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Quantum secret sharing (QSS) is a fundamental primitive in quantum cryptography. The existing QSS protocols are either (n,n)-threshold or (t,n)-threshold access structure, where n denotes the number of players and t denotes the threshold number of players. Here, we introduce a novel verifiable QSS scheme that executes a restricted hyperstar access structure by using entangled states. Our method involves encoding selected quantum states and their corresponding measurements to yield outcomes of either + 1 or − 1. Furthermore, we give the validation of the scheme through the system of equations derived from the measurements, which then guarantees the honesty of the participants. At last, we also analyze the security of our scheme in two primary quantum attacks, such as external attacks and internal attacks. [ABSTRACT FROM AUTHOR]

There are perfect and ideal threshold secret sharing schemes, for example, Shamir’s secret sharing scheme. For the case of general secret sharing schemes with an arbitrary access structure, it is possible to construct a perfect scheme for any access structure (for example, the Ito – Saito – Nishizeki scheme, the Benaloh – Leichter scheme), but in general, such a scheme will not be an ideal secret sharing scheme. In the paper, for some classes of access structures, the construction of perfect and ideal secret sharing schemes based on linear codes is given. We also give a construction of perfect verifiable secret sharing schemes for any access structure for which there is a line code that implements this structure.

Sharing confidential information is a critical concern in today's world. Secret sharing schemes facilitate the sharing of secrets in a way that ensures only authorized participants (shareholders) can access the secret using their allocated shares. Hierarchical secret sharing schemes (HSSSs) build upon Shamir's scheme by organizing participants into different levels based on priority. Within HSSS, participants at each level can reconstruct the secret if a specified number, denoted as the threshold value (t), or more of them are present. Each level has a predetermined threshold value. If the number of participants falls below the threshold at any level, higher-level participants must be involved in reconstructing the secret at lower levels. Our paper proposes schemes that implement hierarchical access structures and enable the sharing of multiple secrets. Additionally, our proposed scheme includes share verification. We have analyzed potential attacks and demonstrated the scheme's resistance against them. Through security analysis and comparison with existing schemes, we highlight the novelty and superiority of our proposed approach, contributing to advancements in secure information-sharing practices. [ABSTRACT FROM AUTHOR]

The modern medical system is convergence of cutting-edge technologies and advancements in the healthcare environment. In the modern medical system, the storage of electronic health records is generally leased out to third-party cloud service providers (CSPs). But, CSPs cannot be entirely relied upon due to the potential security and privacy issues. This article presents Multi-Authority and Hierarchical Attribute-Based Encryption Scheme (MH-ABE) scheme to promote secure information sharing and protect patient's privacy. The utilization of CP-ABE in conjunction with multiple Attribute Authorities within the proposed MH-ABE scheme presents a scalable and fine-grained approach to data access control. The proposed MH-ABE scheme incorporates the utilization of a Hierarchical Access Tree to effectively encrypt numerous files concurrently, hence reducing the computational and storage cost. The proposed scheme has also been evaluated using a comparative analysis with existing schemes, emphasizing the assessment of computational and storage costs. The findings of this analysis demonstrate improved performance and efficiency of the proposed ciphertext policy based encryption scheme. The proposed MH-ABE scheme incorporates features such as policy hiding and revocation, and it exhibits resilience against attacks, including collusion resistance, Indistinguishability under chosen-plaintext attack and forward secrecy. [ABSTRACT FROM AUTHOR]

—In order to provide access control on encrypted data, Attribute-based encryption (ABE) defines each user using a set of attributes. Fuzzy identity-based encryption (FIBE) is a variant of ABE that allows for a threshold access structure for users. To address the potential threat posed by future quantum computers, this paper presents a postquantum fuzzy IBE scheme based on lattices. However, current lattice-based ABE schemes face challenges related to computational complexity and the length of ciphertext and keys. This paper aims to improve the performance of an existing fuzzy IBE scheme by reducing key length and computational complexity during the encryption phase. While negative attributes are not utilized in our scheme, we prove its security under the learning with error (LWE) hard problem assumption in the selective security model. These improvements have significant implications for the field of ABE.

In this paper, we propose a novel verifiable quantum secret sharing scheme tailored for a specific class of low-density parity-check (LDPC) codes. In the proposed protocol, Alice, the dealer, initially utilizes the generator matrix of the chosen LDPC code to calculate all secret shares and distributes individual shares to all participants in a quantum secure direct communication channel. In the distribution phase, each participant computes a hash value based on their respective share and a randomly generated sequence, which is then published. In the recover phase, each participant performs a unitary operation on these received particles and sends them to the next participant using the decoy-photon technique. Furthermore, the last participant performs Bell measurements on the final quantum states to obtain the original secret. At last, we demonstrate our protocol to be secure against intercept-and-resend attack, entangle-and-measure attack and dishonest participant attack. In addition, we present a comparison of our protocol with other existing schemes. [ABSTRACT FROM AUTHOR]

In order to provide access control on encrypted data, Attribute-based encryption (ABE) defines each user using a set of attributes. Fuzzy identity-based encryption (FIBE) is a variant of ABE that allows for a threshold access structure for users. To address the potential threat posed by future quantum computers, this paper presents a postquantum fuzzy IBE scheme based on lattices. However, current lattice-based ABE schemes face challenges related to computational complexity and the length of ciphertext and keys. This paper aims to improve the performance of an existing fuzzy IBE scheme by reducing key length and computational complexity during the encryption phase. While negative attributes are not utilized in our scheme, we prove its security under the learning with error (LWE) hard problem assumption in the selective security model. These improvements have significant implications for the field of ABE. [ABSTRACT FROM AUTHOR]

Sharing confidential information is a critical concern in today’s world. Secret sharing schemes facilitate the sharing of secrets in a way that ensures only authorized participants (shareholders) can access the secret using their allocated shares. Hierarchical secret sharing schemes (HSSSs) build upon Shamir’s scheme by organizing participants into different levels based on priority. Within HSSS, participants at each level can reconstruct the secret if a specified number, denoted as the threshold value (t), or more of them are present. Each level has a predetermined threshold value. If the number of participants falls below the threshold at any level, higher-level participants must be involved in reconstructing the secret at lower levels. Our paper proposes schemes that implement hierarchical access structures and enable the sharing of multiple secrets. Additionally, our proposed scheme includes share verification. We have analyzed potential attacks and demonstrated the scheme’s resistance against them. Through security analysis and comparison with existing schemes, we highlight the novelty and superiority of our proposed approach, contributing to advancements in secure information-sharing practices.

Quantum multi-secret sharing plays a vital role in secure multi-key management. In this paper, an authenticable quantum multi-secret sharing scheme based on monotone span program is proposed. In our scheme, the distributor/participants run a quantum state digital signature algorithm to identify dishonest participants, strengthening the proposed scheme's security. During the reconstruction phase, the participants encode their shares onto the generalized Bell states with the generalized Pauli operator to reconstruct multiple secrets. Here, the phase shift operator is utilized to share d-dimensional quantum states. Furthermore, security analysis shows that the proposed scheme can resist the entangle-measure attack, intercept-resend attack, and common internal attacks such as forgery attack, collusion attack, and denial attack. [ABSTRACT FROM AUTHOR]

The Internet of Things (IoT) is a new technology that has drawn interest from both industry and academia in the modern digital era. The IoT provides a platform for any device to connect and share data over the Internet. Because of the diverse IoT environment and resource-constrained IoT devices, this nascent technology has numerous security challenges. Due to the lack of fine-grained access control and flexibility, traditional cryptographic algorithms such as private key encryption and public-key encryption are not suitable for providing access control mechanisms. ABE (Attribute-Based Encryption) is a new cryptographic approach that not only provides security but also fine-grained access control. This paper provides a comprehensive survey of ABE and its various forms, such as key policy ABE and ciphertext policy ABE, based on access structure, multi-authority, and hierarchy features. Further access structures used in ABE and applications of the ABE technique in IoT are also discussed. A comparison of different ABE schemes is presented regarding features, efficiency, and security. In addition, numerous schemes are analyzed to uncover obstacles, issues, and gaps that need to be investigated further. [ABSTRACT FROM AUTHOR]

In cloud storage, data owners usually achieve confidentiality of information through giving encrypted data to the server and as a consequence, the possibility of searching over the database is lost. Searchable encryption (SE) is a method to encrypt data in such a way that keyword searching would still be possible. However, to the best of our knowledge, existing literature on SE schemes only supports search operations carried out by an individual users. In this paper, we introduce the concept of public key encryption with distributed keyword search (PEDKS) to provide a solution for scenarios where the search ability can be distributed among authorized subsets of users according to a predefined access structure. Therefore, by employing a PEDKS, group members realizing the specified access structure can cooperatively query to search. We further propose a concrete construction of a PEDKS scheme and prove its security under the intractability of ECDL and BDH problems. Performance analysis and comparison with related concepts are provided as well. [ABSTRACT FROM AUTHOR]

In this paper, we construct a physical process to mask the d-dimensional quantum state into multipartite quantum systems. According to this masker, we propose a quantum secret sharing scheme to realize a class of special hypergraph access structures. In the distribution phase of the proposed protocol, the distributor wants to share an unknown d-dimensional quantum state and mask the secret state into a multi-party quantum systems. In the reconstruction phase, participants in the authorized set carry out several measurements and a series of appropriate unitary operations on their particles to obtain the original information state. At last, we also analyze the security of our scheme in three primary quantum attacks. [ABSTRACT FROM AUTHOR]

Proxy re-encryption is an essential prerequisite that facilitates a foreign entity (e.g., cloud server) to enforce the access of provisions of a document extended by one user to another user. While performing this task it is essential that the foreign entity does not learn any information about the actual document inside the encrypted envelop. In this paper, we present a scheme on Privacy-preserving Proxy Re-encryption for Access Control in Public Cloud, termed as PAC, that provides the proxy re-encryption of attribute-based encrypted data with receiver privacy. The proposed PAC scheme enables a proxy server to perform the re-encryption operation without learning anything about the data or the access policy. The PAC provides data confidentiality, and preserves receiver privacy. We show the PAC scheme adaptively secure against indistinguishability of ciphertext policy and chosen-plaintext attack (IND-CP-CPA) under the 2-Decisional Bilinear Diffie-Hellman Inversion assumption. The scheme is implemented on Google cloud instance and the experimental results show that the PAC scheme is storage and computation-efficient when compared to other related schemes. [ABSTRACT FROM AUTHOR]

Copyright of Lexikos is the property of Bureau of the Woordeboek van die Afrikaanse Taal and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Authentication is an important primitive of cryptography. With the rapid progress of network communication, the urgent data needs to ensure it integrity and privacy, therefore, the authentication of multi-receiver has a significant impact on the development of network interaction. R. Safavi-Nalni and H. Wang showed that authentication scheme based on Reed-Solomon code is unconditionally secure and allows multiple messages to be authenticated, but the number of receiver to verify is less than q, where the messages are in Fq. In 2014, the secure multi-receiver authentication scheme base on linear code was proposed, however, this scheme can not realize any a given access structure. In this paper, we present a multireceiver authentication scheme to realize any a given ideal access structure, and demonstrate that our scheme is unconditionally secure and allows r messages to be authenticated with each receiver own private key.

Internet of Things (IoT) is a modern technology that is applicable almost everywhere nowadays. Everything is connected to the Internet in the modern digital era. IoT is a collection of things that are interconnected to share information. Devices connected to IoT networks have some limitations in performing heavy computational tasks because of the availability of less computational and battery power. Attribute Based Encryption (ABE) is a modern public-key cryptographic technique that provides privacy with access control. The bilinear map is an expensive operation that is used in most of the ABE schemes. Elliptic Curve Cryptography (ECC) is an alternative for bilinear pairing to reduce the computation of encryption and decryption in ABE schemes. The process of encryption and decryption of ABE is a heavy computational task for resource-constrained devices. In this paper, an outsourcing-based decryption of ABE using ECC is proposed to reduce the decryption overhead of devices that have limited computational resources. Our scheme divides the computation of the decryption of ABE into two stages: first, the partial decryption of ciphertext in the cloud server, and second, the final decryption of partially decrypted ciphertext by the data user to retrieve the original message. This scheme is secure against the malicious cloud server by adding a blinding factor into the secret to be shared. The blinding factor is shared with intended users through attribute authority. The experimental results demonstrate that our scheme can reduce the decryption complexity and save the computational time of devices, compared to the existing schemes. Thus the proposed scheme is applicable for lightweight devices used in IoT. [ABSTRACT FROM AUTHOR]

A group-characterizable (GC) random variable is induced by a finite group, called main group, and a collection of its subgroups. The notion extends directly to secret sharing schemes (SSSs). It is known that linear and abelian SSSs can be equivalently described in terms of GC SSSs. In this paper, we present a necessary and sufficient condition for a SSS to be equivalent to a GC one. Using this result, we show that homomorphic SSSs (HSSSs) are equivalent to GC SSSs whose subgroups are normal in the main group. We also present two applications for this equivalent description of HSSSs. One concerns lower bounding the information ratio of access structures for the class of HSSSs, and the other is about the coincidence between statistical, almost-perfect and perfect security notions for the same class. [ABSTRACT FROM AUTHOR]

Quantum secret sharing plays an important role in quantum cryptography. In this paper, we propose a new general quantum secret sharing scheme based on access structure and monotone span program. In our scheme, the secret distributor first distributes the secret share according to the access structure, and then each participant in the authorization set hides their secret share in the qubits, and then transmits each qubit safely performed on unitary transformation. Compared with the existing quantum secret sharing schemes, our scheme is more flexible, general and less computational cost in practical applications. [ABSTRACT FROM AUTHOR]

XOR-based Visual Cryptography System (XVCS) is developed to achieve high contrast and good resolution of the recovered secret image. In general (k,n) VCS, the secret image can be visualized only if k or more than k shares are stacked together. In (k,n,t)∗ access structure, t number of participants are considered as the essential participants(t ≤ k ≤ n) whose shares are absolutely necessary to reconstruct the secret image. Several methods have been already proposed for the construction of (k,n)∗ VCS for black and white images. The major focus of this work is to design an XVCS for (k,n,t)∗ access structure for both black and white images and color images with maximum contrast. The experimental outcome shows that the proposed method has better results than other techniques proposed so far. Also, numerical examples are provided for (k,n,t)∗ XVCS for t = 1 and 2. The XVCS designed for (k,n,t)∗ access structure can be used for any real time application and is demonstrated with an example of user authentication in banking system. [ABSTRACT FROM AUTHOR]

Cipher text-policy attribute-based encryption schema(CP-ABE) is widely used in protection of sensitive data.In CP-ABE,When the users access the cipher text,the access structure and the cipher text were sent to the users.However,the access structure is also has private information which can lead to leak of the privacy.The group signatures were used in CP-ABE to realize protection of the privacy.What’s more,it can satisfy indistinguishable under the choice of plaintext attack.

Cipher text-policy attribute-based encryption schema(CP-ABE) is widely used in protection of sensitive data. In CP-ABE, When the users access the cipher text, the access structure and the cipher text were sent to the users. However, the access structure is also has private information which can lead to leak of the privacy. The group signatures were used in CP-ABE to realize protection of the privacy.What’s more, it can satisfy indistinguishable under the choice of plaintext attack.

The purpose of this paper is to develop an algorithm for sharing k secret images to n participants in such a way that each participant gets a single share image by encoding all k images. Any qualified subgroup of t : t ≤ n of those n participants can reconstruct the kith secret image only by combining their share images if they are qualified to reconstruct the kith secret image. Most of the existing literature solves this problem for the cases where t = 2 or t = n making it a very restrictive scheme. In this article, we aim to design a multi-secret image sharing scheme based on XOR operation where t is not restricted to be 2 or n. We have used n random matrices of the same size as the secret image size as private share to generate r (where r is the number of qualified subgroups) share images as public share using XOR operations. The proposed scheme is computationally lightweight and lossless due to XOR operation only. It does not involve any pixel expansion. The experimental results with a very low correlation coefficient between share and secret images confirm that share image does not reveal anything about secret image. The scheme is secure against differential attack as a higher value of Number of Changing Pixel rate (NPCR) confirms that. The current proposal is based on a general access structure, and hence any secret image can be reconstructed by a qualified group of t or more shares where t need not be 2 or n only. [ABSTRACT FROM AUTHOR]

The increasing deployment of Internet of Things in diversified fields provides groundwork for smart living. However, at the same time, it brings challenges like security and privacy. Among the numerous proposed security schemes, attribute-based encryption (ABE) is considered as one of the most promising security and privacy preserving scheme in distributed environment (or cloud environment). Many variants of the ABE exist, but most of them employ the expensive bilinear pairing operations. In this article, we have proposed a lightweight elliptic-curve-cryptography-based key-policy ABE without bilinear pairing and having a feature of key refresh/update mechanism. Also, the key distribution is done by the authority, which incorporates direct attribute/user revocation. The scheme is secured under elliptic curve decisional Diffie–Hellman assumption. The performance analysis demonstrates that the proposed scheme is efficient as compared to the existing ABE schemes. [ABSTRACT FROM AUTHOR]

Ciphertext-policy attribute-based encryption (CP-ABE) is a promising cryptographic solution to the problem for enforcing fine-grained access control over encrypted data in the cloud. However, when applying CP-ABE to data outsourcing scenarios, we have to address the challenging issue of policy updates because access control elements, such as users, attributes, and access rules may change frequently. In this paper, we propose a notion of access policy updatable ciphertext-policy attribute-based encryption (APU-CP-ABE) by combining the idea of ciphertext-policy attribute-based key encapsulation and symmetric proxy re-encryption. When an access policy update occurs, data owner is no longer required to download any data for re-encryption from the cloud, all he needs to do is generate a re-encryption key and produce a new encapsulated symmetric key, and then upload them to the cloud. The cloud server executes re-encryption without decryption. Because the re-encrypted ciphertext is encrypted under a completely new key, users cannot decrypt data even if they keep the old symmetric keys or parts of the previous ciphertext. We present an APU-CP-ABE construction based on Syalim et al.’s [Syalim, Nishide and Sakurai (2017)] improved symmetric proxy re-encryption scheme and Agrawal et al.’s [Agrawal and Chase (2017)] attribute-based message encryption scheme. It requires only 6 bilinear pairing operations for decryption, regardless of the number of attributes involved. This makes our construction particularly attractive when decryption is time-critical. [ABSTRACT FROM AUTHOR]

With the development of cloud computing, more and more video services are moving to the cloud. How to realize fine-grained access control of those data on cloud becomes an urgent problem. Attribute-based encryption provides a solution. However, heavy computation is still a bottleneck restricting the wider application of attribute-based encryption in cloud computing. In addition, we find that expression of the access control structure on media cloud can be further improved. To solve these problems, we propose an enhanced media ciphertext-policy attribute-based encryption algorithm and introduce its two key components, the multiple access tree and the key chain. To increase the scalability of the proposed algorithm, we discussed the issues of multi-authorization, user revocation, and 1 − n multiple access tree. Security analysis shows that enhanced media ciphertext-policy attribute-based encryption can successfully resist chosen-plaintext attacks under the decisional bilinear Diffie–Hellman assumption. Performance analysis proves both theoretically and practically that the proposed algorithm incurs less computational cost than the traditional ciphertext-policy attribute-based encryption, multi-message ciphertext-policy attribute-based encryption, and scalable ciphertext-policy attribute-based encryption by optimizing the access control structure. Our proposed algorithm has strong practical significance in media cloud. [ABSTRACT FROM AUTHOR]

Cloud users are outsourcing their data day-by-day resulting in huge amount of data storage in Cloud server. Cloud service provider (CSP) themselves may go for modifying the data that leads to data integrity problem. Unauthorized users illegally gain access to the data stored in cloud server. Therefore, providing protection, achieving privacy and access control for user's data are big challenges in the Cloud. Ciphertext-policy attribute-based encryption (CP-ABE) is prominent encryption technique to solve the exigent dilemma of secure data sharing in cloud computing. The shared data files generally have the characteristic of multilevel hierarchy, predominantly in the areas of IT companies, healthcare and military; these areas require a multi-authority access control. However, the hierarchy construction of shared files and multi-authority access control approach are not been investigated in CP-ABE. This paper proposes an efficient multi-authority access control using attribute-based encryption scheme that achieves efficient, fine grained access control. The proposed scheme consists of one algorithm – (Role Hierarchy Algorithm (RHA) and Hierarchy Access Structure (HAS) to protect user's data, achieve privacy, multi-authority access control and fine grained access to a stored data. The RHA algorithm classifies Cloud users into groups based on their assigned attributes. The HAS helps to define an access structure for fine grained and multi-authority access control of Cloud resources. Simulation results prove that the proposed RHA, HAS are efficient (in terms of time consumption and storage consumption for encryption, decryption) compared to existing works. The advantages of proposed scheme become more and more conspicuous when there is more number of files at Cloud storage server. [ABSTRACT FROM AUTHOR]

In this paper, we study an important problem in secret sharing that determines the exact value or bound for the complexity. First, we use the induced subgraph complexity of the graph G with access structure Γ to obtain a lower bound on the complexity of the graph G. Then, applying decomposition techniques, we obtain an upper bound on the complexity of the graph G. We determine the exact values of the complexity for each of the ten graph access structures on seven participants. Also, we improve the value bound of the complexity for the six graph access structures with seven participants.

Ciphertext-policy attribute-based encryption (CP-ABE) is widely used in many cyber physical systems and the Internet of Things for guaranteeing information security. In order to improve the performance and efficiency of CP-ABE, this paper makes a change to the access structure of describing access polices in CP-ABE, and presents a new CP-ABE system based on the ordered binary decision diagram (OBDD). The new system makes full use of both the powerful description ability and the high calculating efficiency of OBDD. First, in the access structure, the new system allows multiple occurrences of the same attribute in a strategy, supports both positive attribute and negative attribute in the description of access polices, and can describe free-form access polices by using Boolean operations. Second, in the key generation stage, the size of secret keys generated by the new system is constant and not affected by the number of attributes; furthermore, time complexity of the key generation algorithm is O(1). Third, in the encryption stage, both the time complexity of the encryption algorithm and the size of generated ciphertext are determined by the number of valid paths contained in the OBDD instead of the number of attributes occurring in access polices. Finally, in the decryption stage, the new system supports fast decryption and the time complexity of the decryption algorithm is only O(1). As a result, compared with existing CP-ABE schemes, the new system has better performance and efficiency. It is proved that the new CP-ABE system can also resist collision attack and chosen-plaintext attack under the decisional bilinear Diffie Hellman assumption.

In proactive secret sharing schemes, the secret shares are periodically renewed without modifying the secret such that an adversary is unable to get any information about the secret shares unless he is able to obtain a certain number of secret shares in a short time interval. In this paper, using monotone span programs (MSP) we devise a new linear multi-secret sharing (LMSS) scheme which is also multi-stage. We also give a new general method to construct proactive and multi-use linear multi-secret sharing schemes based on MSP. An important advantage of our method compared to the others is that it does not need private channels between each pair of participants or an encryption scheme between them. Finally, we prove that our new scheme satisfies the definition of a perfect LMSS scheme. [ABSTRACT FROM AUTHOR]

Beimel, Tassa and Weinreb [SIAM J. Discrete Math. 22 (2008), 360–397] and Farràs and Padró [Lecture Notes in Comput. Sci. 5978, Springer, 2010, 219–236] partially characterised access structures of ideal weighted secret sharing schemes in terms of the operation of composition. They proved that any weighted ideal access structure is a composition of indecomposable ones. Farràs and Padró gave a list of seven classes of access structures – one unipartite, three bipartite and three tripartite – to which all weighted ideal indecomposable access structures may belong. In this paper we determine exactly which access structures from those classes are indecomposable. We also determine which compositions of indecomposable weighted access structures are again weighted and obtain an if-and-only-if characterisation of ideal weighted secret sharing schemes. We use game-theoretic techniques to achieve this.

The efficiency of secret reconstruction, measured by either channel efficiency or communication efficiency, is always a challenging issue in designing secret sharing schemes and has received considerable attention in recent years. In this letter, aiming at this challenge, we introduce an ingenious strategy, called “jumping skill,” and use it to build a new secret reconstruction scheme. Since only fewer shares are needed to recover the secret, the proposed secret reconstruction scheme is optimal in its communication efficiency. Extensive simulations are conducted, and the results indicate that the upper bound of the communication efficiency can be achieved in our proposal. [ABSTRACT FROM AUTHOR]

A ( k,n )-conventional visual cryptography (VC) scheme is designed to share one secret and each participant takes one share. When some common participants are involved in multiple VC schemes for multiple secrets, each needs to take multiple shares. This procedure needs more shares, which is inconvenient. It is desirable that the collaboration between the VC schemes can allow each common participant to keep only one share. Simply merging or gluing together two traditional ( k_{1} , n_{1} )- and ( k2 , n2 )-VC schemes, after making their pixel expansions the same, might be able to facilitate the collaboration and allow each common participant to keep only one share. But there is a security risk that when a subset of k1 participants are from the collection of noncommon participants, some from scheme 1 and some from scheme 2, they can reconstruct secret 1, which is inconsistent with the intention of the original scheme. Similarly, k2 noncommon participants could reconstruct secret 2. This shortcoming is inherited from the brute-force combination of traditional schemes. Therefore, a more sophisticated mechanism is required; this is the main task of this paper. In this paper, we first transform collaborative VC (CVC) schemes into the multiple secrets VC scheme with a general access structure. The construction of the basis matrices in CVC scheme between two VC schemes is formulated into an integer linear programming problem that minimizes the pixel expansion under the corresponding security and contrast constraints. Also the collaboration among more VC schemes is constructed. Finally, the experimental results illustrate the construction procedure of the CVC scheme and demonstrate the effectiveness of the CVC scheme. [ABSTRACT FROM AUTHOR]

A threshold visual cryptography scheme, denoted as ( k, n )-VCS for short, can encrypt a secret image into n share images. The physical stacking of any k share images can reveal the secret content while any less than k share images will leak no information of the secret content. Besides the threshold access structure, general access structure VCSs are studied in the following works. In this paper, we first build a hyper star access structure VCS from a hyper star without center access structure VCS. Then we build a normal form hyper star access structure VCS from a full threshold VCS, and prove that its pixel expansion is optimal. At last, we propose a method of constructing general access structure VCS from its several decomposed normal form hyper star access structure VCSs. [ABSTRACT FROM AUTHOR]

So far, there have been few descriptions on creating structures capable of storing lexi-cographic data, ISO 24613:2008 being one of the latest. Another one is by Spohr (2012), who designs a multifunctional lexical resource which is able to store data of different types of dictionaries in a user-oriented way. Technically, his design is based on the principle of a hierarchical XML/OWL (eXtensible Markup Language/Web Ontology Language) representation model. This article fol-lows another route in describing a model based on entities and relations between them; MySQL (usually referred to as: Structured Query Language) describes a database system of tables contain-ing data and definitions of relations between them. The model was developed in the context of the project "Scientific eLexicography for Africa" and the lexicographic database to be built thereof will be implemented with MySQL. The principles of the ISO model and of Spohr's model are adhered to with one major difference in the implementation strategy: we do not place the lemma in the centre of attention, but the sense description — all other elements, including the lemma, depend on the sense description. This article also describes the contained lexicographic data sets and how they have been collected from different sources. As our aim is to compile several prototypical internet dictionaries (a monolingual Northern Sotho dictionary, a bilingual learners' Xhosa–English diction-ary and a bilingual Zulu–English dictionary), we describe the necessary microstructural elements for each of them and which principles we adhere to when designing different ways of accessing them. We plan to make the model and the (empty) database with all graphical user interfaces that have been developed, freely available by mid-2015.

In multi‐secret sharing (MSS) scheme, a dealer distributes multiple secrets among a set of participants, each of them according to an access structure. In this study, the authors propose a novel linear MSS with computational verifiability that provide many functions for practical applications in comparison with the previous works focusing on MSS schemes in the general scenario. This scheme has the same advantages as previous schemes; moreover, it is verifiable and multi‐use secret sharing. Furthermore, in this scheme the secret reconstruction is according to the dealer's preassigned order. Also, they prove the security of the authors' scheme in the standard model. [ABSTRACT FROM AUTHOR]

Copyright of SCIENCE CHINA Information Sciences is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

An improving quantum secret sharing scheme (IQSS scheme) was introduced by Nascimento et al. (Phys. Rev. A 64, 042311 (2001)), which was analyzed by the improved quantum access structure. In this paper, we propose a new improving quantum secret sharing scheme, and more quantum access structures can be realized by this scheme than the previous one. For example, we prove that any threshold and hypercycle quantum access structures can be realized by the new scheme. [ABSTRACT FROM AUTHOR]

In this paper, we study an important problem in secret sharing that determines the exact value or bound for the complexity. First, we use the induced subgraph complexity of the graph G with access structure Γ to obtain a lower bound on the complexity of the graph G. Then, applying decomposition techniques, we obtain an upper bound on the complexity of the graph G.We determine the exact values of the complexity for each of the ten graph access structures on seven participants. Also, we improve the value bound of the complexity for the six graph access structures with seven participants. [ABSTRACT FROM AUTHOR]

To protect the sensitive data outsourced to cloud server, outsourcing data in an encrypted way has become popular nowadays. However, it is not easy to find the corresponding ciphertext efficiently, especially the large ciphertext stored on cloud server. Besides, some data owners do not want those users who attempt to decrypt to know the sensitive access structure of the ciphertext because of some business or private reasons. In addition, the user attributes revocation and key updating are important issues, which affect application of ciphertext-policy attribute-based encryption (CP-ABE) in cloud storage systems. To overcome the previous problems in cloud storage, we present a searchable CP-ABE with attribute revocation, where access structures are partially hidden so that receivers cannot extract sensitive information from the ciphertext. The security of our scheme can be reduced to the decisional bilinear Diffie-Hellman (DBDH) assumption and decisional linear (DL) assumption. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

A secret sharing scheme (SSS) was introduced by Shamir in 1979 using polynomial interpolation. Later it turned out that it is equivalent to an SSS based on a Reed-Solomon code. SSSs based on linear codes have been studied by many researchers. However there is little research on SSSs based on additive codes. In this paper, we study SSSs based on additive codes over GF(4) and show that they require at least two steps of calculations to reveal the secret. We also define minimal access structures of SSSs from additive codes over GF(4) and describe SSSs using some interesting additive codes over GF(4) which contain generalized 2-designs. [ABSTRACT FROM AUTHOR]