based on function-binding hash and witness encryption [CRYPTO'23]. Technically, we first extend the black-box registration-based encryption from standard LWE [CRYPTO'23] so that we can register a public key with a function; this yields a...

Privacy and security have become critical priorities in many scenarios. Privacy-preserving computation (PPC) is a powerful solution that allows functions to be computed directly on encrypted data. Garbled circuit (GC) is a key PPC technology that enables secure, confidential computing. GC comes in two forms: Boolean GC supports all operations by expressing functions as logic circuits; arithmetic GC is a newer technique to efficiently compute a set of arithmetic operations like addition and...

Time-lock puzzles (TLP) are a cryptographic tool that allow one to encrypt a message into the future, for a predetermined amount of time $T$. At present, we have only two constructions with provable security: One based on the repeated squaring assumption and the other based on obfuscation. Basing TLP on any other assumption is a long-standing question, further motivated by the fact that known constructions are broken by quantum algorithms. In this work, we propose a new approach to...

Fully Homomorphic Encryption (FHE) allows a server to perform computations directly over the encrypted data. In general FHE protocols, the client is tasked with decrypting the computation result using its secret key. However, certain FHE applications benefit from the server knowing this result, especially without the aid of the client. Providing the server with the secret key allows it to decrypt all the data, including the client's private input. Protocols such as Goldwasser et. al....

Functional Encryption is a powerful cryptographic primitive that allows for fine-grained access control over encrypted data. In the multi-user setting, especially Multi-Client and Multi-Input, a plethora of works have been proposed to study on concrete function classes, improving security, and more. However, the CCA-security for such schemes is still an open problem, where the only known works are on Public-Key Single-Client FE ($\mathit{e.g.}$ Benhamouda, Bourse, and Lipmaa, PKC'17). ...

Multi-input and large-precision lookup table (LUT) evaluation pose significant challenges in Fully Homomorphic Encryption (FHE). Currently, two modes are employed to address this issue. One is tree-based functional bootstrapping (TFBS), which uses multiple blind rotations to construct a tree for LUT evaluation. The second is circuit bootstrapping, which decomposes all inputs into bits and utilizes a CMux tree for LUT evaluation. In this work, we propose a novel mode that is leveled...

Shadow is a family of lightweight block ciphers introduced by Guo, Li, and Liu in 2021, with Shadow-32 having a 32-bit block size and a 64-bit key, and Shadow-64 having a 64-bit block size and a 128-bit key. Both variants use a generalized Feistel network with four branches, incorporating the AND-Rotation-XOR operation similar to the Simon family for their bridging function. This paper reveals that the security claims of the Shadow family are not as strong as suggested. We present a key...

A universal thresholdizer (UT), constructed from a threshold fully homomorphic encryption by Boneh et. al , Crypto 2018, is a general framework for universally thresholdizing many cryptographic schemes. However, their framework is insufficient to construct strongly secure threshold schemes, such as threshold signatures and threshold public-key encryption, etc. In this paper, we strengthen the security definition for a universal thresholdizer and propose a scheme which satisfies our...

A garbling scheme transforms a program (e.g., circuit) $C$ into a garbled program $\hat{C}$, along with a pair of short keys $(k_{i,0},k_{i,1})$ for each input bit $x_i$, such that $(C,\hat{C}, \{k_{i,x_i}\})$ can be used to recover the output $z = C(x)$ while revealing nothing else about the input $x$. This can be naturally generalized to partial garbling, where part of the input is public, and a computation $z = C(x, y)$ is decomposed into a public part $C_{\text{pub}}(x)$, depending only...

The design of tweakable wide block ciphers has advanced significantly over the past two decades. This evolution began with the approach of designing a wide block cipher by Naor and Reingold. Since then, numerous tweakable wide block ciphers have been proposed, many of which build on existing block ciphers and are secure up to the birthday bound for the total number of blocks queried. Although there has been a slowdown in the development of tweakable wide block cipher modes in last couple of...

Multi-input functional encryption is a primitive that allows for the evaluation of an $\ell$-ary function over multiple ciphertexts, without learning any information about the underlying plaintexts. This type of computation is useful in many cases where one has to compute over encrypted data, such as privacy-preserving cloud services, federated learning, or more generally delegation of computation from multiple clients. It has recently been shown by Alborch et al. in PETS '24 to be useful to...

We present the first public and in-depth cryptanalysis of TEA-3, a stream cipher used in TETRA radio networks that was kept secret until recently. While the same also holds for the six other TETRA encryption algorithms, we pick TEA-3 to start with as (i) it is not obviously weakened as TEA-{1,4,7} but (ii) in contrast to TEA-2 it is approved only for extra-European emergency service, and (iii) as already noted by [MBW23] the TEA-3 design surprisingly contains a non-bijective S-box. Most...

Fully Homomorphic Encryption (FHE) enables secure computation of functions on ciphertexts without requiring decryption. Specifically, AP-like HE schemes exploit an intrinsic bootstrapping method called blind rotation. In blind rotation, a look-up table is homomorphically evaluated on the input ciphertext through the iterative multiplication of monomials. However, the algebraic structure of the multiplicative group of monomials imposes certain limitations on the input and output plaintext...

Private set intersection (PSI) allows any two parties (say client and server) to jointly compute the intersection of their sets without revealing anything else. Fully homomorphic encryption (FHE)-based PSI is a cryptographic solution to implement PSI-based protocols. Most FHE-based PSI protocols implement hash function approach and oblivious transfer approach. The main limitations of their protocols are 1) high communication complexity, that is, $O(xlogy)$ (where $x$ is total number of...

We give new constructions of succinct non-interactive arguments ($\mathsf{SNARG}$s) for $\mathsf{NP}$ in the settings of both non-adaptive and adaptive soundness. Our construction of non-adaptive $\mathsf{SNARG}$ is universal assuming the security of a (leveled or unleveled) fully homomorphic encryption ($\mathsf{FHE}$) scheme as well as a batch argument ($\mathsf{BARG}$) scheme. Specifically, for any choice of parameters $\ell$ and $L$, we construct a candidate $\mathsf{SNARG}$ scheme...

Group signature (GS) is a well-known cryptographic primitive providing anonymity and traceability. Several implication results have been given by mainly focusing on the several security levels of anonymity, e.g., fully anonymous GS implies public key encryption (PKE) and selfless anonymous GS can be constructed from one-way functions and non-interactive zero knowledge poofs, and so on. In this paper, we explore an winning condition of full traceability: an adversary is required to produce a...

As dataset sizes grow, users increasingly rely on encrypted data and secure range queries on cloud servers, raising privacy concerns about potential data leakage. Order-revealing encryption (ORE) enables efficient operations on numerical datasets, and Delegatable ORE (DORE) extends this functionality to multi-client environments, but it faces risks of token forgery. Secure DORE (SEDORE) and Efficient DORE (EDORE) address some vulnerabilities, with EDORE improving speed and storage...

A message authentication code (MAC) is a symmetric-key cryptographic function used to authenticate a message by assigning it a tag. This tag is a short string that is difficult to reproduce without knowing the key. The tag ensures both the authenticity and integrity of the message, enabling the detection of any modifications. A significant number of existing message authentication codes (MACs) are based on block ciphers (BCs) and tweakable block ciphers (TBCs). These MACs offer various...

Proxy re-encryption (PRE) allows a semi-honest party (called a proxy) to convert ciphertexts under a public key into ciphertexts under another public key. Due to this functionality, there are various applications such as encrypted email forwarding, key escrow, and secure distributed file systems. On the other hand, post-quantum cryptography (PQC) is one of the most important research areas. However, there is no post-quantum PRE scheme with security against adaptive chosen ciphertext attacks...

Private Set Intersection (PSI) is a cryptographic primitive that allows two parties to obtain the intersection of their private input sets while revealing nothing more than the intersection. PSI and its numerous variants, which compute on the intersection of items and their associated weights, have been widely studied. In this paper, we revisit the problem of finding the best item in the intersection according to weight sum introduced by Beauregard et al. (SCN '22), which is a special...

The Ascon authenticated encryption scheme and hash function of Dobraunig et al (Journal of Cryptology 2021) were recently selected as winner of the NIST lightweight cryptography competition. The mode underlying Ascon authenticated encryption (Ascon-AE) resembles ideas of SpongeWrap, but not quite, and various works have investigated the generic security of Ascon-AE, all covering different attack scenarios and with different bounds. This work systemizes knowledge on the mode security of...

In this paper, we put forward a new practical application of Inner-Product Functional Encryption (IPFE) that we call Message Selection functional encryption (M-Sel) which allows users to decrypt selected portions of a ciphertext. In a message selection functional encryption scheme, the plaintext is partitioned into a set of messages M = {m1, . . . , mt}. The encryption of M consists in encrypting each of its elements using distinct encryption keys. A user with a functional decryption key skx...

Recently, Francati et al. (Asiacrypt 2023) provided the first registered functional encryption (Reg-FE) beyond predicates. Reg-FE addresses the key escrow problem in functional encryption by allowing users to generate their own key pairs, effectively replacing the traditional private-key generator with a key curator. The key curator holds no secret information and runs deterministic algorithms to generate master public key for encryption and helper keys for decryption. However, existing...

We present a novel protocol for two-party ECDSA that achieves two rounds (a single back-and-forth communication) at the cost of a single oblivious linear function evaluation (OLE). In comparison, the previous work of [DKLs18] (S&P 2018) achieves two rounds at the cost of three OLEs, while [BHL24] (Manuscript 2024) requires expensive zero-knowledge proofs on top of the OLE. We demonstrate this by proving that in the generic group model, any adversary capable of generating forgeries for our...

Multi-input Attribute-Based Encryption (ABE) is a generalization of key-policy ABE where attributes can be independently encrypted across several ciphertexts, and a joint decryption of these ciphertexts is possible if and only if the combination of attributes satisfies the policy of the decryption key. We extend this model by introducing a new primitive that we call Multi-Client ABE (MC-ABE), which provides the usual enhancements of multi-client functional encryption over multi-input...

Key Transparency (KT) systems have emerged as a critical technology for securely distributing and verifying the correctness of public keys used in end-to-end encrypted messaging services. Despite substantial academic interest, increased industry adoption, and IETF standardization efforts, KT systems lack a holistic and formalized security model, limiting their resilience to practical threats and constraining future development. In this paper, we introduce the first cryptographically sound...

In this paper we present RevoLUT, a library implemented in Rust that reimagines the use of Look-Up-Tables (LUT) beyond their conventional role in function encoding, as commonly used in TFHE's programmable boostrapping. Instead, RevoLUT leverages LUTs as first class objects, enabling efficient oblivious operations such as array access, elements sorting and permutation directly within the table. This approach supports oblivious algortithm, providing a secure, privacy-preserving solution for...

We consider a generalization of the Learning With Error problem, referred to as the white-box learning problem: You are given the code of a sampler that with high probability produces samples of the form $y,f(y)+\epsilon$ where is small, and $f$ is computable in polynomial-size, and the computational task consist of outputting a polynomial-size circuit $C$ that with probability, say, $1/3$ over a new sample $y$? according to the same distributions, approximates $f(y)$ (i.e., $|C(y)-f(y)$ ...

Authenticated encryption schemes guarantee that parties who share a secret key can communicate confidentially and authentically. One of the most popular and widely used authenticated encryption schemes is GCM by McGrew and Viega (INDOCRYPT 2004). However, despite its simplicity and efficiency, GCM also comes with its deficiencies, most notably devastating insecurity against nonce-misuse and imperfect security for short tags. Very recently, Campagna, Maximov, and Mattsson presented GCM-SST...

The password-hardening service (PH) is a crypto service that armors canonical password authentication with an external key against offline password guessing in case the password file is somehow compromised/leaked. The game-based formal treatment of PH was brought by Everspaugh et al. at USENIX Security'15. Their work is followed by efficiency-enhancing PO-COM (CCS'16), security-patching Phoenix (USENIX Security'17), and functionality-refining PW-Hero (SRDS'22). However, the issue of single...

As language models are increasingly deployed in cloud environments, privacy concerns have become a significant issue. To address this, we design THOR, a secure inference framework for transformer models on encrypted data. Specifically, we first propose new fast matrix multiplication algorithms based on diagonal-major order encoding and extend them to parallel matrix computation through the compact ciphertext packing technique. Second, we design efficient protocols for secure computations of...

We initiate the study of the black-box complexity of private-key functional encryption (FE). Of central importance in the private-key setting is the inner-product functionality, which is currently only known from assumptions that imply public-key encryption, such as Decisional Diffie-Hellman or Learning-with-Errors. As our main result, we rule out black-box constructions of private-key inner-product FE from random oracles. This implies a black-box separation between private-key...

Given the devastating security compromises caused by side-channel attacks on existing classical systems, can we store our private data encoded as a quantum state so that they can be kept private in the face of arbitrary side-channel attacks? The unclonable nature of quantum information allows us to build various quantum protection schemes for cryptographic information such as secret keys. Examples of quantum protection notions include copy-protection, secure leasing, and finally,...

Perceptual hash functions map multimedia content that is perceptually close to outputs strings that are identical or similar. They are widely used for the identification of protected copyright and illegal content in information sharing services: a list of undesirable files is hashed with a perceptual hash function and compared, server side, to the hash of the content that is uploaded. Unlike cryptographic hash functions, the design details of perceptual hash functions are typically kept...

As privacy concerns have arisen in machine learning, privacy-preserving machine learning (PPML) has received significant attention. Fully homomorphic encryption (FHE) and secure multi-party computation (MPC) are representative building blocks for PPML. However, in PPML protocols based on FHE and MPC, interaction between the client (who provides encrypted input data) and the evaluator (who performs the computation) is essential to obtain the final result in plaintext. Functional encryption...

We extend the concept of access control for functional encryption, introduced by Abdalla et al. (ASIACRYPT 2020), to function-revealing encryption (Joy and Passelègue, SCN 2018). Here “access control” means that function evaluation is only possible when a specified access policy is met. Specifically, we introduce access-controlled inner product function-revealing encryption (AC-IPFRE) and give two applications. On the theoretical side, we use AC-IPFRE to show that function-hiding...

Protein sequence classification is crucial in many research areas, such as predicting protein structures and discovering new protein functions. Leveraging large language models (LLMs) is greatly promising to enhance our ability to tackle protein sequence classification problems; however, the accompanying privacy issues are becoming increasingly prominent. In this paper, we present a privacy-preserving, non-interactive, efficient, and accurate protocol called encrypted DASHformer to evaluate...

Pseudorandom codes are error-correcting codes with the property that no efficient adversary can distinguish encodings from uniformly random strings. They were recently introduced by Christ and Gunn [CRYPTO 2024] for the purpose of watermarking the outputs of randomized algorithms, such as generative AI models. Several constructions of pseudorandom codes have since been proposed, but none of them are robust to error channels that depend on previously seen codewords. This stronger kind of...

We present a new construction of two-party, threshold ECDSA, building on a 2017 scheme of Lindell and improving his scheme in several ways. ECDSA signing is notoriously hard to distribute securely, due to non-linearities in the signing function. Lindell's scheme uses Paillier encryption to encrypt one party's key share and handle these non-linearities homomorphically, while elegantly avoiding any expensive zero knowledge proofs over the Paillier group during the signing process. However,...

A recent work of Kalai et al. (STOC 2023) shows how to compile any multi-player nonlocal game into a protocol with a single computationally-bounded prover. Subsequent works have built on this to develop new cryptographic protocols, where a completely classical client can verify the validity of quantum computation done by a quantum server. Their compiler relies on the existence of quantum fully-homomorphic encryption. In this work, we propose a new compiler for transforming nonlocal games...

We put forth Oblivious State Preparation (OSP) as a cryptographic primitive that unifies techniques developed in the context of a quantum server interacting with a classical client. OSP allows a classical polynomial-time sender to input a choice of one out of two public observables, and a quantum polynomial-time receiver to recover an eigenstate of the corresponding observable -- while keeping the sender's choice hidden from any malicious receiver. We obtain the following results: - The...

Succinct randomized encodings allow encoding the input $x$ of a time-$t$ uniform computation $M(x)$ in sub-linear time $o(t)$. The resulting encoding $\tilde{x}$ allows recovering the result of the computation $M(x)$, but hides any other information about $x$. These encodings have powerful applications, including time-lock puzzles, reducing communication in MPC, and bootstrapping advanced encryption schemes. Until not long ago, the only known constructions were based on...

Pseudo-Random Injections (PRIs) have been used in several applications in symmetric-key cryptography, such as in the idealization of Authenticated Encryption with Associated Data (AEAD) schemes, building robust AEAD, and, recently, in converting a committing AEAD scheme into a succinctly committing AEAD scheme. In Crypto 2024, Bellare and Hoang showed that if an AEAD scheme is already committing, it can be transformed into a succinctly committing scheme by encrypting part of the plaintext...

Recent active studies have demonstrated that cryptography without one-way functions (OWFs) could be possible in the quantum world. Many fundamental primitives that are natural quantum analogs of OWFs or pseudorandom generators (PRGs) have been introduced, and their mutual relations and applications have been studied. Among them, pseudorandom function-like state generators (PRFSGs) [Ananth, Qian, and Yuen, Crypto 2022] are one of the most important primitives. PRFSGs are a natural quantum...

The enormous potential of Attribute-Based Encryption (ABE) in the context of IoT has driven researchers to propose pairing-free ABE schemes that are suitable for resource-constrained devices. Unfortunately, many of these schemes turned out to be insecure. This fact seems to reinforce the point of view of some authors according to which instantiating an Identity-Based Encryption (IBE) in plain Decision Diffie-Hellman (DDH) groups is impossible. In this paper, we provide a generic AND gate...

We introduce the notion of pseudorandom obfuscation (PRO), a way to obfuscate (keyed) pseudorandom functions $f_K$ in an average-case sense. We introduce several variants of pseudorandom obfuscation and show constructions and applications. For some of our applications that can be achieved using full-fledged indistinguishability obfuscation (iO), we show constructions using lattice-based assumptions alone; the other applications we enable using PRO are simply not known even assuming iO. We...

We construct the first multi-input functional encryption (MIFE) and indistinguishability obfuscation (iO) schemes for pseudorandom functionalities, where the output of the functionality is pseudorandom for every input seen by the adversary. Our MIFE scheme relies on LWE and evasive LWE (Wee, Eurocrypt 2022 and Tsabary, Crypto 2022) for constant arity functions, and a strengthening of evasive LWE for polynomial arity. Thus, we obtain the first MIFE and iO schemes for a nontrivial...

We provide the first construction of compact Functional Encryption (FE) for pseudorandom functionalities from the evasive LWE and LWE assumptions. Intuitively, a pseudorandom functionality means that the output of the circuit is indistinguishable from uniform for every input seen by the adversary. This yields the first compact FE for a nontrivial class of functions which does not rely on pairings. We demonstrate the power of our new tool by using it to achieve optimal parameters for both...

We present an asynchronous secure multi-party computation (MPC) protocol that is practically efficient. Our protocol can evaluate any arithmetic circuit with linear communication in the number of parties per multiplication gate, while relying solely on computationally lightweight cryptography such as hash function and symmetric encryption. Our protocol is optimally resilient and tolerates $t$ malicious parties among $n = 3t+1$ parties. At the technical level, we manage to apply the...

Non-interactive zero-knowledge proofs (NIZK) are essential building blocks in threshold cryptosystems like multiparty signatures, distributed key generation, and verifiable secret sharing, allowing parties to prove correct behavior without revealing secrets. Furthermore, universally composable (UC) NIZKs enable seamless composition in the larger cryptosystems. A popular way to construct NIZKs is to compile interactive protocols using the Fiat-Shamir transform. Unfortunately, Fiat-Shamir...

In a functional encryption (FE) scheme, a user that holds a ciphertext and a function-key can learn the result of applying the function to the plaintext message. Security requires that the user does not learn anything beyond the function evaluation. On the other hand, unclonable encryption (UE) is a uniquely quantum primitive, which ensures that an adversary cannot duplicate a ciphertext to decrypt the same message multiple times. In this work we introduce unclonable quantum...

Bootstrapping is the core task in fully homomorphic encryption. It is designed to self-clean encrypted data to support unlimited level of homomorphic computing. FHEW/TFHE cryptosystem provides the fastest bootstrapping machinery in addition to the unique homomorphic evaluation functionality. In 2021, the problem of large-precision bootstrapping was investigated in the literature, with fast algorithms proposed and implemented. A common strategy to all the algorithms is to decompose the...

Homomorphic Encryption (HE) enables operations on encrypted data without requiring decryption, thus allowing for secure handling of confidential data within smart contracts. Among the known HE schemes, FHEW and TFHE are particularly notable for use in smart contracts due to their lightweight nature and support for arbitrary logical gates. In contrast, other HE schemes often require several gigabytes of keys and are limited to supporting only addition and multiplication. As a result, there...

Software watermarking allows for embedding a mark into a piece of code, such that any attempt to remove the mark will render the code useless. Provably secure watermarking schemes currently seems limited to programs computing various cryptographic operations, such as evaluating pseudorandom functions (PRFs), signing messages, or decrypting ciphertexts (the latter often going by the name ``traitor tracing''). Moreover, each of these watermarking schemes has an ad-hoc construction of its...

Collision-resistant hashing (CRH) is a cornerstone of cryptographic protocols. However, despite decades of research, no construction of a CRH based solely on one-way functions has been found. Moreover, there are black-box limitations that separate these two primitives. Harnik and Naor [HN10] overcame this black-box barrier by introducing the notion of instance compression. Instance compression reduces large NP instances to a size that depends on their witness size while preserving the...

Top trading cycles (TTC) is a famous algorithm for trading indivisible goods between a set of agents such that all agents are as happy as possible about the outcome. In this paper, we present a protocol for executing TTC in a privacy preserving way. To the best of our knowledge, it is the first of its kind. As a technical contribution of independent interest, we suggest a new algorithm for determining all nodes in a functional graph that are on a cycle. The algorithm is particularly well...

This article discusses fully homomorphic encryption and homomorphic sorting. Homomorphic encryption is a special encryption technique that allows all kinds of operations to be performed on ciphertext, and the result is still decryptable, such that when decrypted, the result is the same as that obtained by performing the same operation on the plaintext. Homomorphic sorting is an important problem in homomorphic encryption. Currently, there has been a volume of work on homomorphic sorting. In...

Quantum pseudorandomness has found applications in many areas of quantum information, ranging from entanglement theory, to models of scrambling phenomena in chaotic quantum systems, and, more recently, in the foundations of quantum cryptography. Kretschmer (TQC '21) showed that both pseudorandom states and pseudorandom unitaries exist even in a world without classical one-way functions. To this day, however, all known constructions require classical cryptographic building blocks which are...

The Cheon-Kim-Kim-Song (CKKS) scheme is renowned for its efficiency in encrypted computing over real numbers. However, it lacks an important functionality that most exact schemes have, an efficient modular reduction. This derives from the fundamental difference in encoding structure. The CKKS scheme encodes messages to the least significant bits, while the other schemes encode to the most significant bits (or in an equivalent manner). As a result, CKKS could enjoy an efficient rescaling but...

The native plaintexts of the Cheon-Kim-Kim-Song (CKKS) fully homomorphic encryption scheme are vectors of approximations to complex numbers. Drucker et al. [J. Cryptol.'24] have showed how to use CKKS to efficiently perform computations on bits and small bit-length integers, by relying on their canonical embeddings into the complex plane. For small bit-length integers, Chung et al. [IACR eprint'24] recently suggested to rather rely on an embedding into complex roots of unity, to gain...

Searchable encryption is a cryptographic primitive that allows us to perform searches on encrypted data. Searchable encryption schemes require that ciphertexts do not leak information about keywords. However, most of the existing schemes do not achieve the security notion that trapdoors do not leak information. Shen et al. (TCC 2009) proposed a security notion called full security, which includes both ciphertext privacy and trapdoor privacy, but there are few fully secure constructions. Full...

A hybrid cryptosystem combines two systems that fulfill the same cryptographic functionality, and its security enjoys the security of the harder one. There are many proposals for hybrid public-key encryption (hybrid PKE), hybrid signature (hybrid SIG) and hybrid authenticated key exchange (hybrid AKE). In this paper, we fill the blank of Hybrid Password Authentication Key Exchange (hybrid PAKE). For constructing hybrid PAKE, we first define an important class of PAKE -- full DH-type...

The Ducas-Micciancio (DM/FHEW) and Chilotti-Gama-Georgieva-Izabachène (CGGI/TFHE) cryptosystems provide a general privacy-preserving computation capability. These fully homomorphic encryption (FHE) cryptosystems can evaluate an arbitrary function expressed as a general look-up table (LUT) via the method of functional bootstrapping (also known as programmable bootstrapping). The main limitation of DM/CGGI functional bootstrapping is its efficiency because this procedure has to bootstrap every...

Authenticated encryption (AE) is a cryptographic mechanism that allows communicating parties to protect the confidentiality and integrity of messages exchanged over a public channel, provided they share a secret key. In this work, we present new AE schemes leveraging the SHA-3 standard functions SHAKE128 and SHAKE256, offering 128 and 256 bits of security strength, respectively, and their “Turbo” counterparts. They support session-based communication, where a ciphertext authenticates the...

Artificial Intelligence (AI) has steadily improved across a wide range of tasks, and a significant breakthrough towards general intelligence was achieved with the rise of generative deep models, which have garnered worldwide attention. However, the development and deployment of AI are almost entirely controlled by a few powerful organizations and individuals who are racing to create Artificial General Intelligence (AGI). These centralized entities make decisions with little public oversight,...

As an emerging primitive, Registered Functional Encryption (RFE) eliminates the key-escrow issue that threatens numerous works for functional encryption, by replacing the trusted authority with a transparent key curator and allowing each user to sample their decryption keys locally. In this work, we present a new black-box approach to construct RFE for all polynomial-sized circuits. It considers adaptive simulation-based security in the bounded collusion model (Gorbunov et al. - CRYPTO'12),...

Secure key leasing (a.k.a. key-revocable cryptography) enables us to lease a cryptographic key as a quantum state in such a way that the key can be later revoked in a verifiable manner. We propose a simple framework for constructing cryptographic primitives with secure key leasing via the certified deletion property of BB84 states. Based on our framework, we obtain the following schemes. - A public key encryption scheme with secure key leasing that has classical revocation based on any...

Searchable encryption, or more generally, structured encryption, permits search over encrypted data. It is an important cryptographic tool for securing cloud storage. The standard security notion for structured encryption mandates that a protocol leaks nothing about the data or queries, except for some allowed leakage, defined by the leakage function. This is due to the fact that some leakage is unavoidable for efficient schemes. Unfortunately, it was shown by numerous works that even...

Tweakable enciphering modes (TEMs) provide security in a variety of storage and space-critical applications like disk and file-based encryption, and packet-based communication protocols, among others. XCB-AES (known as XCBv2) is specified in the IEEE 1619.2 standard for encryption of sector-oriented storage media and it comes with a proof of security for block-aligned input messages. In this work, we demonstrate the $\textit{first}$ and most efficient plaintext recovery attack on...

The traditional definition of fully homomorphic encryption (FHE) is not composable, i.e., it does not guarantee that evaluating two (or more) homomorphic computations in a sequence produces correct results. We formally define and investigate a stronger notion of homomorphic encryption which we call "fully composable homomorphic encryption", or "composable FHE". The definition is both simple and powerful: it does not directly involve the evaluation of multiple functions, and yet it...

State-of-the-art database implementations offer a wide range of functionalities and impressive performances while supporting highly concurrent loads. However they all rely on the server knowing the content of the database, which raises issues when sensitive information is being stored on a server that cannot be trusted. Encrypting documents before sending them to a remote server solves the confidentiality issue at the cost of loosing the keyword search functionality. Cryptographic primitives...

In classical cryptography, one-way functions (OWFs) are the minimal assumption, while recent active studies have demonstrated that OWFs are not necessarily the minimum assumption in quantum cryptography. Several new primitives have been introduced such as pseudorandom unitaries (PRUs), pseudorandom function-like state generators (PRFSGs), pseudorandom state generators (PRSGs), one-way state generators (OWSGs), one-way puzzles (OWPuzzs), and EFI pairs. They are believed to be weaker than...

In this paper, we introduce the notion of relaxed lattice-based programmable hash function (RPHF), which is a novel variant of lattice-based programmable hash functions (PHFs). Lattice-based PHFs, together with preimage trapdoor functions (TDFs), have been widely utilized (implicitly or explicitly) in the construction of adaptively secure identity-based encryption (IBE) schemes. The preimage length and the output length of the underlying PHF and TDF together determine the user secret key and...

In decentralized finance (DeFi), the public availability of pending transactions presents significant privacy concerns, enabling market manipulation through miner extractable value (MEV). MEV occurs when block proposers exploit the ability to reorder, omit, or include transactions, causing financial loss to users from frontrunning. Recent research has focused on encrypting pending transactions, hiding transaction data until block finalization. To this end, Choudhuri et al. (USENIX '24)...

XCB, a tweakable enciphering mode, is part of IEEE Std. 1619.2 for shared storage media. We show that all versions of XCB are not secure through three plaintext recovery attacks. A key observation is that XCB behaves like an LRW1-type tweakable block cipher for single-block messages, which lacks CCA security. The first attack targets one-block XCB, using three queries to recover the plaintext. The second one requires four queries to recover the plaintext that excludes one block. The last one...

In scenarios where a seller holds sensitive data $x$, like employee / patient records or ecological data, and a buyer seeks to obtain an evaluation of specific function $f$ on this data, solutions in trustless digital environments like blockchain-based Web3 systems typically fall into two categories: (1) Smart contract-powered solutions and (2) cryptographic solutions leveraging tools such as adaptor signatures. The former approach offers atomic transactions where the buyer learns the...

Homomorphic encryption has long been used to build voting schemes. Additively homomorphic encryption only allows simple count- ing functions. Lattice-based fully (or somewhat) homomorphic encryp- tion allows more general counting functions, but the required parameters quickly become impractical if used naively. It is safe to leak information during the counting function evaluation, as long as the information could be derived from the public result. To exploit this observation, we...

Attribute-based encryption (ABE) enables fine-grained control over which ciphertexts various users can decrypt. A master authority can create secret keys $sk_f$ with different functions (circuits) $f$ for different users. Anybody can encrypt a message under some attribute $x$ so that only recipients with a key $sk_f$ for a function such that $f(x)=1$ will be able to decrypt. There are a number of different approaches toward achieving selectively secure ABE, where the adversary has to decide...

Searchable Symmetric Encryption (SSE) has emerged as a promising tool for facilitating efficient query processing over encrypted data stored in un-trusted cloud servers. Several techniques have been adopted to enhance the efficiency and security of SSE schemes. The query processing costs, storage costs and communication costs of any SSE are directly related to the size of the encrypted index that is stored in the server. To our knowledge, there is no work directed towards minimizing the...

One of the most popular techniques to prove adaptive security of identity-based encryptions (IBE) and verifiable random functions (VRF) is the partitioning technique. Currently, there are only two methods to relate the adversary's advantage and runtime $(\epsilon, {\sf T})$ to those of the reduction's ($\epsilon_{\sf proof}, {\sf T}_{\sf proof}$) using this technique: One originates to Waters (Eurocrypt 2005) who introduced the famous artificial abort step to prove his IBE, achieving...

We present a tweakable wide block cipher called Mystrium and show it as the fastest such primitive on low-end processors that lack dedicated AES or other cryptographic instructions, such as ARM Cortex-A7. Mystrium is based on the provably secure double-decker mode, that requires a doubly extendable cryptographic keyed (deck) function and a universal hash function. We build a new deck function called Xymmer that for its compression part uses Multimixer-128, the fastest universal hash for...

We consider the graph-theoretic problem of removing (few) nodes from a directed acyclic graph in order to reduce its depth. While this problem is intractable in the general case, we provide a variety of algorithms in the case where the graph is that of a circuit of fan-in (at most) two, and explore applications of these algorithms to secure multiparty computation with low communication. Over the past few years, a paradigm for low-communication secure multiparty computation has found success...

Modern data analytics requires computing functions on streams of data points from many users that are challenging to calculate, due to both the high scale and nontrivial nature of the computation at hand. The need for data privacy complicates this matter further, as general-purpose privacy-enhancing technologies face limitations in at least scalability or utility. Existing work has attempted to improve this by designing purpose-built protocols for the use case of Private Stream Aggregation;...

Monchi is a new protocol aimed at privacy-preserving biometric identification. It begins with scores computation in the encrypted domain thanks to homomorphic encryption and ends with comparisons of these scores to a given threshold with function secret sharing. We here study the integration in that context of scores computation techniques recently introduced by Bassit et al. that eliminate homomorphic multiplications by replacing them by lookup tables. First, we extend this lookup tables...

We propose an efficient non-interactive privacy-preserving Transformer inference architecture called Powerformer. Since softmax is a non-algebraic operation, previous studies have attempted to modify it to be HE-friendly, but these methods have encountered issues with accuracy degradation or prolonged execution times due to the use of multiple bootstrappings. We propose replacing softmax with a new ReLU-based function called the \textit{Batch Rectifier-Power max} (BRPmax) function without...

We present new lattice-based attribute-based encryption (ABE) and laconic function evaluation (LFE) schemes for circuits with *sublinear* ciphertext overhead. For depth $d$ circuits over $\ell$-bit inputs, we obtain * an ABE with ciphertext and secret key size $O(1)$; * a LFE with ciphertext size $\ell + O(1)$ and digest size $O(1)$; * an ABE with public key and ciphertext size $O(\ell^{2/3})$ and secret key size $O(1)$, where $O(\cdot)$ hides $\mbox{poly}(d,\lambda)$...

Functional Encryption (FE) is a cryptographic technique established to guarantee data privacy while allowing the retrieval of specific results from the data. While traditional decryption methods rely on a secret key disclosing all the data, FE introduces a more subtle approach. The key generation algorithm generates function-specific decryption keys that can be adaptively provided based on policies. Adaptive access control is a good feature for privacy-preserving techniques. Generic schemes...

An ongoing research challenge in symmetric cryptography is to design an authenticated encryption (AE) with a commitment to the secret key or preferably to the entire context. One way to achieve this is to use a transform on an existing AE scheme, if possible with no output length expansion. At EUROCRYPT'22, Bellare and Hoang proposed the HtE transform, which lifts key-commitment to context-commitment. In the same year at ESORICS'22, Chan and Rogaway proposed the CTX transform, which works on...

In this paper, we study the security definitions of various threshold symmetric primitives. Namely, we analyze the security definitions for threshold pseudorandom functions, threshold message authentication codes and threshold symmetric encryption. In each case, we strengthen the existing security definition, and we present a scheme that satisfies our stronger notion of security. In particular, we propose indifferentiability definition and IND-CCA2 definition for a threshold pseudorandom...

Fully homomorphic encryption schemes are methods to perform compu- tations over encrypted data. Since its introduction by Gentry, there has been a plethora of research optimizing the originally inefficient cryptosystems. Over time, different families have emerged. On the one hand, schemes such as BGV, BFV, or CKKS excel at performing coefficient-wise addition or multiplication over vectors of encrypted data. In contrast, accumulator-based schemes such as FHEW and TFHE provide efficient...