Federated learning (FL) serves as a distributed machine learning framework that addresses the challenges of data silos while preserving data privacy. Specifically, FL enables multiple participants to collaboratively train a global model by sharing local updates without exposing their raw local data. Although FL achieves physical data isolation through local update sharing mechanisms, it still faces emerging security threats. On the one hand, adversaries may reconstruct sensitive data features or infer client attributes by analyzing local updates. On the other hand, clients might upload malicious updates to disrupt global model aggregation, causing performance degradation. To solve these issues, we propose an anonymous and Byzantine-robust FL scheme with secure and efficient aggregation. First, we propose a single-masking protocol that not only preserves data privacy but also enhances aggregation efficiency. Second, we eliminate client message metadata, such as source IP addresses and timestamps, through secure shuffling, achieving client anonymity in conjunction with the single-masking protocol. Additionally, we implement a baffle mechanism to resist the impact of malicious updates on the global model, thereby ensuring Byzantine robustness. Security analysis demonstrates that our scheme simultaneously preserves data privacy and identity anonymity. Experimental results show that our scheme can effectively resist poisoning attacks, even if 50% of the fog nodes are contaminated by malicious clients. Moreover, the aggregation efficiency of the proposed scheme is improved by over 20%.

Easily Deployable and Efficiently Searchable Encryption (EDESE) is a cryptographic primitive designed for practical searchable applications, offering efficient search and easy deployment. However, it remains vulnerable to Leakage-Abuse attacks, allowing adversaries to exploit keyword-matching processes to extract sensitive information. To address these vulnerabilities, we introduce Leakage-Resilient EDESE (LR-EDESE) with k-indistinguishability and controlled leakage functions. We then propose Volume Leakage-Resilient EDESE (VLR-EDESE), a new scheme to protect against both query and document volume leakage. Our experimental results demonstrate that at k = 5000 (maximum security setting), VLR-EDESE incurs an overhead of 63× compared to the baseline EDESE without leakage protection, outperforming state-of-the-art methods with 320× and 97× overhead, respectively. For smaller k values (10, 20, 50, 100), storage and communication overhead remain within 2× and 2.5× of the baseline EDESE, highlighting VLR-EDESE's flexibility. Finally, we present CloudSec, an implementation of VLR-EDESE that seamlessly integrates with cloud storage platforms, using OneDrive as an example.

Abstract Policy-based chameleon hash (PCH) is a useful primitive in blockchain rewriting. It allows a party to compute a chameleon hash based on an access policy, and another party who possesses sufficient privileges satisfying the access policy to rewrite the hashed object. However, PCH lacks strong traceability. The chameleon trapdoor holder may abuse their rewriting privilege and maliciously rewrite the hashed object without being identified. In this paper, we introduce a new primitive called strongly traceable policy-based chameleon hash (STPCH for short). We first present a generic framework of STPCH. Then, we present a practical instantiation, show its practicality through implementation and evaluation analysis.

Abstract The World Wide Web Consortium (W3C) has established standards for decentralized identities (DIDs) and verifiable credentials (VCs). A DID serves as a unique identifier for an entity, while a VC validates specific attributes associated with the DID holder. To prove ownership of credentials, users generate verifiable presentations (VPs). To enhance privacy, the W3C standards advocate for randomizable signatures in VC creation and zero-knowledge proofs for VP generation. However, these standards face a significant limitation: they cannot effectively verify cross-domain credentials while maintaining anonymity. In this paper, we present Anonymous Verifiable Presentations with Extended Usability (AVPEU), a novel framework that addresses this limitation through the introduction of a notary system. At the technical core of AVPEU lies our proposed randomizable message-hiding signature scheme. We provide both a generic construction of AVPEU and specific implementations based on Boneh–Boyen–Shacham, Camenisch–Lysyanskaya, and Pointcheval–Sanders signature. Our experimental results demonstrate the feasibility of these schemes.

Blockchain rewriting is necessary for modifying illegal or invalid messages included in blockchain transactions, while maintaining the consistency of subsequent blocks in the blockchain. However, arbitrary blockchain rewriting is not desirable as it defeats the purpose of blockchain rewriting. In this work, we propose a new security primitive named message-controlled chameleon hash (MCH) and apply it for message control in blockchain rewriting to ensure that no unspecified messages are generated from blockchain rewriting. The proposed MCH enables permitted parties to select candidate messages from designated message sets for blockchain rewriting at the message level. Our evaluation shows that the performance of MCH is comparable to the classic CH [26] and the state-of-the-art CH [16]. We also show that the proposed MCH can be easily integrated into both permissioned and permissionless blockchains.

Chameleon hash (CH) function differs from a classical hash function in a way that a collision can be found with the knowledge of a trapdoor secret key. CH schemes have been used in various cryptographic applications such as sanitizable signatures and redactable blockchains. In this work, we reconstruct CH to ensure advanced security and usability. Our contributions are four-fold. First, we propose the first CH scheme, which supports full security, meaning the inclusion of both full indistinguishability and full collision-resistance. These two properties are required in the strongest CH security model in the literature. We achieve this by our innovative design of removing the CH public key during the computation of the hash value. Second, we investigate the security of CH in the multi-party setting and introduce the new properties of claimability and deniability under this setting. Third, we present and implement two instantiations of our CH scheme: an ECC-based one and a post-quantum lattice-based one. Our implementation demonstrates their practicality. Finally, we discuss the possible use cases in the blockchain.

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 schemes focus solely on message privacy. To address scenarios where attribute value information is also sensitive, Anonymous ABE (A2BE) ensures the privacy of both the message and attributes. However, most A2BE schemes suffer from intricate designs with low efficiency, and the security of the fastest key-policy A2BE (proposed in FEASE, USENIX'24) relies on the GGM.

With the development of vehicular networks and cloud-edge collaborative technologies, a large amount of vehicle data is collected at edge nodes (Edge Node, EN) for analysis and decision-making. However, edge data faces challenges in terms of integrity and security. Data owners (Data Owner, DO) should delegate auditors to periodically verify the integrity of the data. However, existing verification methods have not yet addressed issues related to verifiers forging evidence and fair payment. This paper proposes a smart contract-based edge data integrity verification scheme. An audit tree based on lattice hashing is designed, allowing the smart contract to initiate multiple verification challenges while only storing a complete label, thus reducing storage overhead. The homomorphic additivity of lattice hashing supports arbitrary data segmentation as challenges, effectively preventing EN from forging evidence. This scheme also designs two smart contract arbitration algorithms to ensure fair payment. Experimental comparisons show that this scheme effectively resolves the trust issues related to EN and ensures fair payment among EN, CSP, and DO.

Abstract Policy-based chameleon hash functions have been widely proposed for its use in blockchain rewriting systems. They allow anyone to create a mutable transaction associated with an access policy, while an authorized user who possesses sufficient rewriting privileges from a trusted authority satisfying the access policy can rewrite the mutable transaction. However, existing chameleon hash functions lack certain fundamental security guarantees, including forward security and backward security. In this paper, we introduce a new primitive called forward/backward-secure policy-based chameleon hash (FB-PCH for short). We present a practical instantiation. We prove that the proposed scheme achieves forward/backward-secure collision-resistance, and show its practicality through implementation and evaluation analysis.

Abstract In this paper, we introduce the first generic framework of policy-based remote user authentication from multiple biometrics. The proposed framework allows an authorized user to remotely authenticate herself to an authentication server using her multiple biometrics, which enhances both the security and usability of user authentications. The authentication server approves a user’s authentication request if and only if the user’s multiple biometrics satisfies an authentication policy. In particular, the authentication policy can be dynamically updated to satisfy different security and usability requirements in practice. We implement an instantiation of the proposed framework and report its performance under various authentication policies.

Blockchain rewriting with fine-grained access control allows a user to create a transaction associated with a set of attributes, while a modifier who possesses sufficient rewriting privileges from a trusted authority satisfying the attribute set can anonymously rewrite the transaction. However, it lacks accountability and is not designed for open blockchains that require no centralized trust authority. In this work, we introduce accountable fine-grained blockchain rewriting in a permissionless setting. The property of accountability allows the modifier’s identity and their rewriting privileges to be held accountable for the modified transactions in case of malicious rewriting. Our contributions are three-fold. First, we present a generic framework for secure blockchain rewriting in the permissionless setting. Second, we present an instantiation of our framework and show its practicality through evaluation analysis. Last, we demonstrate that our proof-of-concept implementation can be effectively integrated into open blockchains.

Abstract Policy-based chameleon hash is a useful primitive for blockchain rewriting systems. It allows a user to create a mutable transaction associated with an access policy, whereas a modifier who possesses sufficient rewriting privileges from a trusted authority satisfying the access policy can rewrite the mutable transaction. However, it lacks a revocation mechanism. The modifiers can always rewrite the mutable transactions even if their given rewriting privileges are compromised. In this work, we introduce revocable policy-based chameleon. The property of revocation allows some modifiers’ rewriting privileges to be revoked, regardless of whether their rewriting privileges are compromised or not.

Abstract Data owners often encrypt their bulk data and upload it to cloud in order to save storage while protecting privacy of their data at the same time. A data owner can allow a third-party entity to decrypt and access her data. However, if that entity wants to modify the data and publish the same in an authenticated way, she has to ask the owner for a signature on the modified data. This incurs substantial communication overhead if the data is modified often. In this work, we introduce the notion of policy-based editing-enabled signatures, where the data owner specifies a policy for her data such that only an entity satisfying this policy can decrypt the data. Moreover, the entity is permitted to produce a valid signature for the modified data (on behalf of the owner) without interacting with the owner every time the data is modified. On the other hand, a policy-based editing-enabled signature (PB-EES) scheme allows the data owner to choose any set of modification operations applicable to her data and still restricts a (possibly untrusted) entity to authenticate the data modified using operations from that set only. We provide two PB-EES constructions, a generic construction and a concrete instantiation. We formalize the security model for PB-EESs and analyze the security of our constructions. Finally, we evaluate the performance of the concrete PB-EES instantiation.

Abstract In this paper, we introduce a new construction for unlinkable secret handshake that allows a group of users to perform handshakes anonymously. We define formal security models for the proposed construction and prove that it can achieve session key security, anonymity and affiliation hiding. In particular, the proposed construction ensures that (i) anonymity against protocol participants (including group authority) is achieved since a hierarchical identity-based signature is used in generating group user’s pseudonym-credential pairs and (ii) revocation is achieved using a secret sharing-based revocation mechanism.

In this paper, we introduce a new construction of reusable fuzzy signature based remote user authentication that is secure against quantum computers. We investigate the reusability of fuzzy signature, and we prove that the fuzzy signature schemes provide biometrics reusability (aka. reusable fuzzy signature). We define formal security models for the proposed construction, and we prove that it achieves user authenticity and user privacy. The proposed construction ensures: 1) a user’s biometrics can be securely reused in remote user authentication; 2) a third party having access to the communication channel between a user and the authentication server cannot identify the user.

Distance-bounding protocol is a useful primitive in resisting distance-based attacks. Currently, most of the existing distance-bounding protocols usually do not take the reuse of nonces in designing the protocols into consideration. However, there have been some literature studies showing that nonce repetition may lead to the leakage of the shared key between protocol participants. Aikaterini et al. introduced a countermeasure that could serve as a supplementary in most distance-bounding systems allowing nonce repetition. However, their proposal only holds against passive attackers. In this paper, we introduce an active attack model and show that their countermeasure is insecure under the proposed active attack model. We also discover that all existing distance-bounding protocols with mutual authentication are vulnerable to distance-based attacks if a short nonce is applied under the proposed active model. To address this security concern, we propose a new distance-bounding protocol with mutual authentication to prevent distance-based attacks under the active adversary model. A detailed security analysis is presented for the proposed distance-bounding protocol with mutual authentication.

Policy-based chameleon hash is a useful primitive for blockchain rewriting. It allows a party to create a transaction associated with an access policy, while another party who possesses enough rewriting privileges satisfying the access policy can rewrite the transaction. However, it lacks accountability. The chameleon trapdoor holder may abuse his/her rewriting privilege and maliciously rewrite the hashed object in the transaction without being identified. In this paper, we introduce policy-based chameleon hash with black-box accountability (PCHBA). Black-box accountability allows an attribute authority to link modified transactions to responsible transaction modifiers in case of dispute, in which any public user identifies those transaction modifiers from interacting with an access device/blackbox. We first present a generic framework of PCHBA. Then, we present a practical instantiation, showing its practicality through implementation and evaluation analysis.

Cyber-Physical Systems (CPS) provide the foundation of our critical infrastructures, which form the basis of emerging and future smart services and improve our quality of life in many areas. In such CPS, sensor data is transmitted over the network to the controller, which will make real-time control decisions according to the received sensor data. Due to the existence of spoofing attacks (more specifically to CPS, false data injection attacks), one has to protect the authenticity and integrity of the transmitted data. For example, a digital signature can be used to solve this issue. However, the resource-constrained field devices like sensors cannot afford conventional signature computation. Thus, we have to seek for an efficient signature mechanism that can support the fast and continuous message authentication in CPS, while being easy to compute on the devices.

Abstract In this paper, we introduce a new construction for linkable secret handshake that allows authenticated users to perform handshake anonymously within allowable times. We define formal security models for the new construction, and prove that it can achieve session key security, anonymity, untraceability and linkable affiliation-hiding. In particular, the proposed construction ensures that (i) anyone can trace the real identities of dishonest users who perform handshakes for more than k times; and (ii) an optimal communication cost between authorized users is achieved by exploiting the proof of knowledges.

Data authentication primarily serves as a tool to achieve data integrity and source authentication. However, traditional data authentication does not fit well where an intermediate entity (editor) is required to modify the authenticated data provided by the source/data owner before sending the data to other recipients. To ask the data owner for authenticating each modified data can lead to higher communication overhead. In this article, we introduce the notion of editing-enabled signatures where the data owner can choose any set of modification operations applicable on the data and still can restrict any possibly untrusted editor to authenticate the data modified using an operation from this set only. Moreover, the editor does not need to interact with the data owner in order to authenticate the data every time it is modified. We construct an editing-enabled signature (EES) scheme that derives its efficiency from mostly lightweight cryptographic primitives. We formalize the security model for editing-enabled signatures and analyze the security of our EES scheme. Editing-enabled signatures can find numerous applications that involve generic editing tasks and privacy-preserving operations. We demonstrate how our EES scheme can be applied in two privacy-preserving applications.

In this paper, we introduce the first general framework for strong privacy-preserving biometric-based remote user authentication based on oblivious RAM (ORAM) protocol and computational fuzzy extractors. We define formal security models for the general framework, and we prove that it can achieve user authenticity and strong privacy. In particular, the general framework ensures that: (1) a strong privacy and a log-linear time-complexity are achieved by using a new tree-based ORAM protocol; (2) a constant bandwidth cost is achieved by exploiting computational fuzzy extractors in the challenge-response phase of remote user authentications.

Industrial Internet-of-Things (IIoT) is the basis of Industry 4.0, which extends Internet connectivity beyond traditional computing devices like computers and smartphones to the physical world for improving efficiency and accuracy while reducing the production cost. However, there are tremendous security threats to IIoT, such as IIoT device hijacking and data leaks. Therefore, a lightweight authenticated key agreement (AKA) protocol is commonly applied to establish a session key for securing the communication between IIoT devices. To protect the previous session keys from being compromised, perfect forward secrecy (PFS) has been one of the most important security properties of AKA. In this article, we present an efficient PFS-enabled AKA protocol for IIoT systems, which is developed based on a new dynamic authentication credential (DAC) framework, without using any public-key cryptographic primitives. It is worth noting that our protocol is also faster than the state-of-the-art DAC-based AKA protocols with PFS. Moreover, we give the formal security result of the proposed protocol in the random oracle model.

We introduce the first deniable attribute-based key exchange (DABKE) framework that is resilient to impersonation attacks. We define the formal security models for DABKE framework, and propose a generic compiler that converts any attribute-based key exchanges into deniable ones. We prove that it can achieve session key security and user privacy in the standard model, and strong deniability in the simulation-based paradigm. In particular, the proposed generic compiler ensures: 1) a dishonest user cannot impersonate other user’s session participation in conversations since implicit authentication is used among authorized users; 2) an authorized user can plausibly deny his/her participation after secure conversations with others; 3) the strongest form of deniability is achieved using one-round communication between two authorized users.

We introduce MobiCeal, the first practical Plausibly Deniable Encryption (PDE) system for mobile devices that can defend against strong coercive multi-snapshot adversaries, who may examine the storage medium of a user's mobile device at different points of time and force the user to decrypt data. MobiCeal relies on "dummy write" to obfuscate the differences between multiple snapshots of storage medium due to existence of hidden data. By incorporating PDE in block layer, MobiCeal supports a broad deployment of any block-based file systems on mobile devices. More importantly, MobiCeal is secure against side channel attacks which pose a serious threat to existing PDE schemes. A proof of concept implementation of MobiCeal is provided on an LG Nexus 4 Android phone using Android 4.2.2. It is shown that the performance of MobiCeal is significantly better than prior PDE systems against multi-snapshot adversaries.

Proxy signature is a useful cryptographic primitive that has been widely used in many applications. It has attracted a lot of attention since it was introduced. There have been lots of works in constructing efficient and secure proxy signature schemes. In this paper, we identify a new attack that has been neglected by many existing proven secure proxy signature schemes. We demonstrate this attack by launching it against an identity‐based proxy signature scheme which is proven secure. We then propose one method that can effectively prevent this attack. The weakness in some other proxy signature schemes can also be fixed by applying the same method.

Grouping proof is a very useful security primitive that can be used to prove the co-existence of multiple entities in an identification protocol. It can be incorporated into radio frequency identification protocols and used in many practical applications such as pharmaceutical distribution and manufacturing. However, the existing grouping proofs do not support secure key establishment, which is required in order to allow secure communication between the reader and the radio frequency identification tags after the identification process. In this paper, we propose a novel grouping proof with key exchange that allows the reader to establish a secure communication channel with the tags. We define the formal security models for grouping proof with key exchange and prove that the proposed generic protocol can achieve grouping proof soundness, session key security, contributiveness, and tag identity privacy.