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 the post-quantum migration of TLS 1.3, an ephemeral Diffie-Hellman must be replaced with a post-quantum key encapsulation mechanism (KEM). At EUROCRYPT 2022, Huguenin-Dumittan and Vaudenay [EC:HugVau22] demonstrated that KEMs with standard CPA security are sufficient for the security of the TLS1.3 handshake. However, their result is only proven in the random oracle model (ROM), and as the authors comment, their reduction is very much non-tight and not sufficient to guarantee security in...

Always Encrypted (AE) is a Microsoft SQL Server feature that allows clients to encrypt sensitive data inside client applications and ensures that the sensitive data is hidden from untrusted servers and database administrators. AE offers two column-encryption options: deterministic encryption (DET) and randomized encryption (RND). In this paper, we explore the security implications of using AE with both DET and RND encryption modes by running Leakage Abuse Attacks (LAAs) against the system....

Cryptographic wallets are an essential tool in Blockchain networks to ensure the secure storage and maintenance of an user's cryptographic keys. Broadly, wallets can be divided into three categories, namely custodial, non-custodial, and shared-custodial wallets. The first two are centralized solutions, i.e., the wallet is operated by a single entity, which inherently introduces a single point of failure. Shared-custodial wallets, on the other hand, are maintained by two independent parties,...

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

The Learning with Errors problem (LWE) and its variants are among the most popular assumptions underlying lattice-based cryptography. The Learning with Rounding problem (LWR) can be thought of as a deterministic variant of LWE. While lattice-based cryptography is known to enable many advanced constructions, constructing Fully Homomorphic Encryption schemes based on LWR remains an under-explored part of the literature. In this work, we present a thorough study of Somewhat Homomorphic...

We construct a succinct non-interactive argument (SNARG) system for every NP language $\mathcal{L}$ that has a propositional proof of non-membership for each $x\notin \mathcal{L}$. The soundness of our SNARG system relies on the hardness of the learning with errors (LWE) problem. The common reference string (CRS) in our construction grows with the space required to verify the propositional proof, and the size of the proof grows poly-logarithmically in the length of the propositional...

We present a general framework for constructing attribute-based encryption (ABE) schemes for arbitrary function class based on lattices from two ingredients, i) a noisy linear secret sharing scheme for the class and ii) a new type of inner-product functional encryption (IPFE) scheme, termed *evasive* IPFE, which we introduce in this work. We propose lattice-based evasive IPFE schemes and establish their security under simple conditions based on variants of evasive learning with errors (LWE)...

Verifiable random functions (VRFs) are pseudorandom functions with the addition that the function owner can prove that a generated output is correct (i.e., generated correctly relative to a committed key). In this paper we introduce the notion of an exponent-VRF (eVRF): a VRF that does not provide its output $y$ explicitly, but instead provides $Y = y \cdot G$, where $G$ is a generator of some finite cyclic group (or $Y=g^y$ in multiplicative notation). We construct eVRFs from DDH and from...

We build a concretely efficient threshold encryption scheme where the joint public key of a set of parties is computed as a deterministic function of their locally computed public keys, enabling a silent setup phase. By eliminating interaction from the setup phase, our scheme immediately enjoys several highly desirable features such as asynchronous setup, multiverse support, and dynamic threshold. Prior to our work, the only known constructions of threshold encryption with silent setup...

Universal computational extractors (UCEs), introduced by Bellare, Hoang, and Keelveedhi [BHK13], can securely replace random oracles in various applications, including KDM-secure encryption, deterministic encryption, RSA-OAEP, etc. Despite its usefulness, constructing UCE in the standard model is challenging. The only known positive result is given by Brzuska and Mittelbach [BM14], who construct UCE with strongly computationally unpredictable one-query source assuming indistinguishability...

A recent line of research has introduced a systematic approach to explore the complexity of explicit construction problems through the use of meta problems, namely, the range avoidance problem (abbrev. $\textsf{Avoid}$) and the remote point problem (abbrev. $\textsf{RPP}$). The upper and lower bounds for these meta problems provide a unified perspective on the complexity of specific explicit construction problems that were previously studied independently. An interesting question largely...

In recent years, quantum computers and Shor’s quantum algorithm have been able to effectively solve NP (Non-deterministic Polynomial-time) problems such as prime factorization and discrete logarithm problems, posing a threat to current mainstream asymmetric cryptography, including RSA and Elliptic Curve Cryptography (ECC). As a result, the National Institute of Standards and Technology (NIST) in the United States call for Post-Quantum Cryptography (PQC) methods that include lattice-based...

DCT is a beyond-birthday-bound~(BBB) deterministic authenticated encryption~(DAE) mode proposed by Forler et al. in ACISP 2016, ensuring integrity by redundancy. The instantiation of DCT employs the BRW polynomial, which is more efficient than the usual polynomial in GCM by reducing half of the multiplication operations. However, we show that DCT suffers from a small stretch problem similar to GCM. When the stretch length $\tau$ is small, choosing a special $m$-block message, we can reduce...

We introduce a new cryptographic primitive, called Completely Anonymous Signed Encryption (CASE). CASE is a public-key authenticated encryption primitive, that offers anonymity for senders as well as receivers. A "case-packet" should appear, without a (decryption) key for opening it, to be a blackbox that reveals no information at all about its contents. To decase a case-packet fully - so that the message is retrieved and authenticated - a verifcation key is also required. Defining security...

We propose a new framework to homomorphically evaluate Boolean functions using the Torus Fully Homomorphic Encryption (TFHE) scheme. Compared to previous approaches focusing on Boolean gates, our technique can evaluate more complex Boolean functions with several inputs using a single bootstrapping. This allows us to greatly reduce the number of bootstrapping operations necessary to evaluate a Boolean circuit compared to previous works, thus achieving significant improvements in terms of...

In this work, we construct the first digital signature (SIG) and public-key encryption (PKE) schemes with almost tight multi-user security under adaptive corruptions based on the learning-with-errors (LWE) assumption in the standard model. Our PKE scheme achieves almost tight IND-CCA security and our SIG scheme achieves almost tight strong EUF-CMA security, both in the multi-user setting with adaptive corruptions. The security loss is quadratic in the security parameter, and independent of...

In oblivious finite automata evaluation, one party holds a private automaton, and the other party holds a private string of characters. The objective is to let the parties know whether the string is accepted by the automaton or not, while keeping their inputs secret. The applications include DNA searching, pattern matching, and more. Most of the previous works are based on asymmetric cryptographic primitives, such as homomorphic encryption and oblivious transfer. These primitives are...

Efficiently and securely removing encrypted redundant data with cross-user in the cloud is challenging. Convergent Encryption (CE) is difficult to resist dictionary attacks for its deterministic tag. Server-aided mechanism is against such attacks while it may exist collusion. Focus on multimedia data, this paper proposes an efficient and secure fuzzy deduplication system without any additional servers. We also propose a notion of preverification of label consistency to compensate for the...

At Asiacrypt 2021, Baksi et al. introduced DEFAULT, the first block cipher designed to resist differential fault attacks (DFA) at the algorithm level, boasting of a 64-bit DFA security. The cipher initially employed a straightforward key schedule, where a single key was XORed in all rounds, and the key schedule was updated by incorporating round-independent keys in a rotating fashion. However, during Eurocrypt 2022, Nageler et al. presented a DFA attack that exposed vulnerabilities in the...

Witness encryption is a generalization of public-key encryption where the public key can be any NP statement x and the associated decryption key is any witness w for x. While early constructions of witness encryption relied on multilinear maps and indistinguishability obfuscation (iO), recent works have provided direct constructions of witness encryption that are more efficient than iO (and also seem unlikely to yield iO). Motivated by this progress, we revisit the possibility of using...

A Key Derivation Function (KDF) generates a uniform and highly random key-stream from weakly random key material. KDFs are broadly used in various security protocols such as digital signatures and key exchange protocols. HKDF, the most deployed KDF in practice, is based on the extract-then-expand paradigm. It is presently used, among others, in the Signal Protocol for end-to-end encrypted messaging. HKDF is a generic KDF for general input sources and thus is not optimized for...

Gadget decomposition is widely used in lattice based cryptography, especially homomorphic encryption (HE) to keep the noise growth slow. If it is randomized following a subgaussian distribution, it is called subgaussian (gadget) decomposition which guarantees that we can bound the noise contained in ciphertexts by its variance. This gives tighter and cleaner noise bound in average case, instead of the use of its norm. Even though there are few attempts to build efficient such algorithms,...

Garbled circuits are a fundamental cryptographic primitive that allows two or more parties to securely evaluate an arbitrary Boolean circuit without revealing any information beyond the output using a constant number of communication rounds. Garbled circuits have been introduced by Yao (FOCS’86) and generalized to the multi-party setting by Beaver, Micali and Rogaway (STOC’90). Since then, several works have improved their efficiency by providing different garbling schemes and several...

In 2002, Barak and Goldreich introduced the notion of a universal argument and constructed an interactive universal argument for non-deterministic computations based on polynomially hard collision-resistant hash functions. Since then, and especially in recent years, there have been tremendous developments in the construction of non-interactive succinct arguments for deterministic computations under standard hardness assumptions. However, the constructed succinct arguments can be proven...

We show how to obfuscate pseudo-deterministic quantum circuits in the classical oracle model, assuming the quantum hardness of learning with errors. Given the classical description of a quantum circuit $Q$, our obfuscator outputs a quantum state $\ket{\widetilde{Q}}$ that can be used to evaluate $Q$ repeatedly on arbitrary inputs. Instantiating the classical oracle using any candidate post-quantum indistinguishability obfuscator gives us the first candidate construction of...

Dynamic Symmetric Searchable Encryption (SSE) enables a user to outsource the storage of an encrypted database to an untrusted server, while retaining the ability to privately search and update the outsourced database. The performance bottleneck of SSE schemes typically comes from their I/O efficiency. Over the last few years, a line of work has substantially improved that bottleneck. However, all existing I/O-efficient SSE schemes have a common limitation: they are not forward-secure. Since...

A hinting pseudorandom generator (PRG) is a potentially stronger variant of PRG with a ``deterministic'' form of circular security with respect to the seed of the PRG (Koppula and Waters, CRYPTO 2019). Hinting PRGs enable many cryptographic applications, most notably CCA-secure public-key encryption and trapdoor functions. In this paper, we study cryptographic primitives with the hinting property, yielding the following results: We present a novel and conceptually simpler approach for...

The One-Way to Hiding (O2H) Lemma is a central component of proofs of chosen-ciphertext attack (CCA) security of practical public-key encryption schemes using variants of the Fujisaki-Okamoto (FO) transform in the Quantum Random Oracle Model (QROM). Recently, Kuchta et al. (EUROCRYPT ’20) introduced a new QROM proof technique, called Measure-Rewind-Measure (MRM), giving an improved variant of the O2H lemma, with a new security reduction that does not suffer from a square-root advantage...

A (single server) private information retrieval (PIR) allows a client to read data from a public database held on a remote server, without revealing to the server which locations she is reading. In a doubly efficient PIR (DEPIR), the database is first preprocessed, but the server can subsequently answer any client's query in time that is sub-linear in the database size. Prior work gave a plausible candidate for a public-key variant of DEPIR, where a trusted party is needed to securely...

DME is a multivariate public key cryptosystem based on the composition of linear and exponential maps that allow the polynomials of the public key to be of a very high degree. A previous version of DME was presented to the NIST call (in the KEM category). The new version of DME adds one or two extra rounds of exponentials to the original two rounds. With this setting the composition gives a deterministic trapdoor one way permutation, which can be combined with an OAEP padding scheme for KEM...

Many modes of operations for block ciphers or tweakable block ciphers do not require invertibility from their underlying primitive. In this work, we study fixed-length Tweakable Pseudorandom Function (TPRF) with large domain extension, a novel primitive that can bring high security and significant performance optimizations in symmetric schemes, such as (authenticated) encryption. Our first contribution is to introduce a new design paradigm, derived from the Iterate-Fork-Iterate...

Many online applications, such as online file backup services, support the sharing of indexed data between a set of devices. These systems may offer client-side encryption of the data, so that the stored data is inaccessible to the online host. A potentially desirable goal in this setting would be to protect not just the contents of the backed-up files, but also their identifiers. However, as these identifiers are typically used for indexing, a deterministic consistent mapping across devices...

NJS is a cryptographic protection algorithm for relational databases with non-deterministic symmetric encryption, making it possible to search data with almost the same speed as a clear text search (depending on the parameterization). The algorithm has the characteristic of performing a fast encryption on the data and a slightly slower decryption that is only performed on the client workstation. The entire process of searching, changing, adding and deleting data is performed on the server...

In this work, we present the first fault injection analysis of the Number Theoretic Transform (NTT). The NTT is an integral computation unit, widely used for polynomial multiplication in several structured lattice-based key encapsulation mechanisms (KEMs) and digital signature schemes. We identify a critical single fault vulnerability in the NTT, which severely reduces the entropy of its output. This in turn enables us to perform a wide-range of attacks applicable to lattice-based KEMs as...

We propose a new paradigm for justifying the security of random oracle-based protocols, which we call the Augmented Random Oracle Model (AROM). We show that the AROM captures a wide range of important random oracle impossibility results. Thus a proof in the AROM implies some resiliency to such impossibilities. We then consider three ROM transforms which are subject to impossibilities: Fiat-Shamir (FS), Fujisaki-Okamoto (FO), and Encrypt-with-Hash (EwH). We show in each case how to obtain...

In this paper we describe a symmetric key algorithm that offers an unprecedented grade of confidentiality. Based on the uniqueness of the modular multiplicative inverse of a positive integer a modulo n and on its computability in a polynomial time, this non-deterministic cipher can easily and quickly handle keys of millions or billions of bits that an attacker does not even know the length of. The algorithm’s primary key is the modulo, while the ciphertext is given by the concatenation of...

The pseudorandom sampling of constant weight words, as it is currently implemented in cryptographic schemes like BIKE or HQC, is prone to the leakage of information on the seed being used for the pseudorandom number generation. This creates a vulnerability when the semantic security conversion requires a deterministic re-encryption. This observation was first made in [HLS21] about HQC and a timing attack was presented to recover the secret key. As suggested in [HLS21] a similar attack...

Well before large-scale quantum computers will be available, traditional cryptosystems must be transitioned to post-quantum (PQ) secure schemes. The NIST PQC competition aims to standardize suitable cryptographic schemes. Candidates are evaluated not only on their formal security strengths, but are also judged based on the security with regard to resistance against side-channel attacks. Although round 3 candidates have already been intensively vetted with regard to such attacks, one...

Higher-order power residues have enabled the construction of numerous public-key encryption schemes, authentication schemes, and digital signatures. Their explicit characterization is however challenging; an algorithm of Caranay and Scheidler computes $p$-th power residue symbols, with $p \le 13$ an odd prime, provided that primary elements in the corresponding cyclotomic field can be efficiently found. In this paper, we describe a new, generic algorithm to compute primary elements in...

The study of secure multi-party computation (MPC) has thus far been limited to the following two settings: every party is fully classical, or every party has quantum capabilities. This paper studies a notion of MPC that allows some classical and some quantum parties to securely compute a quantum functionality over their joint private inputs. In particular, we construct (constant-round, composable) protocols for blind and verifiable classical delegation of quantum computation, and give...

Lossy trapdoor functions, introduced by Peikert and Waters (STOC '08), can be initialized in one of two indistinguishable modes: in injective mode, the function preserves all information about its input, and can be efficiently inverted given a trapdoor, while in lossy mode, the function loses some information about its input. Such functions have found countless applications in cryptography, and can be constructed from a variety of number-theoretic or algebraic ``Cryptomania'' assumptions. ...

The three body problem is the founding problem of deterministic chaos theory. In this article is proposed a new stream cipher algorithm based on a mathematical structure similar to that underlying the 3 body poblem. Is also proposed to use said structure for the design of new bloc ciphers and hash functions algorithms.

Rasta and Dasta are two fully homomorphic encryption friendly symmetric-key primitives proposed at CRYPTO 2018 and ToSC 2020, respectively. We point out that the designers of Rasta and Dasta neglected an important property of the $\chi$ operation. Combined with the special structure of Rasta and Dasta, this property directly leads to significantly improved algebraic cryptanalysis. Especially, it enables us to theoretically break 2 out of 3 instances of full Agrasta, which is the aggressive...

Several recent proposals of efficient public-key encryption are based on variants of the polynomial learning with errors problem ($\mathsf{PLWE}^f$) in which the underlying polynomial ring $\mathbb{Z}_q[x]/f$ \ is replaced with the (related) modular integer ring $\mathbb{Z}_{f(q)}$; the corresponding problem is known as Integer Polynomial Learning with Errors ($\mathsf{I-PLWE}^f$). Cryptosystems based on $\mathsf{I-PLWE}^f$ and its variants can exploit optimised big-integer arithmetic to...

This research revisits the fundamental problem of processing privacy-preserving Boolean queries over outsourced databases on untrusted public clouds. Many current Searchable Encryption (SE) schemes try to seek an appropriate trade-off between security and efficiency, yet most of them suffer from an unacceptable query leakage due to their conjunctive/disjunctive terms that are processed individually. We show, however, this trade-off still can be deeply optimized for more security. We consider...

Cryptographic tools like proof systems, multi-party computation, and fully homomorphic encryption are usually applied to computations expressed as systems of arithmetic constraints. In practice, this means that these applications rely on compilers from high-level programming languages (like C) to such constraints. This compilation task is challenging, but not entirely new: the software verification community has a rich literature on compiling programs to logical constraints (like SAT or...

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...

We consider the problem of verifiable and private delegation of computation [Gennaro et al. CRYPTO'10] in which a client stores private data on an untrusted server and asks the server to compute functions over this data. In this scenario we aim to achieve three main properties: the server should not learn information on inputs and outputs of the computation (privacy), the server cannot return wrong results without being caught (integrity), and the client can verify the correctness of the...

This paper gives the first definitions and constructions for incremental pseudo-random functions (IPRFs). The syntax is nonce based. (Algorithms are deterministic but may take as input a non-repeating quantity called a nonce.) The design approach is modular. First, given a scheme secure only in the single-document setting (there is just one document on which incremental updates are being performed) we show how to generically build a scheme that is secure in the more realistic multi-document...

Boneh et al. proposed the cryptographic primitive public key encryption with keyword search (PEKS) to search on encrypted data without exposing the privacy of the keyword. Most standard PEKS schemes are vulnerable to inside keyword guessing attacks (KGA), i.e., a malicious server may generate a ciphertext by its own and then to guess the keyword of the trapdoor by testing. Huang et al. solved this problem by proposing the public-key authenticated encryption with keyword search (PAEKS)...

Public key encryption with keyword search (PEKS) is first introduced by Boneh et al. enabling a cloud server to search on encrypted data without leaking any information of the keyword. In almost all PEKS schemes, the privacy of trapdoor is vulnerable to inside keyword guessing attacks (KGA), i.e., the server can generate the ciphertext by its own and then run the test algorithm to guess the keyword contained in the trapdoor. To sole this problem, Huang et al. proposed the public-key...

Randomness is typically thought to be essential for zero knowledge protocols. Following this intuition, Goldreich and Oren (Journal of Cryptology 94) proved that auxiliary-input zero knowledge cannot be achieved with a deterministic prover. On the other hand, positive results are only known in the honest-verifier setting, or when the prover is given at least a restricted source of entropy. We prove that removing (or just ...

Privacy protection and scalability are significant issues with blockchain. We propose an anonymous probabilistic payment under the general functionality for solving them. We consider the situation that several payers pay several payees through a tumbler. We have mediated the tumbler of the payment channel hub between payers and payees. Unlinkability means that the link, which payer pays which payee via the tumbler, is broken. A cryptographic puzzle plays a role in controlling the...

As both notions employ the same key-evolution paradigm, Bellare \emph{et al.} (CANS 2017) study combining forward security with leakage resilience. The idea is for forward security to serve as a hedge in case at some point the full key gets exposed from the leakage. In particular, Bellare \emph{et al.} combine forward security with \emph{continual} leakage resilience, dubbed FS+CL. Our first result improves on Bellare \emph{et al.}'s FS+CL secure PKE scheme by building one from any...

We present a new general framework for constructing compact and adaptively secure attribute-based encryption (ABE) schemes from $k$-Lin in asymmetric bilinear pairing groups. Previously, the only construction [Kowalczyk and Wee, Eurocrypt '19] that simultaneously achieves compactness and adaptive security from static assumptions supports policies represented by Boolean formulae. Our framework enables supporting more expressive policies represented by arithmetic branching programs. Our...

Classically, selective-opening attack (SOA) has been studied for randomized primitives, like randomized encryption schemes and commitments. The study of SOA for deterministic primitives, which presents some unique challenges, was initiated by Bellare et al. (PKC 2015), who showed negative results. Subsequently, Hoang et al. (ASIACRYPT 2016) showed positive results in the non-programmable random oracle model. Here we show the first positive results for SOA security of deterministic...

We introduce the notion of Witness Maps as a cryptographic notion of a proof system. A Unique Witness Map (UWM) deterministically maps all witnesses for an $\mathbf{NP}$ statement to a single representative witness, resulting in a computationally sound, deterministic-prover, non-interactive witness independent proof system. A relaxation of UWM, called Compact Witness Map (CWM), maps all the witnesses to a small number of witnesses, resulting in a ``lossy'' deterministic-prover,...

We present Daence, a deterministic authenticated cipher based on a pseudorandom function family and a universal hash family, similar to SIV. We recommend instances with Salsa20 or ChaCha, and Poly1305, for high performance, high security, and easy deployment.

Distributed computational networks allow for effective hardware encryption systems and the rise of Quantum level encryption as well for Qubit based processing. Part of the reason distributed architecture can lead to Qubit level encryption is similar mechanisms applied to cryptographic hashing. In the work presented in this paper, we will look at the decentralized-internet SDK and protocol, grid computing architecture, and mathematical approaches to parallel Qubit-based processing. The...

Authenticated encryption schemes are usually expected to offer confidentiality and authenticity. In case of release of unverified plaintext (RUP), an adversary gets separated access to the decryption and verification functionality, and has more power in breaking the scheme. Andreeva et al. (ASIACRYPT 2014) formalized RUP security using plaintext awareness, informally meaning that the decryption functionality gives no extra power in breaking confidentiality, and INT-RUP security, covering...

Data, an important asset in digital economy, has fueled the emergence of a new data trading market. Big data market can efficiently promote data trading and further increases the utility of data. However, to realize effective data trading, several challenges needs to be resolved. First, it needs to resolve disputes over data availability in the data trad- ing. Second, atomic exchange and payment fairness between the seller and the buyer are hard to guarantee. Third, data trading platform is...

Trapdoor functions (TDFs) are one of the fundamental building blocks in cryptography. Studying the underlying assumptions and the efficiency of the resulting instantiations is therefore of both theoretical and practical interest. In this work we improve the input-to-image rate of TDFs based on the Diffie-Hellman problem. Specically, we present: \begin{enumerate} \item A rate-1 TDF from the computational Diffie-Hellman (CDH) assumption, improving the result of Garg, Gay, and Hajiabadi...

Memory fault attacks, inducing errors in computations, have been an ever-evolving threat to cryptographic schemes since their discovery for cryptography by Boneh et al. (Eurocrypt 1997). Initially requiring physical tampering with hardware, the software-based rowhammer attack put forward by Kim et al. (ISCA 2014) enabled fault attacks also through malicious software running on the same host machine. This led to concerning novel attack vectors, for example on deterministic signature schemes,...

We give a method to transform any indistinguishability obfuscator that suffers from correctness errors into an indistinguishability obfuscator that is $\textit{perfectly}$ correct, assuming hardness of Learning With Errors (LWE). The transformation requires sub-exponential hardness of the obfuscator and of LWE. Our technique also applies to eliminating correctness errors in general-purpose functional encryption schemes, but here it is sufficient to rely on the polynomial hardness of the...

We bypass impossibility results for the deterministic encryption of public-key-dependent messages, showing that, in this setting, the classical Encrypt-with-Hash scheme provides message-recovery security, across a broad range of message distributions. The proof relies on a new variant of the forking lemma in which the random oracle is reprogrammed on just a single fork point rather than on all points past the fork.

At CRYPTO 2017, Rosca et al. introduce a new variant of the Learning With Errors (LWE) problem, called the Middle-Product LWE (MP-LWE). The hardness of this new assumption is based on the hardness of the Polynomial LWE (P-LWE) problem parameterized by a set of polynomials, making it more secure against the possible weakness of a single defining polynomial. As a cryptographic application, they also provide an encryption scheme based on the MP-LWE problem. In this paper, we propose a...

Waters [Crypto, 2012] provided the first attribute based encryption scheme ABE for Deterministic Finite Automata (DFA) from a parametrized or ``q-type'' assumption over bilinear maps. Obtaining a construction from static assumptions has been elusive, despite much progress in the area of ABE. In this work, we construct the first attribute based encryption scheme for DFA from static assumptions on pairings, namely, the DLIN assumption. Our scheme supports unbounded length inputs, unbounded...

We present the first attribute-based encryption (ABE) scheme for deterministic finite automaton (DFA) based on static assumptions in bilinear groups; this resolves an open problem posed by Waters (CRYPTO 2012). Our main construction achieves selective security against unbounded collusions under the standard $k$-linear assumption in prime-order bilinear groups, whereas previous constructions all rely on $q$-type assumptions.

Constructing Attribute Based Encryption (ABE) [SW05] for uniform models of computation from standard assumptions, is an important problem, about which very little is known. The only known ABE schemes in this setting that i) avoid reliance on multilinear maps or indistinguishability obfuscation, ii) support unbounded length inputs and iii) permit unbounded key requests to the adversary in the security game, are by Waters from Crypto, 2012 [Wat12] and its variants. Waters provided the first...

[Modified slightly because MathJax doesn't render $U^{notbot}$ correctly] We revisit the construction of IND-CCA secure key encapsulation mechanisms (KEM) from public-key encryption schemes (PKE). We give new, tighter security reductions for several constructions. Our main result is a tight reduction for the security of the $U^{notbot}$-transform of Hofheinz, Hövelmanns, and Kiltz (TCC'17) which turns OW-CPA secure deterministic PKEs into IND-CCA secure KEMs. This result is enabled by a new...

Being the most widely used and comprehensive standard for hardware security modules, cryptographic tokens and smart cards, PKCS#11 has been the subject of academic study for years. PKCS#11 provides a key store that is separate from the application, so that, ideally, an application never sees a key in the clear. Again and again, researchers have pointed out the need for an import/export mechanism that ensures the integrity of the permissions associated to a key. With version 2.40, for the...

The combination of universal hashing and encryption is a fundamental paradigm for the construction of symmetric-key MACs, dating back to the seminal works by Wegman and Carter, Shoup, and Bernstein. While fully sufficient for many practical applications, the Wegman-Carter construction, however, is well-known to break if nonces are ever repeated, and provides only birthday-bound security if instantiated with a permutation. Those limitations inspired the community to several recent proposals...

Encrypted computing is an emerging field in which inputs, outputs and intermediates are maintained in encrypted form in a processor, conferring security on user data against the operator and operating system as adversaries, which run unencrypted in the same machine. Systems that pass encrypted addresses to memory without decryption close a major attack vector and allow off-the-shelf memory to be used. But that makes memory unreliable from the program's perspective, as the many different...

Concrete security proofs give upper bounds on the attacker's advantage as a function of its time/query complexity. Cryptanalysis suggests however that other resource limitations - most notably, the attacker's memory - could make the achievable advantage smaller, and thus these proven bounds too pessimistic. Yet, handling memory limitations has eluded existing security proofs. This paper initiates the study of time-memory trade-offs for basic symmetric cryptography. We show that schemes like...

We present several transformations that combine a set of attribute-based encryption (ABE) schemes for simpler predicates into a new ABE scheme for more expressive composed predicates. Previous proposals for predicate compositions of this kind, the most recent one being that of Ambrona et.al. at Crypto'17, can be considered static (or partially dynamic), meaning that the policy (or its structure) that specifies a composition must be fixed at the setup. Contrastingly, our transformations are...

We construct deterministic public key encryption secure for any constant number of arbitrarily correlated computationally unpredictable messages. Prior works required either random oracles or non-standard knowledge assumptions. In contrast, our constructions are based on the exponential hardness of DDH, which is plausible in elliptic curve groups. Our central tool is a new trapdoored extremely lossy function, which modifies extremely lossy functions by adding a trapdoor.

Algebraic structure lies at the heart of much of Cryptomania as we know it. An interesting question is the following: instead of building (Cryptomania) primitives from concrete assumptions, can we build them from simple Minicrypt primitives endowed with additional algebraic structure? In this work, we affirmatively answer this question by adding algebraic structure to the following Minicrypt primitives: • One-Way Function (OWF) • Weak Unpredictable Function (wUF) • Weak Pseudorandom...

There only exists one deterministic identity-based encryption (DIBE) scheme which is adaptively secure in the auxiliary-input setting, under the learning with errors (LWE) assumption. However, the master public key consists of $\mathcal{O}(\lambda)$ basic matrices. In this paper, we consider to construct adaptively secure DIBE schemes with more compact public parameters from the LWE problem. On the one hand, we gave a generic DIBE construction from lattice-based programmable hash functions...

We develop techniques for constructing trapdoor functions (TDFs) with short image size and advanced security properties. Our approach builds on the recent framework of Garg and Hajiabadi [CRYPTO 2018]. As applications of our techniques, we obtain -- The first construction of deterministic-encryption schemes for block-source inputs (both for the CPA and CCA cases) based on the Computational Diffie-Hellman (CDH) assumption. Moreover, by applying our efficiency-enhancing techniques, we obtain...

This paper studies indistinguishability against quantum chosen-ciphertext attacks (IND-qCCA security) of key-encapsulation mechanisms (KEMs) in quantum random oracle model (QROM). We show that the SXY conversion proposed by Saito, Yamakawa, and Xagawa (EUROCRYPT 2018) and the HU conversion proposed by Jiang, Zhang, and Ma (PKC 2019) turn a weakly-secure deterministic public-key encryption scheme into an IND-qCCA-secure KEM scheme in the QROM. The proofs are very similar to those for the...

SUM-ECBC (Yasuda, CT-RSA 2010) is the first beyond birthday bound (BBB) secure block cipher based deterministic MAC. After this work, some more BBB secure deterministic MACs have been proposed, namely PMAC_Plus (Yasuda, CRYPTO 2011), 3kf9 (Zhang et al., ASIACRYPT 2012) and LightMAC_Plus (Naito, ASIACRYPT 2017). In this paper, we have abstracted out the inherent design principle of all these BBB secure MACs and present a generic design paradigm to construct a BBB secure pseudo random...

In this paper, we give a no-signaling linear probabilistically checkable proof (PCP) system for polynomial-time deterministic computation, i.e., a PCP system for P such that (1) the honest PCP oracle is a linear function and (2) the soundness holds against any (computational) no-signaling cheating prover, who is allowed to answer each query according to a distribution that depends on the entire query set in a certain way. To the best of our knowledge, our construction is the first PCP system...

This paper highlights a particular construction of a correct KEM without failures and without ciphertext expansion from any correct deterministic PKE, and presents a simple tight proof of ROM IND-CCA2 security for the KEM assuming merely OW-CPA security for the PKE. Compared to previous proofs, this proof is simpler, and is also factored into smaller pieces that can be audited independently. In particular, this paper introduces the notion of ``IND-Hash'' security and shows that this allows a...

Abstract. This work describes a fast fully homomorphic encryption scheme over the torus (TFHE), that revisits, generalizes and improves the fully homomorphic encryption (FHE) based on GSW and its ring variants. The simplest FHE schemes consist in bootstrapped binary gates. In this gate bootstrapping mode, we show that the scheme FHEW of [29] can be expressed only in terms of external product between a GSW and a LWE ciphertext. As a consequence of this result and of other optimizations, we...

Nowadays it is well known that randomness may fail due to bugs or deliberate randomness subversion. As a result, the security of traditional public-key encryption (PKE) cannot be guaranteed any more. Currently there are mainly three approaches dealing with the problem of randomness failures: deterministic PKE, hedged PKE, and nonce-based PKE. However, these three approaches only apply to different application scenarios respectively. Since the situations in practice are dynamic and very...

Statistical analysis of ciphertexts has been recently used to carry out devastating inference attacks on deterministic encryption (Naveed, Kamara, and Wright, CCS 2015), order-preserving/revealing encryption (Grubbs et al., S&P 2017), and searchable encryption (Pouliot and Wright, CCS 2016). At the heart of these inference attacks is classical frequency analysis. In this paper, we propose and evaluate another classical technique, homophonic encoding, as a means to combat these attacks. We...

In order to be useful in the real world, efficient cryptographic constructions often reveal, or ``leak,'' more information about their plaintext than one might desire. Up until now, the approach for addressing leakage when proposing a new cryptographic construction has focused entirely on qualifying exactly what information is leaked. Unfortunately there has been no way to predict what the real-world impact of that leakage will be. In this paper, we argue in favor of an analytical...

Key-encapsulation mechanisms secure against chosen ciphertext attacks (IND-CCA-secure KEMs) in the quantum random oracle model have been proposed by Boneh, Dagdelen, Fischlin, Lehmann, Schafner, and Zhandry (CRYPTO 2012), Targhi and Unruh (TCC 2016-B), and Hofheinz, Hövelmanns, and Kiltz (TCC 2017). However, all are non-tight and, in particular, security levels of the schemes obtained by these constructions are less than half of original security levels of their building blocks. In this...

We consider Symmetric Searchable Encryption with Sharing and Unsharing (SSEwSU), a notion that models Symmetric Searchable Encryption (SSE) in a multi-user setting in which documents can be dynamically shared and unshared among users. Previous works on SSE involving multiple users have assumed that all users have access to the same set of documents and/or their security models assume that all users in the system are trusted. As in SSE, every construction of a SSEwSU will be a trade-off...

Austrin, Chung, Mahmoody, Pass and Seth (Crypto'14) studied the notion of bitwise $p$-tampering attacks over randomized algorithms in which an efficient `virus' gets to control each bit of the randomness with independent probability $p$ in an online way. The work of Austrin et al. showed how to break certain `privacy primitives' (e.g., encryption, commitments, etc.) through bitwise $p$-tampering, by giving a bitwise $p$-tampering biasing attack for increasing the average $E[f(U_n)]$ of...

This paper contributes to understanding the interplay of security notions for PKE, KEMs, and DEMs, in settings with multiple users, challenges, and instances. We start analytically by first studying (a) the tightness aspects of the standard hybrid KEM+DEM encryption paradigm, (b) the inherent weak security properties of all deterministic DEMs due to generic key-collision attacks in the multi-instance setting, and (c) the negative effect of deterministic DEMs on the security of hybrid...

Write-Only Oblivious RAM (WoORAM) protocols provide privacy by encrypting the contents of data and also hiding the pattern of write operations over that data. WoORAMs provide better privacy than plain encryption and better performance than more general ORAM schemes (which hide both writing and reading access patterns), and the write-oblivious setting has been applied to important applications of cloud storage synchronization and encrypted hidden volumes. In this paper, we introduce an...

We propose a new mode of operation called ZMAC allowing to construct a (stateless and deterministic) message authentication code (MAC) from a tweakable block cipher (TBC). When using a TBC with $n$-bit blocks and $t$-bit tweaks, our construction provides security (as a variable-input-length PRF) beyond the birthday bound with respect to the block-length $n$ and allows to process $n+t$ bits of inputs per TBC call. In comparison, previous TBC-based modes such as PMAC1, the TBC-based...

Hedged PKE schemes are designed to provide useful security when the per-message randomness fails to be uniform, say, due to faulty implementations or adversarial actions. A simple and elegant theoretical approach to building such schemes works like this: Synthesize fresh random bits by hashing all of the encryption inputs, and use the resulting hash output as randomness for an underlying PKE scheme. The idea actually goes back to the Fujisaki-Okamoto transform for turning CPA-secure...

We describe a new reconciliation method for Ring-LWE that has a significantly smaller failure rate than previous proposals while reducing ciphertext size and the amount of randomness required. It is based on a simple, deterministic variant of Peikert's reconciliation that works with our new ``safe bits'' selection and constant-time error correction techniques. The new method does not need randomized smoothing to achieve non-biased secrets. When used with the very efficient ``New Hope''...

At CT-RSA 2017, List and Nandi proposed two variable input length pseudorandom functions (VI-PRFs) called PMACx and PMAC2x, and a deterministic authenticated encryption scheme called SIVx. These schemes use a tweakable block cipher (TBC) as the underlying primitive, and are provably secure up to the query complexity of $2^n$, where $n$ denotes the block length of the TBC. In this paper, we falsify the provable security claims by presenting concrete attacks. We show that with the query...

We propose a Somewhat Homomorphic Encryption (SHE) scheme based on the Learning With Rounding (LWR) problem. The LWR problem is somewhat similar to the more classical Learning With Errors (LWE) and was proposed as a deterministic variant of it and setting up an LWR instance does not require the generation of gaussian noise. Thus our SHE scheme can be instantiated without the need for expensive Gaussian noise sampling. Our initial scheme provides lower ciphertext sizes for small plaintext...

Assume that a symmetric encryption scheme has been deployed and used with a secret key. We later must change the encryption scheme in a way that preserves the ability to decrypt (a subset of) previously encrypted plaintexts. Frequent real-world examples are migrating from a token-based encryption system for credit-card numbers to a format-preserving encryption (FPE) scheme, or extending the message space of an already deployed FPE. The ciphertexts may be stored in systems for which it is not...

We study the security of authenticated encryption based on a stream cipher and a universal hash function. We consider ChaCha20-Poly1305 and generic constructions proposed by Sarkar, where the generic constructions include 14 AEAD (authenticated encryption with associated data) schemes and 3 DAEAD (deterministic AEAD) schemes. In this paper, we analyze the integrity of these schemes both in the standard INT-CTXT notion and in the RUP (releasing unverified plaintext) setting called INT-RUP...