Showing papers on "Verifiable secret sharing published in 2017"

Unconditionally verifiable blind quantum computation

Abstract: Blind quantum computing (BQC) allows a client to have a server carry out a quantum computation for them such that the client's input, output, and computation remain private. A desirable property for any BQC protocol is verification, whereby the client can verify with high probability whether the server has followed the instructions of the protocol or if there has been some deviation resulting in a corrupted output state. A verifiable BQC protocol can be viewed as an interactive proof system leading to consequences for complexity theory. We previously proposed [A. Broadbent, J. Fitzsimons, and E. Kashefi, in Proceedings of the 50th Annual Symposium on Foundations of Computer Science, Atlanta, 2009 (IEEE, Piscataway, 2009), p. 517] a universal and unconditionally secure BQC scheme where the client only needs to be able to prepare single qubits in separable states randomly chosen from a finite set and send them to the server, who has the balance of the required quantum computational resources. In this paper we extend that protocol with additional functionality allowing blind computational basis measurements, which we use to construct another verifiable BQC protocol based on a different class of resource states. We rigorously prove that the probability of failing to detect an incorrect output is exponentially small in a security parameter, while resource overhead remains polynomial in this parameter. This resource state allows entangling gates to be performed between arbitrary pairs of logical qubits with only constant overhead. This is a significant improvement on the original scheme, which required that all computations to be performed must first be put into a nearest-neighbor form, incurring linear overhead in the number of qubits. Such an improvement has important consequences for efficiency and fault-tolerance thresholds.

Unconditional security of entanglement-based continuous-variable quantum secret sharing

Abstract: The need for secrecy and security is essential in communication. Secret sharing is a conventional protocol to distribute a secret message to a group of parties, who cannot access it individually but need to cooperate in order to decode it. While several variants of this protocol have been investigated, including realizations using quantum systems, the security of quantum secret sharing schemes still remains unproven almost two decades after their original conception. Here we establish an unconditional security proof for entanglement-based continuous-variable quantum secret sharing schemes, in the limit of asymptotic keys and for an arbitrary number of players. We tackle the problem by resorting to the recently developed one-sided device-independent approach to quantum key distribution. We demonstrate theoretically the feasibility of our scheme, which can be implemented by Gaussian states and homodyne measurements, with no need for ideal single-photon sources or quantum memories. Our results contribute to validating quantum secret sharing as a viable primitive for quantum technologies.

NPP: A New Privacy-Aware Public Auditing Scheme for Cloud Data Sharing with Group Users

Abstract: Today, cloud storage becomes one of the critical services, because users can easily modify and share data with others in cloud. However, the integrity of shared cloud data is vulnerable to inevitable hardware faults, software failures or human errors. To ensure the integrity of the shared data, some schemes have been designed to allow public verifiers (i.e., third party auditors) to efficiently audit data integrity without retrieving the entire users’ data from cloud. Unfortunately, public auditing on the integrity of shared data may reveal data owners’ sensitive information to the third party auditor. In this paper, we propose a new privacy-aware public auditing mechanism for shared cloud data by constructing a homomorphic verifiable group signature. Unlike the existing solutions, our scheme requires at least t group managers to recover a trace key cooperatively, which eliminates the abuse of single-authority power and provides nonframeability. Moreover, our scheme ensures that group users can trace data changes through designated binary tree; and can recover the latest correct data block when the current data block is damaged. In addition, the formal security analysis and experimental results indicate that our scheme is provably secure and efficient.

SCRAPE: Scalable Randomness Attested by Public Entities

Abstract: Uniform randomness beacons whose output can be publicly attested to be unbiased are required in several cryptographic protocols. A common approach to building such beacons is having a number parties run a coin tossing protocol with guaranteed output delivery (so that adversaries cannot simply keep honest parties from obtaining randomness, consequently halting protocols that rely on it). However, current constructions face serious scalability issues due to high computational and communication overheads. We present a coin tossing protocol for an honest majority that allows for any entity to verify that an output was honestly generated by observing publicly available information (even after the execution is complete), while achieving both guaranteed output delivery and scalability. The main building block of our construction is the first Publicly Verifiable Secret Sharing scheme for threshold access structures that requires only O(n) exponentiations. Previous schemes required O(nt) exponentiations (where t is the threshold) from each of the parties involved, making them unfit for scalable distributed randomness generation, which requires \(t=n/2\) and thus \(O(n^2)\) exponentiations.

Minimizing latency for secure distributed computing

Abstract: We consider the setting of a master server who possesses confidential data (genomic, medical data, etc.) and wants to run intensive computations on it, as part of a machine learning algorithm for example. The master wants to distribute these computations to untrusted workers who have volunteered or are incentivized to help with this task. However, the data must be kept private (in an information theoretic sense) and not revealed to the individual workers. The workers may be busy and will take a random time to finish the task assigned to them. We are interested in reducing the aggregate delay experienced by the master. We focus on linear computations as an essential operation in many iterative algorithms. A known solution is to use a linear secret sharing scheme to divide the data into secret shares on which the workers can compute. We propose to use instead new secure codes, called Staircase codes, introduced previously by two of the authors. We study the delay induced by Staircase codes which is always less than that of secret sharing. The reason is that secret sharing schemes need to wait for the responses of a fixed fraction of the workers, whereas Staircase codes offer more flexibility in this respect. For instance, for codes with rate R = 1/2 Staircase codes can lead to up to 40% reduction in delay compared to secret sharing.

VKSE-MO: verifiable keyword search over encrypted data in multi-owner settings

Abstract: Searchable encryption (SE) techniques allow cloud clients to easily store data and search encrypted data in a privacy-preserving manner, where most of SE schemes treat the cloud server as honest-but-curious. However, in practice, the cloud server is a semi-honest-but-curious third-party, which only executes a fraction of search operations and returns a fraction of false search results to save its computational and bandwidth resources. Thus, it is important to provide a results verification method to guarantee the correctness of the search results. Existing SE schemes allow multiple data owners to upload different records to the cloud server, but these schemes have very high computational and storage overheads when applied in a different but more practical setting where each record is co-owned by multiple data owners. To address this problem, we develop a verifiable keyword search over encrypted data in multi-owner settings (VKSE-MO) scheme by exploiting the multisignatures technique. Thus, our scheme only requires a single index for each record and data users are assured of the correctness of the search results in challenging settings. Our formal security analysis proved that the VKSE-MO scheme is secure against a chosen-keyword attack under a random oracle model. In addition, our empirical study using a real-world dataset demonstrated the efficiency and feasibility of the proposed scheme in practice.

A Secure and Verifiable Outsourced Access Control Scheme in Fog-Cloud Computing.

Abstract: With the rapid development of big data and Internet of things (IOT), the number of networking devices and data volume are increasing dramatically. Fog computing, which extends cloud computing to the edge of the network can effectively solve the bottleneck problems of data transmission and data storage. However, security and privacy challenges are also arising in the fog-cloud computing environment. Ciphertext-policy attribute-based encryption (CP-ABE) can be adopted to realize data access control in fog-cloud computing systems. In this paper, we propose a verifiable outsourced multi-authority access control scheme, named VO-MAACS. In our construction, most encryption and decryption computations are outsourced to fog devices and the computation results can be verified by using our verification method. Meanwhile, to address the revocation issue, we design an efficient user and attribute revocation method for it. Finally, analysis and simulation results show that our scheme is both secure and highly efficient.

Verifiable Outsourced Decryption of Attribute-Based Encryption with Constant Ciphertext Length

Abstract: Outsourced decryption ABE system largely reduces the computation cost for users who intend to access the encrypted files stored in cloud. However, the correctness of the transformation ciphertext cannot be guaranteed because the user does not have the original ciphertext. Lai et al. provided an ABE scheme with verifiable outsourced decryption which helps the user to check whether the transformation done by the cloud is correct. In order to improve the computation performance and reduce communication overhead, we propose a new verifiable outsourcing scheme with constant ciphertext length. To be specific, our scheme achieves the following goals. Our scheme is verifiable which ensures that the user efficiently checks whether the transformation is done correctly by the CSP. The size of ciphertext and the number of expensive pairing operations are constant, which do not grow with the complexity of the access structure. The access structure in our scheme is AND gates on multivalued attributes and we prove our scheme is verifiable and it is secure against selectively chosen-plaintext attack in the standard model. We give some performance analysis which indicates that our scheme is adaptable for various limited bandwidth and computation-constrained devices, such as mobile phone.

Combination of Sharing Matrix and Image Encryption for Lossless $(k,n)$ -Secret Image Sharing

Abstract: This paper first introduces a $(k,n)$ -sharing matrix $S^{(k, n)}$ and its generation algorithm. Mathematical analysis is provided to show its potential for secret image sharing. Combining sharing matrix with image encryption, we further propose a lossless $(k,n)$ -secret image sharing scheme (SMIE-SIS). Only with no less than $k$ shares, all the ciphertext information and security key can be reconstructed, which results in a lossless recovery of original information. This can be proved by the correctness and security analysis. Performance evaluation and security analysis demonstrate that the proposed SMIE-SIS with arbitrary settings of $k$ and $n$ has at least five advantages: 1) it is able to fully recover the original image without any distortion; 2) it has much lower pixel expansion than many existing methods; 3) its computation cost is much lower than the polynomial-based secret image sharing methods; 4) it is able to verify and detect a fake share; and 5) even using the same original image with the same initial settings of parameters, every execution of SMIE-SIS is able to generate completely different secret shares that are unpredictable and non-repetitive. This property offers SMIE-SIS a high level of security to withstand many different attacks.

UnLynx: A Decentralized System for Privacy-Conscious Data Sharing

Abstract: Current solutions for privacy-preserving data sharing among multiple parties either depend on a centralized authority that must be trusted and provides only weakest-link security (e.g., the entity that manages private/secret cryptographic keys), or leverage on decentralized but impractical approaches (e.g., secure multi-party computation). When the data to be shared are of a sensitive nature and the number of data providers is high, these solutions are not appropriate. Therefore, we present UnLynx, a new decentralized system for efficient privacypreserving data sharing. We consider m servers that constitute a collective authority whose goal is to verifiably compute on data sent from n data providers. UnLynx guarantees the confidentiality, unlinkability between data providers and their data, privacy of the end result and the correctness of computations by the servers. Furthermore, to support differentially private queries, UnLynx can collectively add noise under encryption. All of this is achieved through a combination of a set of new distributed and secure protocols that are based on homomorphic cryptography, verifiable shuffling and zero-knowledge proofs. UnLynx is highly parallelizable and modular by design as it enables multiple security/privacy vs. runtime tradeoffs. Our evaluation shows that UnLynx can execute a secure survey on 400,000 personal data records containing 5 encrypted attributes, distributed over 20 independent databases, for a total of 2,000,000 ciphertexts, in 24 minutes.

Asymptotically Compact Adaptively Secure Lattice IBEs and Verifiable Random Functions via Generalized Partitioning Techniques.

Abstract: In this paper, we focus on the constructions of adaptively secure identity-based encryption (IBE) from lattices and verifiable random function (VRF) with large input spaces. Existing constructions of these primitives suffer from low efficiency, whereas their counterparts with weaker guarantees (IBEs with selective security and VRFs with small input spaces) are reasonably efficient. We try to fill these gaps by developing new partitioning techniques that can be performed with compact parameters and proposing new schemes based on the idea.

Message Franking via Committing Authenticated Encryption

Abstract: We initiate the study of message franking, recently introduced in Facebook’s end-to-end encrypted message system. It targets verifiable reporting of abusive messages to Facebook without compromising security guarantees. We capture the goals of message franking via a new cryptographic primitive: compactly committing authenticated encryption with associated data (AEAD). This is an AEAD scheme for which a small part of the ciphertext can be used as a cryptographic commitment to the message contents. Decryption provides, in addition to the message, a value that can be used to open the commitment. Security for franking mandates more than that required of traditional notions associated with commitment. Nevertheless, and despite the fact that AEAD schemes are in general not committing (compactly or otherwise), we prove that many in-use AEAD schemes can be used for message franking by using secret keys as openings. An implication of our results is the first proofs that several in-use symmetric encryption schemes are committing in the traditional sense. We also propose and analyze schemes that retain security even after openings are revealed to an adversary. One is a generalization of the scheme implicitly underlying Facebook’s message franking protocol, and another is a new construction that offers improved performance.

Computational Integrity with a Public Random String from Quasi-Linear PCPs

Abstract: A party executing a computation on behalf of others may benefit from misreporting its output. Cryptographic protocols that detect this can facilitate decentralized systems with stringent computational integrity requirements. For the computation’s result to be publicly trustworthy, it is moreover imperative to usepublicly verifiable protocols that have no “backdoors” or secret keys that enable forgery.

Verifiable outsourced ciphertext-policy attribute-based encryption in cloud computing

Abstract: In the attribute-based encryption (ABE) systems, users can encrypt and decrypt messages based on their attributes. Because of the flexibility of ABE, it is more and more widely used in various network environments. However, complex functionality of ABE may cause an enormous computational cost. This reason greatly restricts the application of ABE in practice. In order to minimize the local computation of ABE, we introduce the concept of verifiable outsourced ABE system, in which key generation center, encryptor and decryptor, are able to outsource their computing tasks to the corresponding service providers, respectively, to reduce the local load. In addition, they are also able to verify the correctness of outsourcing calculation efficiently by using the outsourcing verification services. This is useful to save local computational resources, especially for mobile devices. Then, we propose a specific verifiable outsourced ABE scheme and prove its adaptive security in the standard model using the dual-system encryption method. Finally, we introduce how to deploy our outsourced CP-ABE scheme in cloud computing environment.

Non-determinism in Byzantine Fault-Tolerant Replication

Abstract: Service replication distributes an application over many processes for tolerating faults, attacks, and misbehavior among a subset of the processes. With the recent interest in blockchain technologies, distributed execution of one logical application has become a prominent topic. The established state-machine replication paradigm inherently requires the application to be deterministic. This paper distinguishes three models for dealing with non-determinism in replicated services, where some processes are subject to faults and arbitrary behavior (so-called Byzantine faults): first, the modular case that does not require any changes to the potentially non-deterministic application (and neither access to its internal data); second, master-slave solutions, where ties are broken by a leader and the other processes validate the choices of the leader; and finally, applications that use cryptography and secret keys. Cryptographic operations and secrets must be treated specially because they require strong randomness to satisfy their goals. The paper also introduces two new protocols. First, Protocol Sieve uses the modular approach and filters out non-deterministic operations in an application. It ensures that all correct processes produce the same outputs and that their internal states do not diverge. A second protocol, called Mastercrypt, implements cryptographically secure randomness generation with a verifiable random function and is appropriate for most situations in which cryptographic secrets are involved. All protocols are described in a generic way and do not assume a particular implementation of the underlying consensus primitive.

Dynamic quantum secret sharing by using d-dimensional GHZ state

Abstract: Through generating the d-dimensional GHZ state in the Z-basis and measuring it in the X-basis, a dynamic quantum secret sharing scheme is proposed. In the proposed scheme, multiple participants can be added or deleted in one update period, and the shared secret does not need to be changed. The participants can be added or deleted by themselves, and the dealer does not need to be online. Compared to the existing schemes, the proposed scheme is more efficient and more practical.

Homomorphic Secret Sharing from Paillier Encryption

Abstract: A recent breakthrough by Boyle et al. [7] demonstrated secure function evaluation protocols for branching programs, where the communication complexity is sublinear in the size of the circuit (indeed just linear in the size of the inputs, and polynomial in the security parameter). Their result is based on the Decisional Diffie-Hellman assumption (DDH), using (variants of) the ElGamal cryptosystem. In this work, we extend their result to show a construction based on the circular security of the Paillier encryption scheme. We also offer a few optimizations to the scheme, including an alternative to the “Las Vegas”-style share conversion protocols of [7, 9] which directly checks the correctness of the computation. This allows us to reduce the number of required repetitions to achieve a desired overall error bound by a constant fraction for typical cases, and for large programs, reduces the total computation cost.

A Generic Approach to Constructing and Proving Verifiable Random Functions.

Abstract: Verifiable Random Functions (VRFs) as introduced by Micali, Rabin and Vadhan are a special form of Pseudo Random Functions (PRFs) wherein a secret key holder can also prove validity of the function evaluation relative to a statistically binding commitment.

A Generic Approach to Constructing and Proving Verifiable Random Functions.

Abstract: Verifiable Random Functions (VRFs) as introduced by Micali, Rabin and Vadhan are a special form of Pseudo Random Functions (PRFs) wherein a secret key holder can also prove validity of the function evaluation relative to a statistically binding commitment.

Verifiable Public Key Encryption Scheme With Equality Test in 5G Networks

Abstract: The emergence of 5G networks will allow cloud computing providers to offer more convenient services. However, security and privacy issues of cloud services in 5G networks represent huge challenges. Recently, to improve security and privacy, a novel primitive was proposed by Ma et al. in TIFS 2015, called public key encryption with equality test supporting flexible authorization (PKEET-FA). However, the PKEET scheme lacks verification for equality test results to check whether the cloud performed honestly. In this paper, we expand the study of PKEET-FA and propose a verifiable PKEET (V-PKEET) scheme, which, to the best of our knowledge, is the first work that achieves verification in PKEET. Moreover, V-PKEET has been designed for three types of authorization to dynamically protect the privacy of data owners. Therefore, it further strengthens security and privacy in 5G networks.

ExpSOS: Secure and Verifiable Outsourcing of Exponentiation Operations for Mobile Cloud Computing

Abstract: Discrete exponential operation, such as modular exponentiation and scalar multiplication on elliptic curves, is a basic operation of many public-key cryptosystems. However, the exponential operations are considered prohibitively expensive for resource-constrained mobile devices. In this paper, we address the problem of secure outsourcing of exponentiation operations to one single untrusted server. Our proposed secure outsourcing scheme for general exponential (ExpSOS) only requires a very limited number of modular multiplications at local mobile environment, and thus it can achieve significant computational performance gain. ExpSOS also provides a secure verification scheme with probability approximately 1 to ensure that the mobile end users can always receive valid results. The comprehensive analysis as well as the simulation results in real mobile device demonstrates that our proposed ExpSOS can significantly improve the existing schemes in efficiency, security, and result verifiability. We apply ExpSOS to securely outsource several cryptographic protocols to show that ExpSOS can be widely applied to many computation-intensive applications and achieve significant performance improvement.

An efficient (t,n)---threshold secret image sharing scheme

Abstract: We propose a novel (t,n)---threshold secret image sharing scheme based on Shamir's polynomial interpolation paradigm. The proposed scheme is a derivative of Thien and Lin's (Computers & Graphics 26(5):765---770, [13]) and some of its variants by ensuring less intrusive changes in the secret image. This is achieved by cyclically shifting the bits of the secret image, thus allowing a modification in the least significant bit to have a large effect on the values used in computation of shadow images. Statistical tests and simulations are presented to show the efficiency and robustness of the proposed scheme, in particular good randomness of shadow images, little correlation between adjacent pixels, and high entropy. Competence of the proposed scheme is further demonstrated by means of comparison with existing schemes.

An Efficient Lattice Based Multi-Stage Secret Sharing Scheme

Abstract: In this paper, we construct a lattice based threshold multi-stage secret sharing (MSSS) scheme according to Ajtai’s construction for one-way functions. In an MSSS scheme, the authorized subsets of participants can recover a subset of secrets at each stage while other secrets remain undisclosed. In this paper, each secret is a vector from a $t$ -dimensional lattice and the basis of each lattice is kept private. A $t$ -subset of $n$ participants can recover the secret(s) using their assigned shares. Using a lattice based one-way function, even after some secrets are revealed, the computational security of the unrecovered secrets is provided against quantum computers. The scheme is multi-use in the sense that to share a new set of secrets, it is sufficient to renew some public information such that a new share distribution is no longer required. Furthermore, the scheme is verifiable meaning that the participants can verify the shares received from the dealer and the recovered secrets from the combiner, using public information.

VeidBlock: Verifiable Identity using Blockchain and Ledger in a Software Defined Network

Abstract: Blockchain and verifiable identities have a lot of potential in future distributed software applications e.g. smart cities, eHealth, autonomous vehicles, networks, etc. In this paper, we proposed a novel technique, namely VeidBlock, to generate verifiable identities by following a reliable authentication process. These entities are managed by using the concepts of blockchain ledger and distributed through an advance mechanism to protect them against tampering. All identities created using VeidBlock approach are verifiable and anonymous therefore it preserves user's privacy in verification and authentication phase. As a proof of concept, we implemented and tested the VeidBlock protocols by integrating it in a SDN based infrastructure. Analysis of the test results yield that all components successfully and autonomously performed initial authentication and locally verified all the identities of connected components.

Asymptotically Compact Adaptively Secure Lattice IBEs and Verifiable Random Functions via Generalized Partitioning Techniques

Abstract: In this paper, we focus on the constructions of adaptively secure identity-based encryption (IBE) from lattices and verifiable random function (VRF) with large input spaces. Existing constructions of these primitives suffer from low efficiency, whereas their counterparts with weaker guarantees (IBEs with selective security and VRFs with small input spaces) are reasonably efficient. We try to fill these gaps by developing new partitioning techniques that can be performed with compact parameters and proposing new schemes based on the idea.

Hardening Distributed and Encrypted Keyword Search via Blockchain

Abstract: Distributed storage platforms draw much attention due to their high reliability and scalability for handling a massive amount of data. To protect user and data privacy, encryption is considered as a necessary feature for production systems like Storj. But it prohibits the nodes from performing content search. To preserve the functionality, we observe that a protocol of integration with searchable encryption and keyword search via distributed hash table allows the nodes in a network to search over encrypted and distributed data. However, this protocol does not address a practical threat in a fully distributed scenario. Malicious nodes would sabotage search results, and easily infiltrate the system as the network grows. Using primitives such as MAC and verifiable data structure may empower the users to verify the search result, but the robustness of the overall system can hardly be ensured. In this paper, we address this issue by proposing a protocol that is seamlessly incorporated to encrypted search in distributed network to attest and monitor nodes. From the moment a node joins the system, it will be attested and continuously monitored through verifiable search queries. The result of each attestation is determined via a standard quorum-based voting protocol, and then recorded on the blockchain as a consensus view of trusted nodes. Based on the proposed protocols, malicious nodes can be detected and removed by a majority of nodes in a self-determining manner. To demonstrate the security and efficiency, we conduct robustness analysis against several potential attacks, and perform performance and overhead evaluation on the proposed protocol.

SCRAPE: Scalable Randomness Attested by Public Entities.

Abstract: Uniform randomness beacons whose output can be publicly attested to be unbiased are required in several cryptographic protocols. A common approach to building such beacons is having a number parties run a coin tossing protocol with guaranteed output delivery (so that adversaries cannot simply keep honest parties from obtaining randomness, consequently halting protocols that rely on it). However, current constructions face serious scalability issues due to high computational and communication overheads. We present a coin tossing protocol for an honest majority that allows for any entity to verify that an output was honestly generated by observing publicly available information (even after the execution is complete), while achieving both guaranteed output delivery and scalability. The main building block of our construction is the first Publicly Verifiable Secret Sharing scheme for threshold access structures that requires only O(n) exponentiations. Previous schemes required O(nt) exponentiations (where t is the threshold) from each of the parties involved, making them unfit for scalable distributed randomness generation, which requires \(t=n/2\) and thus \(O(n^2)\) exponentiations.