Registered attribute-based encryption (ABE) is a generalization of public-key encryption that enables fine-grained access control to encrypted data (like standard ABE), but without needing a central trusted authority. In a key-policy registered ABE scheme, users choose their own public and private keys and then register their public keys together with a decryption policy with an (untrusted) key curator. The key curator aggregates all of the individual public keys into a short master public...

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). ...

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...

Cloud storage offers convenient data access and sharing, but security concerns remain. Existing secure cloud storage solutions often lack essential features like data integrity, multi-cloud support, user-friendly file sharing, and efficient search. This paper proposes a novel secure cloud storage system that addresses these limitations. Our system uses distributed storage and attribute-based encryption to enhance data availability, access control, and user experience. It also enables private...

Fully Homomorphic Encryption (FHE) is a powerful technology that allows a cloud server to perform computations directly on ciphertexts. To overcome the overhead of sending and storing large FHE ciphertexts, the concept of FHE transciphering was introduced, allowing symmetric key encrypted ciphertexts to be transformed into FHE ciphertexts by deploying symmetric key decryption homomorphically. However, existing FHE transciphering schemes remain unauthenticated and malleable, allowing...

End-to-end encrypted cloud storage offers a way for individuals and organisations to delegate their storage needs to a third-party, while keeping control of their data using cryptographic techniques. We conduct a cryptographic analysis of various products in the ecosystem, showing that many providers fail to provide an adequate level of security. In particular, we provide an in-depth analysis of five end-to-end encrypted cloud storage systems, namely Sync, pCloud, Icedrive, Seafile, and...

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...

Attribute-based encryption (ABE) is a powerful primitive that has found applications in important real-world settings requiring access control. Compared to traditional public-key encryption, ABE has established itself as a considerably more complex primitive that is additionally less efficient to implement. It is therefore paramount that the we can simplify the design of ABE schemes that are efficient, provide strong security guarantees, minimize the complexity in their descriptions and...

With the widespread development of cloud storage, searching over the encrypted data (without decryption) has become a crucial issue. Public key authenticated encryption with keyword search (PAEKS) retrieves encrypted data, and resists inside keyword guessing attacks (IKGAs). Most PAEKS schemes cannot support access control in multi-receiver models. To address this concern, attribute-based authenticated encryption with keyword search (ABAEKS) has been studied. However, the access privilege...

Privacy preserving systems often need to allow anonymity while requiring accountability. For anonymous clients, depending on application, this may mean banning/revoking their accounts, docking their reputation, or updating their state in some complex access control scheme. Frequently, these operations happen asynchronously when some violation, e.g., a forum post, is found well after the offending action occurred. Malicious clients, naturally, wish to evade this asynchronous negative...

Servan-Schreiber et al. (S&P 2023) presented a new notion called private access control lists (PACL) for function secret sharing (FSS), where the FSS evaluators can ensure that the FSS dealer is authorized to share the given function. Their construction relies on costly non-interactive secret-shared proofs and is not secure in post-quantum setting. We give a construction of PACL from publicly verifiable secret sharing (PVSS) under short integer solution (SIS). Our construction adapts the...

Privacy is a major concern in large-scale digital applications, such as cloud-computing, machine learning services, and access control. Users want to protect not only their plain data but also their associated attributes (e.g., age, location, etc). Functional encryption (FE) is a cryptographic tool that allows fine-grained access control over encrypted data. However, existing FE fall short as they are either inefficient and far from reality or they leak sensitive user-specific...

Attribute-Based Encryption (ABE) provides fine-grained access control to encrypted data and finds applications in various domains. The practicality of ABE schemes hinges on the balance between security and efficiency. The state-of-the-art adaptive secure ABE scheme, proven to be adaptively secure under standard assumptions (FAME, CCS'17), is less efficient compared to the fastest one (FABEO, CCS'22) which is only proven secure under the Generic Group Model (GGM). These traditional ABE...

Distributed Point Function (DPF) provides a way for a dealer to split a point function $f_{\alpha, \beta}$ into multiple succinctly described function-shares, where the function $f_{\alpha, \beta}$ for a special input $\alpha$, returns a special output value $\beta$, and returns a fixed value $0$ otherwise. As the security requirement, any strict subset of the function-shares reveals nothing about the function $f_{\alpha,\beta}$. However, each function-share can be individually evaluated on...

Attribute-based encryption (ABE) is a generalization of public-key encryption that enables fine-grained access control to encrypted data. In (ciphertext-policy) ABE, a central trusted authority issues decryption keys for attributes $x$ to users. In turn, ciphertexts are associated with a decryption policy $\mathcal{P}$. Decryption succeeds and recovers the encrypted message whenever $\mathcal{P}(x) = 1$. Recently, Hohenberger, Lu, Waters, and Wu (Eurocrypt 2023) introduced the notion of...

Recent years have witnessed a significant development for functional encryption (FE) in the multi-user setting, particularly with multi-client functional encryption (MCFE). The challenge becomes more important when combined with access control, such as attribute-based encryption (ABE), which was actually not covered syntactically by the public-key FE nor semantically by the secret-key MCFE frameworks. On the other hand, as for complex primitives, many works have studied the admissibility of...

With the rapidly evolving landscape of cryptography, blockchain technology has advanced to cater to diverse user requirements, leading to the emergence of a multi-chain ecosystem featuring various use cases characterized by distinct transaction speed and decentralization trade-offs. At the heart of this evolution lies digital signature schemes, responsible for safeguarding blockchain-based assets such as ECDSA, Schnorr, and EdDSA, among others. However, a critical gap exists in the...

Attribute-based cryptography allows fine-grained control on the use of the private key. In particular, attribute-based signature (ABS) specifies the capabilities of the signer, which can only sign messages associated to a policy that is authorized by his set of attributes. Furthermore, we can expect signature to not leak any information about the identity of the signer. ABS is a useful tool for identity-preserving authentication process which requires granular access-control, and can...

Decentralized Storage Networks (DSNs) represent a paradigm shift in data storage methodology, distributing and housing data across multiple network nodes rather than relying on a centralized server or data center architecture. The fundamental objective of DSNs is to enhance security, reinforce reliability, and mitigate censorship risks by eliminating a single point of failure. Leveraging blockchain technology for functions such as access control, ownership validation, and transaction...

Kyber KEM, the NIST selected PQC standard for Public Key Encryption and Key Encapsulation Mechanisms (KEMs) has been subjected to a variety of side-channel attacks, through the course of the NIST PQC standardization process. However, all these attacks targeting the decapsulation procedure of Kyber KEM either require knowledge of the ciphertexts or require to control the value of ciphertexts for key recovery. However, there are no known attacks in a blind setting, where the attacker does not...

The issue of data and information security on the internet and social network has become more serious and pervasive in recent years. Cryptography is used to solve security problems. However, message encryption cannot merely meet the intended goals because access control over the encrypted messages is required in some applications. To achieve these requirements, attribute-based encryption (ABE) is used. This type of encryption provides both security and access structure for the network users...

In order to provide access control on encrypted data, Attribute-based encryption (ABE) defines each user using a set of attributes. Fuzzy identity-based encryption (FIBE) is a variant of ABE that allows for a threshold access structure for users. To address the potential threat posed by future quantum computers, this paper presents a post-quantum fuzzy IBE scheme based on lattices. However, current lattice-based ABE schemes face challenges related to computational complexity and the length...

Attribute-Based Encryption is widely recognized as a leap forward in the field of public key encryption. It allows to enforce an access control on encrypted data. Decryption time in ABE schemes can be long depending on the number of attributes and pairing operations. This drawback hinders their adoption on a broader scale. In this paper, we propose a non-monotone CP-ABE scheme that has no restrictions on the size of attribute sets and policies, allows fast decryption and is adaptively...

The need for energy optimizations in modern systems forces CPU vendors to provide Dynamic Voltage Frequency Scaling (DVFS) interfaces that allow software to control the voltage and frequency of CPU cores. In recent years, the accessibility of such DVFS interfaces to adversaries has amounted to a plethora of fault attack vectors. In response, the current countermeasures involve either restricting access to DVFS interfaces or including additional compiler-based checks that let the DVFS fault...

Recently, Servan-Schreiber et al. (S&P 2023) proposed a new notion called private access control lists (PACL) for function secret sharing (FSS), where the FSS evaluators can ensure that the FSS dealer is authorized to share the given function with privacy assurance. In particular, for the secret sharing of a point function $f_{\alpha, \beta}$, namely distributed point function (DPF), the authors showed how to efficiently restrict the choice of $\alpha$ via a specific PACL scheme from...

Attribute-based encryption (ABE) is a popular type of public-key encryption that enforces access control cryptographically, and has spurred the proposal of many use cases. To satisfy the requirements of the setting, tailor-made schemes are often introduced. However, designing secure schemes---as well as verifying that they are secure---is notoriously hard. Several of these schemes have turned out to be broken, making them dangerous to deploy in practice. To overcome these shortcomings,...

The accelerated advances in information communication technologies have made it possible for enterprises to deploy large scale applications in a multi-server architecture (also known as cloud computing environment). In this architecture, a mobile user can remotely obtain desired services over the Internet from multiple servers by initially executing a single registration on a trusted registration server (RS). Due to the hazardous nature of the Internet, to protect user privacy and online...

Recently, Abdalla, Gong and Wee (Crypto 2020) provided the first functional encryption scheme for attribute-weighted sums (AWS), where encryption takes as input $N$ (unbounded) attribute-value pairs $\{\vec{x}_i, \vec{z}_i\}_{I \in [N]}$ where $\vec{x}_i$ is public and $\vec{z}_i$ is private, the secret key is associated with an arithmetic branching programs $f$, and decryption returns the weighted sum ${\sum}_{{i \in [N]}} f(\vec{x}_i)^\top \vec{z}_i$, leaking no additional information...

An attribute-based credential system enables users to prove possession of a credential and statements over certified attributes to verifiers in zero-knowledge while maintaining anonymity and unlinkability. In a relational anonymous credential system, users can further prove their relationship to other entities in their social graph, such as position in an organizational hierarchy or friends-of-friends status in an online social network graph, while protecting their own privacy and that of...

Profiling side-channel analysis (SCA) is widely used to evaluate the security of cryptographic implementations under worst-case attack scenarios. This method assumes a strong adversary with a fully controlled device clone, known as a profiling device, with full access to the internal state of the target algorithm, including the mask shares. However, acquiring such a profiling device in the real world is challenging, as secure products enforce strong life cycle protection, particularly on...

Commodity encrypted storage platforms (e.g., IceDrive, pCloud) permit data store and sharing across multiple users while preserving data confidentiality. However, end-to-end encryption may not be sufficient since it only offers confidentiality when the data is at rest or in transit. Meanwhile, sensitive information can be leaked from metadata representing activities during data operations (e.g., query, processing). Recent encrypted search platforms such as DORY (OSDI’20) or DURASIFT...

Zero-knowledge proofs are widely used in real-world applications for authentication, access control, blockchains, and cryptocurren- cies, to name a few. A core element in zero-knowledge proof systems is the underlying hash function, which plays a vital role in the effi- ciency of the proof system. While the traditional hash functions, such as SHA3 or BLAKE3 are efficient on CPU architectures, they perform poorly within zero-knowledge proof systems. This is pri- marily due to the...

Modern system-on-chip (SoC) designs are becoming prone to numerous security threats due to their critical applications and ever-growing complexity and size. Therefore, the early stage of the design flow requires comprehensive security verification. The control flow of an SoC, generally implemented using finite state machines (FSMs), is not an exception to this requirement. Any deviations from the desired flow of FSMs can cause serious security issues. On the other hand, the control FSMs may...

Vehicular Social Networks (VSNs) rely on data shared by users to provide convenient services. Data is outsourced to the cloud server and the distributed roadside unit in VSNs. However, roadside unit has limited resources, so that data sharing process is inefficient and is vulnerable to security threats, such as illegal access, tampering attack and collusion attack. In this article, to overcome the shortcomings of security, we define a chain tolerance semi-trusted model to describe the...

In this paper, we present a novel method for timestamping and data notarisation on a distributed ledger. The problem with on-chain hashes is that a cryptographic hash is a deterministic function that it allows the blockchain be used as an oracle that confirms whether potentially leaked data is authentic (timestamped or notarised by the user). Instead, we suggest using on-chain Pedersen commitments and off-chain zero knowledge proofs (ZKP) for designated verifiers to prove the link between...

Society appears to be on the verge of recognizing the need for control over sensitive data in modern web applications. Recently, many systems claim to give control to individuals, promising the preeminent goal of data sovereignty. However, despite recent attention, research and industry efforts are fragmented and lack a holistic system overview. In this paper, we provide the first transecting systematization of data sovereignty by drawing from a dispersed body of knowledge. We clarify the...

Anonymous or attribute-based credential (ABC) systems are a versatile and important cryptographic tool to achieve strong access control guarantees while simultaneously respecting the privacy of individuals. A major problem in the practical adoption of ABCs is their transferability, i.e., such credentials can easily be duplicated, shared or lent. One way to counter this problem is to tie ABCs to biometric features of the credential holder and to require biometric verification on every use....

Attribute-based encryption (ABE) is an asymmetric encryption method that allows expressive access granting mechanisms, with high applicability in modern IT infrastructure, such as Cloud or IoT systems. (Ezhilarasi et al., 2021; Touati and Challal, 2016) One open problem regarding ABE is using Boolean circuits as access structures. While Boolean Formulae were supported since the first ABE scheme proposed, there is still no efficient construction that supports Boolean circuits. We propose a...

We show how to embed a covert key exchange sub protocol within a regular TLS 1.3 execution, generating a stealth key in addition to the regular session keys. The idea, which has appeared in the literature before, is to use the exchanged nonces to transport another key value. Our contribution is to give a rigorous model and analysis of the security of such embedded key exchanges, requiring that the stealth key remains secure even if the regular key is under adversarial control. Specifically...

This paper presents the first decentralized multi-authority attribute-based inner product functional encryption (MA-ABIPFE) schemes supporting vectors of a priori unbounded lengths. The notion of AB-IPFE, introduced by Abdalla et al. [ASIACRYPT 2020], combines the access control functionality of attribute-based encryption (ABE) with the possibility of evaluating linear functions on encrypted data. A decentralized MA-ABIPFE defined by Agrawal et al. [TCC 2021] essentially enhances the ABE...

This paper introduces the first registered functional encryption RFE scheme tailored for linear functions. Distinctly different from classical functional encryption (FE), RFE addresses the key-escrow issue and negates the master key exfiltration attack. Instead of relying on a centralized trusted authority, it introduces a “key curator” - a fully transparent entity that does not retain secrets. In an RFE framework, users independently generate secret keys and subsequently register their...

HID Global is a major vendor of physical access control systems. In 2012, it introduced Seos, its newest and most secure contactless RFID credential technology, successfully remediating known flaws in predecessors iCLASS and Prox. Seos has been widely deployed to secure sensitive assets and facilities. To date, no published research has demonstrated a security flaw in Seos. We present a relay attack developed with inexpensive COTS hardware, including the Proxmark 3 RDV4. Our attack is...

The Extended Access Control (EAC) protocol for authenticated key agreement is mainly used to secure connections between machine-readable travel documents (MRTDs) and inspection terminals, but it can also be adopted as a universal solution for attribute-based access control with smart cards. The security of EAC is currently based on the Diffie-Hellman problem, which may not be hard when considering quantum computers. In this work we present PQ-EAC, a quantum-resistant version of the EAC...

Electronic Medical Records (EMRs) have been utilized in plentiful medical institutions due to their superior convenience and low storage overhead. Nevertheless, it is difficult for medical departments with disparate management regulations to share EMRs through secure communication channels since sensitive EMRs are prone to be tampered with. Therefore, the EMRs should be encrypted before being outsourced to the network servers. Public key Encryption with Keyword Search (PEKS) has the ability...

TLS termination, which is essential to network and security infrastructure providers, is an extremely latency sensitive operation that benefits from access to sensitive key material close to the edge. However, increasing regulatory concerns prompt customers to demand sophisticated controls on where their keys may be accessed. While traditional access-control solutions rely on a highly available centralized process to enforce access, the round-trip latency and decreased fault tolerance make...

We consider multi-party information-theoretic private computation. Such computation inherently requires the use of local randomness by the parties, and the question of minimizing the total number of random bits used for given private computations has received considerable attention in the literature. In this work we are interested in another question: given a private computation, we ask how many of the players need to have access to a random source, and how many of them can be...

This study presents a proof-of-concept for a cognitive-based authentication system that uses an individual's writing style as a unique identifier to grant access to a system. A machine learning SVM model was trained on these features to distinguish between texts generated by each user. The stylometric feature vector was then used as an input to a key derivation function to generate a unique key for each user. The experiment results showed that the developed system achieved up to 87.42\%...

Function Secret Sharing (FSS; Eurocrypt 2015) allows a dealer to share a function f with two or more evaluators. Given secret shares of a function f, the evaluators can locally compute secret shares of f(x) on an input x, without learning information about f. In this paper, we initiate the study of access control for FSS. Given the shares of f, the evaluators can ensure that the dealer is authorized to share the provided function. For a function family F and an access control list defined...

The tech industry is currently making the transition from Web 2.0 to Web 3.0, and with this transition, authentication and authorization have been reimag- ined. Users can now sign in to websites with their unique public/private key pair rather than generating a username and password for every site. How- ever, many useful features, like role-based access control, dynamic resource owner privileges, and expiration tokens, currently don’t have efficient Web 3.0 solutions. Our solution aims...

Sharing a secret efficiently amongst a group of participants is not easy since there is always an adversary / eavesdropper trying to retrieve the secret. In secret sharing schemes, every participant is given a unique share. When the desired group of participants come together and provide their shares, the secret is obtained. For other combinations of shares, a garbage value is returned. A threshold secret sharing scheme was proposed by Shamir and Blakeley independently. In this (n,t)...

The recent advent of cloud computing and IoT has made it imperative to store huge amount of data in the cloud servers. Enormous amount of data is also stored in the servers of big organizations. In organizations, it is not desirable for every member to have equal privileges to access the stored data. Threshold secret sharing schemes are widely used for implementing such access control mechanisms. The access privileges of the members also vary from one data packet to another. While...

In a world where everyone uses anonymous credentials for all access control needs, it is impossible to trace wrongdoers, by design. This makes legitimate controls, such as tracing illicit trade and terror suspects, impossible to carry out. Here, we propose a privacy-preserving blueprint capability that allows an auditor to publish an encoding $pk_A$ of the function $f(x,\cdot)$ for a publicly known function $f$ and a secret input $x$. For example, $x$ may be a secret watchlist, and...

Confidential Computing is the protection of data in use from access or modification by any unauthorized agent, including privileged software. For example, in Intel SGX (Client and Scalable versions) and TDX, AMD SEV, Arm CCA, and IBM Ultravisor this protection is implemented via access control policies. Some of these architectures also include memory protection schemes relying on cryptography, to protect against physical attacks. We review and classify such schemes, from academia and...

Traditional finance quantifies risk by collecting and vetting reputation information for an individual, such as credit scores or payment history. While decentralized finance (DeFi) is an exceptionally well-suited application of permissionless blockchains, it is severely constrained in its ability to reconcile identities and quantify associated transaction risk directly on-chain. Opening the ecosystem to a broad range of use cases requires consistent pseudonymity and quantifiable reputation....

Attribute-based encryption (ABE) enables fine-grained access control on encrypted data and has a large number of practical applications. This paper presents FABEO: faster pairing-based ciphertext-policy and key-policy ABE schemes that support expressive policies and put no restriction on policy type or attributes, and the first to achieve optimal, adaptive security with multiple challenge ciphertexts. We implement our schemes and demonstrate that they perform better than the state-of-the-art...

Restricting access to certified users is not only desirable for many blockchain applications, it is also legally mandated for decentralized finance (DeFi) applications to counter malicious actors. Existing solutions, however, are either (i) non-private, i.e., they reveal the link between users and their wallets to the authority granting credentials, or (ii) they introduce additional trust assumptions by relying on a decentralized oracle to verify anonymous credentials (ACs). To remove...

We propose a novel variant of functional encryption which supports ciphertext updates, dubbed ciphertext-updatable functional encryption (CUFE). Such a feature further broadens the practical applicability of the functional-encryption paradigm and allows for fine-grained access control even after a ciphertext is generated. Updating ciphertexts is carried out via so-called update tokens which a dedicated party can use to convert ciphertexts. However, allowing update tokens requires some care...

A significant shortcoming of traditional access control mechanisms is their heavy reliance on reference monitors. Being single points of failure, monitors need to run in protected mode and have permanent online presence in order to handle all access requests. Cryptographic access control offers an alternative solution that provides better scalability and deployability. It relies on security guarantees of the underlying cryptographic primitives and the appropriate key distribution/management...

Databases often require the flexibility to control which entities can access specific database records. Such access control is absent in works that provide private access to databases, namely private information retrieval (PIR) systems. In this paper, we show how to address this shortcoming by introducing Pirmission, the first practical single-server PIR system that allows the enforcement of access control policies. Pirmission’s mechanism does not even reveal whether the client passed or...

The time sequence-based outsourcing makes new demands for related access control continue to grow increasingly in cloud computing. In this paper, we propose a practical password-based access control framework for such media cloudization relying on content control based on the time-sequence attribute, which is designed over prime-order groups. First, the scheme supports multi-keyword search simultaneously in any monotonic boolean formulas, and enables media owner to control content...

Cloud-aided Internet of Things (IoT) overcomes the resource-constrained nature of the traditional IoT and develops rapidly. In a cloud-aided IoT system, users can remotely control the IoT devices or send specific instructions to them. In this case, if the user identity is not verified, adversaries can send fake and malicious instructions to the IoT devices, thereby compromising the security of the entire system. Thus, an authentication mechanism is indispensable to ensure security. In a...

Access Control Encryption (ACE) allows to control information flow between parties by enforcing a policy that specifies which user can send messages to whom. The core of the scheme is a sanitizer, i.e., an entity that ''sanitizes'' all messages by essentially re-encrypting the ciphertexts under its key. In this work we investigate the natural question of whether it is still possible to achieve some meaningful security properties in scenarios when such a sanitization step is not...

Anonymous credentials systems (ACs) are a powerful cryptographic tool for privacy-preserving applications and provide strong user privacy guarantees for authentication and access control. ACs allow users to prove possession of attributes encoded in a credential without revealing any information beyond them. A delegatable AC (DAC) system is an enhanced AC system that allows the owners of credentials to delegate the obtained credential to other users. This allows to model hierarchies as...

Attribute-based proxy re-encryption (AB-PRE) is one of the essential variants for proxy re-encryption. It allows a proxy with a re-encryption key to transform a ciphertext associated with an access policy and decryptable by a delegator into another ciphertext associated with a new access policy, thereafter other delegatees can decrypt. However, with AB-PRE, the proxy is to switch the underlying policies of all ciphertexts indiscriminately. The delegator cannot decide which ciphertext would...

Functional Encryption (FE) allows users who hold a specific decryption key, to learn a specific function of encrypted data while the actual plaintexts remain private. While FE is still in its infancy, it is our strong belief that in the years to come, this remarkable cryptographic primitive will have matured to the degree that will make it an integral part of access control systems, especially cloud-based ones. To this end, we believe it is of great importance to provide not only theoretical...

Unlike conventional ABE systems, which support Boolean attributes (with only 2 states: "1" and "0", or "Present" and "Absent"), weighted Attribute-based encryption schemes also support numerical values attached to attributes, and each terminal node of the access structure contains a threshold for a minimum weight. We propose a weighted ABE system, with access policy of logarithmic expansion, by dividing each weighted attribute in sub-attributes. On top of that, we show that the decryption...

Ciphertext-policy attribute-based encryption (CP-ABE) has attracted much interest from the practical community to enforce access control in distributed settings such as the Internet of Things (IoT). In such settings, encryption devices are often constrained, having small memories and little computational power, and the associated networks are lossy. To optimize both the ciphertext sizes and the encryption speed is therefore paramount. In addition, the master public key needs to be small...

Attribute based encryption (ABE) is a cryptographic technique allowing fine-grained access control by enabling one-to-many encryption. Existing ABE constructions suffer from at least one of the following limitations. First, single point of failure on security meaning that, once an authority is compromised, an adversary can either easily break the confidentiality of the encrypted data or effortlessly prevent legitimate users from accessing data; second, the lack of user and/or attribute...

Multi-Client Functional Encryption ($\mathsf{MCFE}$) and Multi-Input Functional Encryption ($\mathsf{MIFE}$) are very interesting extensions of Functional Encryption for practical purpose. They allow to compute joint function over data from multiple parties. Both primitives are aimed at applications in multi-user settings where decryption can be correctly output for users with appropriate functional decryption keys only. While the definitions for a single user or multiple users were quite...

Recently, Ateniese et al. (CRYPTO 2019) proposed a new cryptographic primitive called matchmaking encryption (ME), which provides fine-grained access control over encrypted data by allowing both the sender and receiver to specify access control policies. The encrypted message can be decrypted correctly if and only if the attributes of the sender and receiver simultaneously meet each other's specified policies. In current ME, when users from different organizations need secret communication,...

Attribute based cryptography enhances the chances of secure communication on large scale. There are several features of attribute based encryption which have been proposed as different protocols. Most of these are suitable for access control in large systems like cloud services. Very few protocols focus on reducing the computational overhead for lower end devices like Internet of Things sensors and actuators. Hence, it is desirable to have a mix of features in protocols for IoT architecture....

Coconut [NDSS 2019] is an attribute-based credential scheme with threshold issuance. We analyze its security properties. To this end, we define an ideal functionality for attribute-based access control with threshold issuance. We describe a construction that realizes our functionality. Our construction follows Coconut with a few changes. In particular, it modifies the protocols for blind issuance of credentials and for credential show so that user privacy holds against computationally...

Attribute-Based Encryption (ABE) is a cryptographic primitive which supports fine-grained access control on encrypted data, making it an appealing building block for many applications. Multi-Authority Attribute-Based Encryption (MA-ABE) is a generalization of ABE where the central authority is distributed across several independent parties. We provide the first MA-ABE scheme from prime-order pairings where no trusted setup is needed and where the attribute universe of each authority is...

With the advent of the Internet of Things (IoT), e-health has become one of the main topics of research. Due to the sensitivity of patient information, patient privacy seems challenging. Nowadays, patient data is usually stored in the cloud in healthcare programs, making it difficult for users to have enough control over their data. The recent increment in announced cases of security and surveillance breaches compromising patients' privacy call into question the conventional model, in which...

Attribute-based encryption (ABE) cryptographically implements fine-grained access control on data. As such, data can be stored by an entity that is not necessarily trusted to enforce access control, or an entity that is not even trusted to have access to the plaintext data at all. Instead, access control can be externally enforced by a trusted entity. Additionally, some multi-authority variants of ABE---which do not have a central authority---can effectively and securely implement access...

Attribute-based encryption (ABE) schemes by lattices are likely to resist quantum attacks, and can be widely applied to many Internet of Thing or cloud scenarios. One of the most attractive feature for ABE is the ability of fine-grained access control which provides an effective way to ensure data security. In this work, we propose an efficient ciphertext policy attribute-based encryption scheme based on hardness assumption of LWE. Being different from other similar schemes, a user's secret...

We provide a new technique for secret sharing and reconstruction for Boolean circuits, applicable in ABE systems. We show that our construction holds for Key-policy ABE and can be adapted also to Ciphertext-policy ABE. This is the most efficient solution for Attribute Based Encryption for circuits access structures using bilinear maps. Our KP-ABE system has decryption key of linear size in the number of attributes, and public parameters linear in the circuit size (Two public values for...

In TCC 2013, Boyen suggested the first lattice based construction of attribute based encryption (ABE) for the circuit class $NC1$. Unfortunately, soon after, a flaw was found in the security proof of the scheme. However, it remained unclear whether the scheme is actually insecure, and if so, whether it can be repaired. Meanwhile, the construction has been heavily cited and continues to be extensively studied due to its technical novelty. In particular, this is the first lattice based ABE...

This paper proposes the first cache timing side-channel attack on one of Apple’s mobile devices. Utilizing a recent, permanent exploit named checkm8, we reverse-engineered Apple’s BootROM and created a powerful toolkit for running arbitrary hardware security experiments on Apple’s in-house designed ARM systems-on-a-chip (SoC). Using this toolkit, we then implement an access-driven cache timing attack (in the style of PRIME+PROBE) as a proof-of-concept illustrator. The advanced hardware...

We present Spectrum, a high-bandwidth, metadata-private file broadcasting system. In Spectrum, a small number of broadcasters share a file with many subscribers via two or more non-colluding broadcast servers. Subscribers generate cover traffic by sending dummy files, hiding which users are broadcasters and which users are only consumers. Spectrum optimizes for a setting with few broadcasters and many subscribers—as is common to many real-world applications—to drastically improve throughput...

The notion of functional encryption (FE) was proposed as a generalization of plain public-key encryption to enable a much more fine-grained handling of encrypted data, with advanced applications such as cloud computing, multi-party computations, obfuscating circuits or Turing machines. While FE for general circuits or Turing machines gives a natural instantiation of the many cryptographic primitives, existing FE schemes are based on indistinguishability obfuscation or multilinear maps which...

Attribute-based encryption (ABE) is a cryptographic primitive which supports fine-grained access control on encrypted data, making it an appealing building block for many applications. Pair encodings (Attrapadung, EUROCRYPT 2014) are simple primitives that can be used for constructing fully secure ABE schemes associated to a predicate relative to the encoding. We propose a generic transformation that takes any pair encoding scheme (PES) for a predicate $P$ and produces a PES for its negated...

Internet of Things (IoT) promises a strong connection between digital and physical environments. Nevertheless, such framework comes with huge security vulnerabilities, due to the heterogeneous nature of devices and of the diversity of their provenance. Furthermore, the resource constraints of weaker devices, such as sensors, require a lightweight design of security protocols. In 2018, Liu et al. presented a new system with access control key updates and direct user revocation, that are...

A major concern in training and releasing machine learning models is to what extent the model contains sensitive information that the data holders do not want to reveal. Property inference attacks consider an adversary who has access to the trained model and tries to extract some global statistics of the training data. In this work, we study property inference in scenarios where the adversary can maliciously control part of the training data (poisoning data) with the goal of increasing the...

Logic access control enforces who can read and write data; the enforcement is typically performed by a fully trusted entity. At TCC 2016, Damg\aa rd et al. proposed Access Control Encryption (ACE) schemes where a predicate function decides whether or not users can read (decrypt) and write (encrypt) data, while the message secrecy and the users' anonymity are preserved against malicious parties. Subsequently, several ACE constructions with an arbitrary identity-based access policy have been...

Relay attacks pose a serious security threat to wireless systems, such as, contactless payment systems, keyless entry systems, or smart access control systems. Distance bounding protocols, which allow an entity to not only authenticate another entity but also determine whether it is physically close by, effectively mitigate relay attacks. However, secure implementation of distance bounding protocols, especially of the time critical challenge-response phase, has been a challenging task. In...

The Google Titan Security Key is a FIDO U2F hardware device proposed by Google (available since July 2018) as a two-factor authentication token to sign in to applications (e.g. your Google account). We present here a side-channel attack that targets the Google Titan Security Key’s secure element (the NXP A700X chip) by the observation of its local electromagnetic radiations during ECDSA signatures (the core cryptographic operation of the FIDO U2F protocol). This work shows that an attacker...

Applying access structure to encrypted sensitive data is one of the challenges in communication networks and cloud computing. Various methods have been proposed to achieve this goal, one of the most interesting of which is Attribute-Based Encryption (ABE). In ABE schemes, the access structure, which is defined as a policy, can be applied to the key or ciphertext. Thus, if the policy is applied to the key, it is called the Key Policy Attribute-Based Encryption (KP-ABE), and on the other hand,...

Smart grid has improved the security, efficiency of the power system and balanced the supply and demand by intelligent management, which enhanced stability and reliability of power grid. The key point to achieve them is real-time data and consume data sharing by using fine-grained policies. But it will bring the leakage of the privacy of the users and losing of control over data for data owners. The reported solutions can not give the best trade-off among the privacy protection, control over...

Oblivious RAM enables oblivious access to memory in the single-client setting, which may not be the best fit in the network setting. Multi-client oblivious RAM (MCORAM) considers a collaborative but untrusted environment, where a database owner selectively grants read access and write access to different entries of a confidential database to multiple clients. Their access pattern must remain oblivious not only to the server but also to fellow clients. This upgrade rules out many techniques...

The celebrated work of Gorbunov, Vaikuntanathan and Wee provided the first key policy attribute based encryption scheme (ABE) for circuits from the Learning With Errors (LWE) assumption. However, the arguably more natural ciphertext policy variant has remained elusive, and is a central primitive not yet known from LWE. In this work, we construct the first symmetric key ciphertext policy attribute based encryption scheme (CP-ABE) for all polynomial sized circuits from the learning with...

Access Control or authorization is referred to as the confinement of specific actions of an entity to perform an action. Blockchain driven access control mechanisms have gained considerable attention since applications for blockchain were found beyond the premises of cryptocurrencies. However, there are no systematic efforts to analyze existing empirical evidence. To this end, we aim to synthesize literature to understand the state-of-the-art in blockchain driven access control mechanisms...

There are lots of applications of inner-product functional encryption (IPFE). In this paper, we consider two important extensions of it. One is to enhance IPFE with access control such that only users with a pre-defined identity are allowed to compute the inner product, referred as identity-based inner-product functional encryption (IBIPFE). We formalize the definition of IBIPFE, and propose the first adaptive-secure IBIPFE scheme from Decisional Bilinear Diffie-Hellman (DBDH) assumption. In...

We initiate the study of multi-party functional encryption (MPFE) which unifies and abstracts out various notions of functional encryption which support distributed ciphertexts or secret keys, such as multi-input FE, multi-client FE, decentralized multi-client FE, multi-authority FE, dynamic decentralized FE, adhoc multi-input FE and such others. Using our framework, we identify several gaps in the literature and provide some constructions to fill these: 1) Multi-Authority ABE with Inner...

A hierarchical key assignment scheme (HKAS) is a method to assign some private information and encryption keys to a set of classes in a partially ordered hierarchy, so that the private information of a higher class together with some public information can be used to derive the keys of all classes lower down in the hierarchy. Historically, HKAS have been introduced to enforce multi-level access control, where it can be safely assumed that the public information is made available in some...

Along with the rapid development of cloud computing technology, containerization technology has drawn much attention from both industry and academia. In this paper, we perform a comparative measurement analysis of Docker-sec, which is a Linux Security Module proposed in 2018, and a new AppArmor profile generator called Lic-Sec, which combines Docker-sec with a modified version of LiCShield, which is also a Linux Security Module proposed in 2015. Docker-sec and LiCShield can be used to...

The supersingular isogeny key encapsulation (SIKE) protocol, as one of the post-quantum protocol candidates, is widely regarded as the best alternative for curve-based cryptography. However, the long latency, caused by the serial large-degree isogeny computation which is dominated by modular multiplications, has made it less competitive than most popular post-quantum candidates. In this paper, we propose a high-speed and low-latency architecture for our recently presented optimized SIKE...

Attribute-based encryption (ABE) is a promising type of cryptosystem achieving fine-grained access control on encrypted data. Revocable attribute-based encryption (RABE) is an extension of ABE that provides revocation mechanisms when user's attributes change, key exposure, and so on. In this paper, we propose two directly revocable ciphertext-policy attribute-based encryption (DR-ABE) schemes from lattices, which support flexible threshold access policies on multi-valued attributes,...

E-cash and cryptocurrency schemes have been a focus of applied cryptography for a long time. However, we acknowledge the continuing need for a cryptographic protocol that provides global scale, decentralized, secure, and fair delivery of donations. Such a protocol would replace central trusted entities (e.g., charity organizations) and guarantee the privacy of the involved parties (i.e., donors and recipients of the donations). In this work, we target this online donation problem and...

Proxy re-encryption (PRE), formalized by Blaze et al. in 1998, allows a proxy entity to delegate the decryption right of a ciphertext from one party to another without obtaining the information of the plaintext. In recent years, many studies have explored how to construct PRE schemes that support fine-grained access control for complex application scenarios, such as identity-based PRE and attribute-based PRE. Besides, in order to achieve more flexible access control, the predicate proxy...