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A multi-party quantum key distribution protocol based on repetitive code is designed for the first time in this paper. First we establish a classical (t, n) threshold protocol which can authenticate the identity of the participants, and encode the classical key sequence in accordance with this repetitive code. Then unitary transformation of the quantum state sequence corresponding to this encoded sequence is carried out by using the parameters from this (t, n) threshold protocol. Furthermore, we derive two thresholds for whether or not reserving the measured values of the received sequence, and extract the classical subkey sequence from the measured values conforming to these two threshold conditions. This protocol can authenticate the identity of the participant, resist the attack from the internal and external participants, and do not need the decoy state particles when testing the eavesdropper, which is more efficient than the similar protocols, and also saves the quantum resources.

In a data access control system oriented toward the cloud storage environment, a data owner defines attribute-based access control policies for data files to realize fine-grained data sharing. However, the existing schemes have defects in user execution efficiency and user privacy protection, and they do not consider the problems of user revocation and attribute updates. To this end, we propose a ciphertext policy attribute-based encryption method with verifiable outsourced decryption; this requires a user to complete decryption with the help of a server, but the results of the outsourced decryption can be verified independently. With this new encryption scheme and the technique of k-times anonymous authentication, a new fine-grained data access control system was constructed; this system allows a server to provide users with outsourced decryption services, and users’ computation cost is independent of the size of the underlying access control policy. Moreover, the number of outsourced decryption requests is limited. In addition, the new system supports user revocation and attribute updates and it is provably secure under formal proofs. An efficiency analysis shows that it can be compared with other similar systems in terms of performance, despite the addition of several practical properties.

We consider the verifiable problem of delegation computing in cloud, which means a client needs to outsource a computing function to untrusted servers, and verify the returned computational results. A recently related result of Dong et al. (CCS 2017) shows a client outsources the same computation task to two different servers, which achieves verifiability by simply cross-checking. In Dong’s replication-based scheme, although the expensive cryptographic algorithms for verification is not needed, the delegation overhead is double. In order to reduce delegation overhead of Dong’s scheme, we propose a novel incentive-compatible rational delegation computing scheme. Specifically, the client sends duplicate tasks to some servers for cross-checking, meanwhile, each sever only knows the probability distribution of receiving a duplicate task. Furthermore, considering rational delegation computing as a dynamic game with imperfect information , we design reasonable and effective incentive mechanisms. Afterwards, we seek a unique sequential equilibrium in each game, and strictly prove that rational players still have no motivation to deviate from honest behavior under a condition of lower delegation overhead. Detailed analysis indicates that the lowest delegation overhead achieved by our scheme is only n 2 n - 2 of that achieved by Dong’s scheme, where n means the number of servers.

Private Information Retrieval (PIR) allows a client to privately retrieve some data from a public database. There exist two types of PIR: (computational) Single-server PIR (SPIR) and (information-theoretic) multi-server PIR. In this paper, we focus on exploring SPIR. We first propose a simple and efficient additively-homomorphic encryption scheme of which privacy is based on the learning with binary errors assumption that is known as an interesting candidate for practical lattice-based cryptography. Then, according to our proposed homomorphic encryption scheme, we give a Verifiable (single/multi-bit) SPIR (VSPIR) scheme for the single-query case under the malicious server model. To the best of our knowledge, our proposal is the first practical non-interactive VSPIR scheme employing an efficient probabilistic proof that can discover the forged result with overwhelming probability. The corresponding communication complexity and computational complexity are comparable with those of some typical SPIR schemes. Moreover, we extend our single-query VSPIR scheme to construct a non-interactive multi-query solution. In particular, the corresponding communication complexity and computational complexity are the same as those of the single-query scheme. Finally, we provide detailed implementation results to confirm efficiency of our proposals.

As a novel problem-solving paradigm, crowdsourcing has been emerged aiming at performing truthful data aggregation and addressing problems that are hard for one organization. However, in reality, these answers submitted by distributed workers can be regarded as their intellectual properties because of professional skills and intensive computation overhead. Besides, it may contain highly sensitive information and should not be directly released without protection. Besides, the worker skill estimation is only considered into plaintext scenario but no longer suitable to ciphertext setting. To address these challenges, we propose a novel privacy-preserving and verifiable online crowdsourcing protocol (PVOC) for workers in the same group while preserving their answers privacy. Besides, PVOC also supports worker dynamic adding and revocation for different classification tasks with a minimum computation overhead. Finally, we introduce a verification mechanism to identify and update the worker skills of participants. Thus, since no decryption operations are involved in PVOC, our design is efficient and lightweight. Security analysis demonstrates that PVOC can guarantee the workers’ privacy without accuracy loss. Furthermore, we evaluate and show its effectiveness and practicability on three real datasets MNIST, CIFAR-10 and CIFAR-100.

For successful electronic voting (e-voting), it is critically important to ensure the security, privacy and verifiability of all steps. This paper uses Intel Software Guard Extensions (SGX) to achieve these goals and provide protection against malicious adversaries with administrative access. We introduce a Distributed SGX Networked System (DSGXNS). It connects one or several SGXs and the bulletin board of the election. We propose and investigate a DSGXNS-based secure, publicly verifiable and self-tallying online voting protocol. Each cast vote is uploaded to the DSGXNS via a secure communication channel built after a remote attestation. The validity of submissions is verified inside the SGX enclaves and legitimate votes are encrypted there. For end-to-end voter verification, a new encryption mechanism is proposed. It prevents confidentiality breaches and enables everyone to verify the validity of submissions and the outcome, which can be self-tallied using a homomorphic property. It maintains confidentiality because even the system administrators or malicious adversaries gaining administrative access cannot read data in the SGX enclaves. Every voter can verify all steps of the election and tally the cast ballots. Our theoretical analysis and experiments show that the protocol is secure and efficient.

A fair contract signing scheme ensures that contract signing participants can fairly exchange the digital signatures of the contract, which has a wide range of applications on the Internet. Verifiable Encrypted Signature (VES) can be used as a fair exchange mechanism for digital signatures, in which it requires a centralized Trusted Third Party (TTP) as an adjudicator. However, there are many security challenges with the centralized TTP. For example, it may disclose the contents of the contract, collude with others, or even occurs a service interruption. To address those problems, in this paper, we propose a two-party fair contract signing scheme based on Ethereum smart contract, which allows participants to fairly perform the contract signing procedures on the blockchain. Specifically, we propose a modified VES scheme in which no centralized adjudicator is needed. Then we design the fair contract signing scheme based on the modified VES scheme. We leverage the Ethereum smart contract technology to ensure fairness, which has the characteristics of decentralization, verifiability, autonomy, efficiency, and tampering resistant. The theoretical analysis and experimental results show that our scheme is secure and feasible.

With the rapid development of cloud computing, the practical applications such as the machine learning based on the outsourced data have been investigated in the data sharing setting. In machine learning, the inner product is a necessary primitive to analyze the description statistics. However, the inner product computation in selective data sharing setting has not been fully considered. For this fact, we propose a verifiable inner product computation scheme based on Inner Product Functional Encryption (IPFE). IPFE is employed to preserve the outsourced data privacy and restrict the computation on the outsourced data to be inner product. To achieve the key privacy and result privacy, we transform the secret key into blinded form, which in turn results in a blinded result. With the aim of implementing access control over the data user and outsourced data, we design to let cloud server perform the authentication procedures before computing inner product. This can also eliminate most computational overhead resulting from the unauthorized data user and undesired data. As a result, only the authorized data user can obtain the inner product computed on the designated outsourced data. The proposed scheme is proved to be secure under the authentication model and the result unforgeability model. The performance evaluation shows that the proposed scheme is feasible. To achieve a better security level, the proposed scheme is extended to be secure against the corrupted cloud server.

Based on a point-to-point quantum key distribution protocol and classical key distribution technologies, the concept of quantum-classical key and a new multi-party quantum-classical key agreement protocol is proposed in this paper. The distributor and any one of the participants use quantum key distribution protocol to negotiate subkey, then each of the participants shares his subkey with other participants using Shamir threshold secret sharing scheme, thus each participant will sort these subkeys and his own subkey in order, and eventually get this quantum-classical key. In this protocol, a pair of function values of binary polynomials are used to ensure the authentication of sub-shares and information among participants, and Lagrange interpolation formula of unary polynomials is used to ensure the recovery of subkeys. Security analysis shows that this protocol is secure, practical and effective.

Smart contracts allow verifiable operations to be executed in blockchains, bringing new possibilities for trust establishment in trustless scenarios. However, smart contracts are cumbersome when used as security mechanisms in security scenarios due to two reasons: they have limited power and are inert to changes. In order to mitigate the two problems of employed smart contracts, we propose LSC, a framework for online auto-update smart contracts in blockchain-based log systems, to enable self-adaptive log anomaly detection via smart contracts. Time-varying log anomaly detection patterns are extracted by self-adaptive machine learning log anomaly analysis and are continuously fed to the contracts. The framework allows smart contracts to be automatically updated to express the patterns in low-cost ways. The anomaly detection strategies for audit log systems are shared and collaboratively enforced amongst network nodes to defend against targeted detection evasion. We provide a plain prototype as a proof of the feasibility and efficiency of LSC in log systems.

The generalized compact knapsack function is defined as f a ( x ) = ∑ i a i . x i , where a = ( a 1 , … , a m ) ∈ R for some ring R and x = ( x 1 , … , x m ) ∈ S for a specified subset S ⊂ R. It is known that, for appropriate choice of R and S , inverting this function is at least as hard as solving certain worst-case problems on cyclic lattices . In this paper, we exploit collision-resistance as well as homomorphic properties of this function to propose a threshold verifiable secret sharing scheme with two distinguished features: first, the security of the scheme is completely based on lattice problems and second, upon receiving shares, participants can verify consistency of their shares with the secret without any communication.

The notion of a Designated Verifier Signature (DVS) scheme allows a signer to create a signature which is only verifiable by an intended verifier. DVS is a very useful scheme for authenticating a signer without interfering with her privacy. In 2003, Steinfeld et al. extended this notion to enable a Universal Designated Verifier Signature (UDVS) scheme. In UDVS, everyone who holds Alice’s traditional signature on a message (the signature holder), can transform it into a DVS for a specific verifier. Non-delegatability is a critical property of a DVS scheme in applications where responsibility of a signer is important and can not be delegated to another entity. Shim (Information Science, 2014) posed an open problem on how to construct a non-delegatable UDVS scheme. Since then, it has been well acknowledged that constructing a UDVS scheme which is non-delegatable remains as an elusive research problem. Furthermore, gaining a construction which is based on the standard model (without random oracles) is most desirable in practice. In this work, we present an affirmative answer to the aforementioned open research problem. We present the first non-delegatable UDVS scheme and prove its security requirements in the standard model. To the best of our knowledge, our work is the first non-delegatable UDVS scheme, which fills the gap in the existing literature. Furthermore, when the signer is considered as the signature holder, our scheme is also considered as the first non-delegatable DVS scheme in the standard model.

Cloud storage allows customers to store their data on remote cloud servers. With the advantage of reducing the burden of data management and storage, an increasing number of users prefer to store their data on the cloud. While secure data deletion is a crucial, it is a challenging issue in cloud storage. Logically deleted data may be easily exposed to un-authorized users in the cloud storage scenario thanks to its salient features such as multi-tenancy, virtualization and elasticity . Moreover, cloud servers might not delete customers’ data as instructed for hidden business interest. Hence, assured deletion is highly sought after. It helps preserve cloud users’ data privacy and is a necessary component of data retention regulations in cloud storage. In this paper, we first investigate the goals of assured data deletion and formalize its security model.Then, we propose a key-policy attribute-based encryption scheme for assured deletion (AD-KP-ABE) of cloud data. Our construction makes use of the attribute revocation cryptographic primitive and Merkle Hash Tree to achieve fine-grained access control and verifiable data deletion. The proposed AD-KP-ABE enjoys desirable properties such as no secret key update, partial ciphertext update and assured data deletion. The detailed security proof and implementation results demonstrate the security and practicality of our proposal.

In recent years, cloud computing has become the most popular and promising service platform. A cloud user can outsource its heavy computation overhead to a cloud service provider (CSP) and let the CSP make the computation instead. In order to guarantee the correctness of the outsourced processing (e.g., machine learning and data mining), a proof should be provided by the CSP in order to make sure that the processing is carried out properly. On the other hand, from the security and privacy points of view, users will always encrypt their sensitive data first before they are outsourced to the CSP rather than sending the raw data directly. However, processing and verifying of encrypted data computation has always been a challenging problem. Homomorphic Encryption (HE) has been proposed to tackle this task on computations over encrypted data and ensure the confidentiality of the data. However, original HE cannot provide an efficient approach to verify the correctness of computation over encrypted data that is processed by CSP. In this paper, we propose a verifiable outsourced computation scheme over encrypted data with the help of fully homomorphic encryption and polynomial factorization algorithm . Our scheme protects user data security in outsourced processing and allows public verification on the computation result processed by CSP with zero knowledge. We then prove the security of our scheme and analyze its performance by comparing it with some latest related works. Performances analysis shows that our scheme reduces the overload of both the cloud users and the verifier.

Searchable Encryption (SE) enables a user to search over encrypted data, such as data stored in a remote cloud server. Existing certificate-, identity-, and attribute-based SE schemes suffer from certificate management or key escrow limitations. Furthermore, the semi-honest-but-curious cloud may conduct partial search operations and return a fraction of the search results (i.e., incomplete results) in order to reduce costs. In this paper, we present a secure cryptographic primitive, Verifiable Multiple Keywords Search (VMKS) over ciphertexts, which leverages the Identity-Based Encryption (IBE) and certificateless signature techniques. The VMKS scheme allows the user to verify the correctness of search results and avoids both certificate management or key escrow limitations. We then demonstrate the security of proposed VMKS scheme (i.e., the scheme achieves both ciphertext indistinguishability and signature unforgeability). We also use a real-world dataset to evaluate its feasibility and efficiency.

Access control encryption (ACE), as a new cryptographic framework was proposed by Damgard et al. (at TCC 2016), enables controlling both the writing users and the reading users. Recently, a number of access control encryptions are proposed, but none of them are able to implement the verifiability of the sanitized ciphertexts which may lead to incorrect decryption. To solve this problem, by adapting Kim and Wu’s techniques (at ASIACRYPT 2017) and combining with the strong randomness extractor, we put forward a generic framework of access control encryption with verifiable sanitized decryption for arbitrary policy. The instantiabilities of the used building blocks from standard assumptions illustrates that our new construction works well. Moreover, we prove that our scheme not only satisfies the standard security definitions of access control encryption but also achieves the verifiability security for the sanitized ciphertexts.

To reduce the vulnerability of the multimedia content against the wide attacking surface of the cloud-based paradigm, obscuring the information before dissemination becomes a necessary step. In this paper, a reversible data hiding scheme based on Shamirs secret sharing for rightful ownership verification in encrypted domain has been proposed. It obscures the cover information via distributing it into multiple random looking shares and embeds a secret information specific to the owner into some of these encrypted shares based on a secret key prior to outsourcing the media information to cloud servers. The shares reveal no information at the cloud servers and even if they get attacked at these cloud servers, the owner information can be extracted to provide the rightful ownership of the media. The scheme facilitates extraction of secret information either directly from the cloud servers or after recovery of the original media at the authentic entity end possessing the secret keys. The robustness of the scheme has been validated by considering different attack scenarios in the encrypted domain itself. The visual quality of the recovered media and the extracted secret information evaluated via peak signal to noise ratio (PSNR), normalized cross correlation metric (NCC) and structural similarity index (SSIM) prove the efficacy of the proposed scheme.

With the prevalence of the cloud computing, data owners can outsource their data to the cloud server to enjoy convenient services. To ensure the user's data confidentiality, the outsourced data are usually stored in an encryption form on the cloud server, which makes it extremely difficult to search the specific encrypted documents matching some keywords from the cloud server for users. To address this issue, in this paper, we develop a multi-keyword ranked search scheme over encrypted cloud data, which also supports search results verification. To achieve efficient multi-keyword search, we construct a special data structure QSet based on an inverted index structure. To reduce the search complexity, we use the strategy that firstly searching the estimated least frequent keyword in the query to significantly narrow down the number of searching documents. Within this framework, to support ranked search, we utilize the common TFIDF rule to compute the relevance scores of documents matching a given search request. To resist malicious behaviors of the cloud server, we generate a binary vector for each keyword and use MAC to check the authenticity of the returned ciphertexts. The security analysis demonstrates that our proposed schemes are semantic secure in the adaptive setting. Extensive experimental evaluation shows the efficiency in the computation overhead of search and verification.

A publicly verifiable secret sharing allows anyone to detect the cheating of dealer or participants only from the public information. In this paper, by using bilinear pairings and monotone span programs we propose two practical publicly verifiable secret sharing schemes with general access structure. The first scheme has provable security in the standard model. The other scheme is proactive, robust and secure against mobile attack. These schemes tolerate active and adaptive adversaries and provide great capabilities for many applications.

Secret sharing (SS) is one of the most important cryptographic primitives used for data outsourcing. The (t, n) SS was introduced by Shamir and Blakley separately in 1979. The secret sharing policy of the (t, n) threshold SS is far too simple for many applications because it assumes that every shareholder has equal privilege to the secret or every shareholder is equally trusted. Ito et al. introduced the concept of a general secret sharing scheme (GSS). In a GSS, a secret is divided among a set of shareholders in such a way that any "qualified" subset of shareholders can access the secret, but any "unqualified" subset of shareholders cannot access the secret. The secret access structure of GSS is far more flexible than threshold SS. In this paper, we propose an optimized implementation of GSS. Our proposed scheme first uses Boolean logic to derive two important subsets, one is called Min which is the minimal positive access subset and the other is called Max which is the maximal negative access subset, of a given general secret sharing structure. Then, conditions of parameters of a GSS are established based on these two important subsets. Furthermore, integer linear/non-linear programming is used to optimize the size of shares of a GSS. The complexity of linear/non-linear programming is O(n), where n is the number of shares generated by the dealer. This proposed design can be applied to implement GSS based on any classical SS. However, our proposed method is limited to be applicable to some general secret sharing policies. We use two GSSs, one is based on Shamir's weighted SS (WSS) using linear polynomial and the other is based on Asmuth-Bloom's SS using Chinese Remainder Theorem (CRT), to demonstrate our design. In comparing with existing GSSs, our proposed scheme is more efficient and can be applied to all classical SSs.

Database as a Service (DBaaS) economically enables the customers with limited resources to outsource large-scale databases to the cloud. However, it becomes a very challenging problem that how to execute SQL on outsourced databases while protecting the confidentiality of outsourced databases at the same time. In this paper, we present a novel protocol to enable secure and efficient database outsourcing. First, we propose a new cloud database model by introducing computation service providers (CSPs), which can accommodate the conventional DBaaS model; the CSPs undertake most of the postprocessing and reconstruction burden for database query. Next, we design our database outsourcing protocol SecureDBS by leveraging a secret sharing mechanism and a novel tree-based order-preserving encryption (OPE) mechanism. The proposed protocol supports various SQL queries, including selection, update, insertion, and aggregate queries. Further, we present a mechanism to detect malicious behaviors of the cloud. Finally, we theoretically show that our protocol is correct, secure and efficient, and experimentally demonstrate that the protocol is efficient for practical usage.

In this paper, we propose a new type of digital signatures which is specifically designed for graph-based big data system. The properties of the proposed signatures are twofold. On one side it possesses the features of transitive signatures: One can sign a graph in such a way that, given two signatures on adjacent edges ( i , j ) and ( j , k ) , anyone with public information can compute a signature on edge ( i , k ) . The efficiency advancement ( O ( 1 ) communication overhead) in transitive signatures is especially important in big data paradigm. On the other side, it is universal designated verifiable: It allows any signature holder to prove to a designated verifier that a message has been signed by the signer, but the verifier cannot convince (even sharing all secret information) any other third party of this fact. The new notion is called Universal Designated Verifier Transitive Signatures ( UDVTS for short). As an integration of transitive signatures and universal designated verifier signatures, UDVTS can efficiently address privacy issues associated with dissemination of transitive signatures of graph-based big data. We further prove that our proposed design is secure in the random oracle model.

A new VC scheme with cheating-prevention ability is proposed.It reveals solid pattern with moderate-scale on partial-superimposed image.The proposed method verifies shares without any additional authentication shares.The proposed method endows conventional VC with cheating-prevention ability. This paper proposes a simple method for establishing a visual cryptographic (VC) scheme with the ability to prevent cheating. Given the n base-shares generated in a conventional (t,n), 2≤t≤n, VC scheme, an authentication pattern stamping process was designed to encode the n base-shares to get n verifiable shares that exhibit the following properties: (1) knowledge of less than t verifiable-shares gets no secret information, (2) the secret can be revealed by completely superimposing t or more verifiable-shares, and (3) the authentication pattern can be revealed by partially superimposing any pair of verifiable-shares. Theoretical proof and computer simulation for the proposed method are provided. The proposed method has smaller pixel expansion than previous cheating prevention VC schemes, and the verification process is fulfilled without resorting to any additional dedicated verification share. It can be attached easily to any reported VC scheme to endow legitimate users with the capability of detecting faked shares provided by malicious participants.

We shall propose two new efficient verifiable multi-secret sharing schemes based on linear feedback shift register (LFSR) public key and new nonhomogeneous linear recursions. Compared with previous schemes, these schemes have better performance and shorter private/public key length. Moreover, they have fewer public values and simpler construction, as well as various methods for the reconstruction phase. Altogether, they are easy to use and provide great capabilities for many applications.

Attribute-based encryption (ABE) enables an access control mechanism by specifying access control policies among decryption keys and ciphertexts. In this paper, we propose a novel ABE variant, dubbed directly revocable key-policyABEwith verifiable ciphertext delegation (drvuKPABE), which supports direct revocation and verifiable ciphertext delegation. The drvuKPABE offers the following features which are promising in the data sharing applications: (1) it allows the trusted authority to revoke users by solely updating the revocation list while mitigating the interaction with non-revoked users, which is unlikely to indirectly revokable ABE; (2) it allows the third party to update ciphertexts with public information so that those non-revoked users cannot decrypt them; and (3) it enables any auditor (authorized by data owners) to verify whether the untrusted third party updated ciphertexts correctly or not. We formalize the syntax and security properties for drvuKPABE, and propose the construction based on the multilinear maps. Our solution attains the security properties under the ( d + 3 ) -Multilinear Decisional Diffie-Hellman assumption in the random oracle model.

A verifiable ( k , t , n ) multi-secret sharing scheme (VMSS) allows a dealer to share k secrets among n players. In particular, (1) the secret shadow given by the dealer or some player can be verifiable and (2) t or more players can cooperate to reveal the k secrets, while less than t players cannot reveal any secret. VMSS can be used in many applications, such as access control. However, the existing VMSS schemes either require costly computation, or miss some important properties of VMSS. These two weaknesses make the VMSS scheme not so good as expected. In this paper, we propose a novel VMSS scheme which does not need any costly computation, while holds all properties of VMSS.

This paper presents a document protection scheme that integrates secret sharing and steganography. The secret document is divided into n shares based on a k − 1 degree polynomial, and the sharing scheme is tied in with a cover document. With the corresponding cover document, we can recover the secret by gathering at least k shares. To ensure each share is distinct, this work designs a method to avoid duplicate arguments of the polynomial. The security in the proposed scheme comes from two sides, secret sharing and steganography. The cover document is not restricted to the secret, hence our scheme is more flexible in choosing the cover document compared to other researchers’ schemes. Besides, the proposed scheme is easy to implement a hierarchical right management. Finally, experimental results and computational and security analysis are given to show that the proposed scheme is secure and practical.

Two extensions of RST (Rivest, Shamir and Taumann) ring signature are proposed which keep the form of RST ring signature unchanged. One extension is to implement the verifiability property with which the real signer is able to prove that she actually signed the ring signature if she publishes her secret value. In contrast to the available verifiable ring signatures, this scheme is very simple, secure and efficient. In this scheme only the glue value of RST ring signature is replaced by the output of a hash function which takes as input a secret value and some signature parameters and the real signer is able to prove himself any times. The other extension is to construct an anonymous subliminal channel in RST ring signature so that the subliminal sender (the real signer) is able to keep herself subliminal anonymous to the subliminal receiver. The subliminal anonymity is implemented for the first time in this paper. In addition, if the sender wants to revoke the subliminal anonymity, she is able to use the first extension.

Visual secret sharing (VSS) can encode a secret image into several share images where the original secret can be reconstructed and recognized by sight by stacking all share images. There are two categories of VSS schemes: visual cryptography (VC) and random grids (RG). VC has three main drawbacks: the large size, the need for the codebook to be redesigned for specific applications, and the ability to encode only one secret image at a time. RG removes the first two drawbacks. This paper proposes a novel RG-based VSS scheme that encodes multiple secret images at a time. The scheme encrypts multiple secret images into two circular cipher-grids and decrypts the images by stacking two circular cipher-grids to obtain the first secret and gradually rotating one circular cipher-grid at a fixed degree (based on the quantity of the secret images encrypted) to disclose other secrets. Compared with conventional VC-based VSS, the proposed scheme has no pixel expansion, a higher capacity for secret sharing, and no need for a complex VC codebook to be redesigned. Theoretical analysis of visual quality and security is demonstrated.

The secret sharing schemes in conventional visual cryptography are capable of sharing one secret image into a set of random transparencies (called shares) in the form of rectangles, which reveal the secret image to the human visual system when they are superimposed. Recently, visual secret sharing schemes involving multiple secrets have attracted much attention. By adopting rotations on one of the two encoded circle shares, more than two secrets could be shared. Yet, the encoding and decoding processes of circle shares need more sophisticated mechanisms than those of rectangular or square ones. In this paper, we explore the possibilities of visual multiple secret sharing using simply two rectangular or square shares. Specifically, we define some operations onto a transparency based upon turning over or flipping around. Then we propose visual cryptographic schemes that are able to encode two or four secrets into two rectangular shares and up to eight secrets into two square shares such that the secrets cannot be obtained from any single share, whereas they are revealed by stacking the two shares under various combinations of turning or flipping operations. The proposed schemes, which solidly elaborate the relationship between the encoded shares and the shared secrets, broaden the research scope and enrich the flexibility and applicability of visual cryptography or image encryption theoretically and practically.

Lin and Tasi, Yang et al., and Chang et al.'s meaningful secret sharing schemes provided authentication mechanisms but none included a remedy ability that would cause the secret image never to be completely obtained while some information of the stego-images are losing or tampering with. This paper proposes a meaningful secret-sharing scheme which includes both authentication and remedy abilities that allow for detection of the corrupted area and use of the hidden information to repair the secret image with reasonable visual quality. In comparison with previous schemes, this approach results in superior visual qualities of the stego-images by an average of more than 3dB.

A multi-secret sharing scheme is a protocol to share m arbitrarily related secrets s"1,...,s"m among a set of n participants. In this paper, we propose an ideal linear multi-secret sharing scheme, based on monotone span programs, where each subset of the set of participants may have the associated secret. Our scheme can be used to meet the security requirement in practical applications, such as secure group communication and privacy preserving data mining etc. We also prove that our proposed scheme satisfies the definition of a perfect multi-secret sharing scheme.

This paper presents a k-threshold computational secret sharing technique that distributes a secret S into shares of size |S|k-1, where |S| denotes the secret size. This bound is close to the space optimal bound of |S|k if the secret is to be recovered from k shares. In other words, our technique can be looked upon as a new information dispersal scheme that provides near optimal space efficiency. The proposed scheme makes use of repeated polynomial interpolation and has potential applications in secure information dispersal on the Web and in sensor networks.

A (t,n) threshold signature scheme allows t or more group members to generate signatures on behalf of a group with n members. In contrast to the traditional public key cryptography based on public key infrastructure (PKI) and identity-based public key cryptography (ID-PKC), certificateless public key cryptography (CL-PKC) offers useful properties as it does not require any certificates to ensure the authenticity of public keys and the key escrow problem is eliminated. In this paper, we investigate the notion of threshold signature schemes in CL-PKC. We start by pointing out the drawbacks in the two existing certificateless threshold signature schemes. Subsequently, we present an elaborate description of a generic certificateless (t,n) threshold signature scheme with a new security model. The adversaries captured in the new model are more powerful than those considered in the existing schemes. Furthermore, we establish the simulatability for certificateless threshold signature schemes and prove the relationship between the security of certificateless threshold signature schemes and that of the underlying non-threshold certificateless signature schemes. As an instantiation, we present a concrete certificateless threshold signature scheme based on bilinear maps using the techniques of verifiable secret sharing and distributed key generation. The proposed scheme is shown to be existentially unforgeable against adaptively chosen message attacks assuming the hardness of Computational Diffie-Hellman (CDH) problem.

A (t,n) secret sharing divides a secret into n shares in such a way that any t or more than t shares can reconstruct the secret; but fewer than t shares cannot reconstruct the secret. In this paper, we extend the idea of a (t,n) secret sharing scheme and give a formal definition on the (n,t,n) secret sharing scheme based on Pedersen's (t,n) secret sharing scheme. We will show that the (t,n) verifiable secret sharing (VSS) scheme proposed by Benaloh can only ensure that all shares are t-consistent (i.e. any subset of t shares defines the same secret); but shares may not satisfy the security requirements of a (t,n) secret sharing scheme. Then, we introduce new notions of strong t-consistency and strong VSS. A strong VSS can ensure that (a) all shares are t-consistent, and (b) all shares satisfy the security requirements of a secret sharing scheme. We propose a strong (n,t,n) VSS based on Benaloh's VSS. We also prove that our proposed (n,t,n) VSS satisfies the definition of a strong VSS.

In this paper, we propose a verifiable (t,n)-threshold multi-secret sharing scheme, based on one-dimensional cellular automata where the number of secrets is not restricted by n or t. We show that our scheme can be used to solve an open problem proposed recently in Alvarez et al. (2008) [G. Alvarez, L. Hernandez Encinas, A. Martin del Rey, A multisecret sharing scheme for color images based on cellular automata, Information Sciences 178 (2008) 4382-4395].

In 2006, Zhao et al. proposed a practical verifiable multi-secret sharing based on Yang et al.'s and Feldman's schemes. In this paper we propose two efficient, computationally secure (t,n), and verifiable multi-secret sharing schemes based on homogeneous linear recursion. The first scheme has the advantage of better performance, a new simple construction and various techniques for the reconstruction phase. The second scheme requires fewer public values with respect to Zhao et al.'s and Shao and Cao schemes. These schemes are easy to implement and provide great capabilities for many applications.

CRT-based threshold secret sharing schemes use sequences of pairwise co-prime positive integers in their construction. If these sequences are not ''compact'', then the CRT-based threshold secret sharing schemes may have a weak security in the sense of a massive loss of entropy or an arbitrarily large information rate. In this paper, compact sequences of co-primes are introduced, and their applications to the security of CRT-based threshold secret sharing schemes is throughout investigated. It is shown that all the results regarding the security of CRT-based threshold secret sharing schemes that use sequences of consecutive primes also hold for threshold secret sharing schemes that use compact sequences of co-primes. Moreover, compact sequences of co-primes may be significantly denser than sequences of consecutive primes of the same length, and their use in the construction of CRT-based threshold secret sharing schemes may lead to better security properties.