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Smart grids bring advantages of reliabilty and high efficiency by real-time communication technologies in contrast to the traditional grids. However, smart grids also raise concerns about privacy and security for the individual fine-grained information collection. In order to guarantee privacy and securtiy in the grids, we propose an efficient and privacy-preserving multidimensional data aggregation scheme without a third trusted party and supporting fast error detection, named EPMDA-FED, in the paper. Firstly, we adopt Chinese Remainder Theorem to pack multidimensional data and encrypt the processed data using the keys generated by the negotiation among users and the control center. Secondly, our scheme is efficient for encryption without high-cost additive homomorphic public key encryption scheme, such as Paillier cryptosystem and supporting batch verification with fast error detection. Our proposed error detection algorithm is quite efficient with sublinear computation complexity. Besides, through security analysis, EPMDA-FED is semantically secure against collusion attack and the consistency of negotiated key, authenticity and data integrity of the users’ reports are guaranteed. Finally, performance evaluation shows EPMDA-FED is more efficient than existing competing approaches in terms of computation and communication overhead.

Signal processing in the encrypted domain is a potential tool to protect sensitive signals against untrusted cloud servers and malicious users in the delegated computing setting, without affecting the accuracy of signal analyzing and processing. Most existing approaches use Paillier's public key additively homomorphic encryption to encrypt each signal in a large bundle; thus, incurring significant computational costs at local, often resource-constrained, devices while guaranteeing only signal input privacy. To address these limitations, in this paper, an efficient privacy-preserving outsourced discrete wavelet transform scheme (PPDWT), comprising PPDWT-1 and PPDWT-2, without leveraging public key (fully) homomorphic encryption is proposed. Specifically, they are respectively proposed to achieve signal input privacy, coefficient privacy and discrete wavelet transform result privacy against the collusion between honest-but-curious cloud and malicious users. Both constructions leverage the offline execution of any one-way trapdoor permutation only once to encrypt batch signals, and permit signal processing in the encrypted domain. We also discuss the expanding factor, the upper bound and various extensions to privacy-preserving discrete cosine/fourier transform in the encrypted domain. Finally, our proposed PPDWT is formally proved secure under the universal composability (UC) model. We then evaluate the proposed approach using case studies to demonstrate its effectiveness and practicability.

Big data analytics has been regarded as a promising technology to yield better insights into future development by government and industry. Data collection and aggregation are necessary pre-steps to enable data analysis. However, data may be dispersed across multiple places and in different formats. Even worse, data can be encrypted under various encryption mechanisms when data owners try to secure the confidentiality of the data. This makes data aggregation extremely challenging, if not impossible, especially when the encryption keys cannot be shared for various reasons. In this paper, we take the first step in addressing this problem. More specifically, we propose a new notion of cross-domain encryption switching service that securely bridges two well-studied encryption mechanisms, namely traditional public key encryption and identity-based encryption. As of independent interest, our notion supports keyword search over encrypted data, i.e., after encryption switching one may search over the (outsourced) data without loss of data and query secrecy. We provide a provably-secure instantiation satisfying the notion, and further present the efficiency analysis to show the scalability. Our proposed scheme may be applicable in multi-domain cloud storage system.

Location-based service (LBS) in vehicular ad hoc networks (VANETs) has significantly benefited information acquisition from geographically-based social networking. Authentication guarantees the unforgeability and the effectiveness of the LBS information. Unfortunately, owing to a large quantity of redundant or useless LBS messages disseminated in VANETs, the heavy authentication overhead of the existing work adopting a periodically released authentication key, filtering with message identifiers or exploiting public key (fully) homomorphic encryption (FHE), is either intolerable by resource-constrained on-board units (OBUs) or inappropriate to the realtime controlling requirement for VANETs. In this paper, an efficient multi-key secure outsourced computation scheme MSOC without exploiting public key FHE is first proposed, in the setting of two non-colluding servers, namely the cloud and the cryptographic service provider (CSP). Then, based on MSOC, an efficient and secure comparison protocol LSCP is devised, without the interaction between the server and the users. Furthermore, a lightweight privacy-preserving authentication protocol LPPA for LBS in VANETs is proposed, by eliminating duplicate and useless encrypted LBS messages before authentication is executed, through a newly devised efficient privacy-preserving information filtering system. Both user’s location privacy and interest privacy are well protected against even the collusion between the roadside units (RSUs) serving as the cloud (or CSP) and malicious users. Especially, the property of ciphertext re-encryption of our proposed MSOC also guarantees the interest pattern privacy whether two users accept the same LBS information. Finally, formal security proof and extensive simulation results verify the effectiveness and practicability of our proposed LPPA.

In this paper, we introduce a new cryptographic primitive, called autonomous path proxy re-encryption (AP-PRE), which is motivated by several application scenarios where the delegator would like to control the whole delegation path in a multi-hop delegation process. Compared with the traditional proxy re-encryption, AP-PRE provides much better fine-grained access control to delegation path. Briefly speaking, in an AP-PRE scheme, the delegator designates a path of his preferred delegatees. The path consists of several delegatees with the privilege from high to low. If the delegatee in the path cannot complete the decryption, the decryption right is automatically delegated to the next one in the path. In this way, the delegator can ensure that the delegation has always been done among those delegatees the delegator trusts. Moreover, an AP-PRE scheme has to obey the following path rules. The delegation, for ciphertexts of a delegator $i$i, can only be carried out on the autonomous path $\mathsf {Pa}_i$Pai designated by the delegator $i$i, in the sense that (1) re-encrypted ciphertexts along the autonomous path $\mathsf {Pa}_i$Pai cannot branch off $\mathsf {Pa}_i$Pai with meaningful decryption, and (2) original ciphertexts generated under $pk_j$pkj for $j \ne i$j≠i (i.e., for a path $\mathsf {Pa}_j$Paj different from $\mathsf {Pa}_i$Pai) cannot be inserted into (i.e., cannot be transformed along) the autonomous path $\mathsf {Pa}_i$Pai with meaningful decryption. We give the formal definition, as well as the formal security model, for this cryptographic primitive. Under this concept, we construct an IND-CPA secure AP-PRE scheme under the decisional bilinear Diffie-Hellman (DBDH) assumption in the random oracle model. Our scheme is with the useful properties of proxy re-encryption, i.e., unidirectionality and multi-hop.

Public key encryption scheme with keyword search (PEKS) is a promising technique supporting search on encrypted data without leaking any information about the keyword. In real applications, it's critical to find an effective revocation method to revoke users in multi-user cryptosystems, when user's secret keys are exposed.In this paper, we propose the first designated server-aided revocable identity-based encryption scheme with keyword search (dSR-IBKS) from lattice. The dSR-IBKS model requires each user to keep just one private key corresponding with his identity and does not need to communicate with the key generation center or the server during key updating. We have proved that our scheme can achieve chosen keyword indistinguishability in the standard model. In particular, our scheme can designate a unique tester to test and return the search results, therefore no other entity can guess the keyword embedded in the ciphertext by generating search queries and doing the test by itself. We provide a formal security proof of our scheme assuming the hardness of the learning with errors (LWE) problem on the standard model.

Attribute-based encryption received widespread attention as soon as it proposes. However, due to its specific characteristics, the attribute-based access control method is not flexible enough in actual operation. In addition, since access authorities are determined according to users' attributes, users sharing the same attributes are difficult to distinguish. Once a malicious user makes illicit gains by their decryption authorities, it is difficult to trace specific users. This paper follows the practical demand to propose a more flexible key-policy attribute-based encryption scheme with black-box traceability. The scheme has a constant number of constant parameters which can be utilized to construct attribute-related parameters flexibly, and the method of traitor tracing in broadcast encryption is introduced to achieve effective malicious user tracing. In addition, the security and feasibility can be proved by the security proofs and performance evaluation in this paper.

© 2014 IEEE. Machine learning, particularly the neural network (NN), is extensively exploited in dizzying applications. In order to reduce the burden of computing for resource-constrained clients, a large number of historical private datasets are required to be outsourced to the semi-trusted or malicious cloud for model training and evaluation. To achieve privacy preservation, most of the existing work either exploited the technique of public key fully homomorphic encryption (FHE) resulting in considerable computational cost and ciphertext expansion, or secure multiparty computation (SMC) requiring multiple rounds of interactions between user and cloud. To address these issues, in this article, a lightweight privacy-preserving model training and evaluation scheme LPTE for discretized NNs (DiNNs) is proposed. First, we put forward an efficient single key fully homomorphic data encapsulation mechanism (SFH-DEM) without exploiting public key FHE. Based on SFH-DEM, a series of atomic calculations over the encrypted domain, including multivariate polynomial, nonlinear activation function, gradient function, and maximum operations are devised as building blocks. Furthermore, a lightweight privacy-preserving model training and evaluation scheme LPTE for DiNNs is proposed, which can also be extended to convolutional NN. Finally, we give the formal security proofs for dataset privacy, model training privacy, and model evaluation privacy under the semi-honest environment and implement the experiment on real dataset MNIST for recognizing handwritten numbers in DiNN to demonstrate the high efficiency and accuracy of our proposed LPTE.

We develop two variants of Cocks’ identity-based encryption. One variant has faster encryption, where the most time-consuming part only requires several modular multiplications. The other variant makes the first variant anonymous under suitable complexity assumptions, while its decryption efficiency is about twice lower than the first one. Both the variants have ciphertext expansion twice more extensive than the original Cocks’ identity-based encryption. To alleviate the issue of the second variant’s large ciphertext expansion, we consider using it to construct a public-key encryption with keyword search scheme with a fast encryption algorithm by means of the transform in [1].

Ciphertext-policy attribute-based encryption, denoted by CP-ABE, extends identity based encryption by taking a set of attributes as users’ public key which enables scalable access control over outsourced data in cloud storage services. However, a decryption key corresponding to an attribute set may be owned by multiple users. Then, malicious users are subjectively willing to share their decryption keys for profits. In addition, the authority who issues decryption keys in CP-ABE system is able to generate arbitrary decryption key for any (including unauthorized) user. Key abuses of both malicious users and the authority have been regarded as one of the major obstacles to deploy CP-ABE system in real-world commercial applications. In this paper, we try to solve these two kinds of key abuses in CP-ABE system, and propose two accountable CP-ABE schemes supporting any LSSS realizable access structures. Two proposed accountable CP-ABE schemes allow any third party (with the help of authorities if necessary) to publicly verify the identity of an exposed decryption key, allow an auditor to publicly audit whether a malicious user or authorities should be responsible for an exposed decryption key, and the key abuser can’t deny it. At last, we prove the two schemes can achieve publicly verifiable traceability and accountability.

The Internet of Things is increasingly becoming a ubiquitous computing service, requiring huge volumes of data storage and processing. Unfortunately, due to the unique characteristics of resource constraints, self-organization, and shortrange communication in IoT, it always resorts to the cloud for outsourced storage and computation, which has brought about a series of new challenging security and privacy threats. In this article, we introduce the architecture and unique security and privacy requirements for the next generation mobile technologies on cloud-based IoT, identify the inappropriateness of most existing work, and address the challenging issues of secure packet forwarding and efficient privacy preserving authentication by proposing new efficient privacy preserving data aggregation without public key homomorphic encryption. Finally, several interesting open problems are suggested with promising ideas to trigger more research efforts in this emerging area.

Cognitive radio network (CRN) enables dynamic spectrum management where spectrum aggregation and sharing have significantly facilitated relieving the supply-demand gap among skyrocketing number of mobile devices. Secondary users (SUs) can collaboratively detect and exploit the available spectrums of primary users (PUs) from different locations. Unfortunately, it has brought a series of security threats leaking user's location privacy to unauthorized entities. The existing work either had privacy breaches or depended on computationally-intensive public key homomorphic encryption loading intolerably high complexity on resource-constrained SUs. To well address these issues, in this paper, a lightweight privacy-preserving spectrum aggregation and auction scheme PPSAS is proposed in CRNs without leveraging public key homomorphic encryption. Firstly, a new primitive of efficient privacy preserving multiparty data aggregation protocol PPMDA is proposed based on any one-way trapdoor permutation. Then based on PPMDA, an efficient privacy preserving spectrum aggregation scheme PPSRA and spectrum auction scheme PPSSA are respectively devised to constitute our proposed PPSAS. Especially, a decentralized PPMDA is extended to resist collusion attack and a secure extended outsourced stable complete marriage matching protocol is given to flexibly realize SU/auctioneer optimization. Finally, formal security proof and extensive simulations demonstrate that our proposed PPSAS well protects the SUs' location privacy against collusion attacks and possesses the advantages over the sate-of-the-art in terms of auctioneer's revenue, SUs' satisfaction, computational and communication overhead.

In this paper, we propose a revocable public key encryption with authorized keyword search (RPEAKS) scheme. In RPEAKS, data and keywords are encrypted with one public key, users without corresponding private key need authorization from the manager if they want to search through the ciphertexts. The manager authorizes users by distributing authorized tokens to them and is able to revoke a user’s search right when needed. Then we present a concrete RPEAKS construction, which is featured with constant size tokens and efficient revocation. Security analysis shows that the scheme is semantically secure against chosen keyword attack and is trapdoor unforgeability.

Security and privacy is a prerequisite for the development of mobile networking in big data era. However, security scheme usually demands complex and inefficient implementation. One interesting difference between mobile social networks (MSNs) and web-based social networks is that: user in MSNs is identified by a bunch of serial numbers, while in traditional web-based social network, is identified by arbitrarily strings. Two obvious examples are the phone number in mobile networks and the license number in vehicular ad hoc networks. Taking advantage of this minor difference, we develop a lightweight functional public key encryption scheme and demonstrate its applications for mobile networks. We call such a scheme the Serial Number Based Encryption (SNBE). Our scheme is provable secure base on the DBDH assumption in the standard model, while the ciphertext consists of only three elements.

With the emerging techniques of wireless communication and cloud computing, large volumes of multimedia data are outsourced from resource-constrained users to the cloud with abundant resource for both delegated storage and computation. Unfortunately, there exists a risk of users’ image privacy leakage in the process of outsourcing to the cloud in the malicious setting. Most of the existing work achieved privacy-preserving verifiable image feature extraction and matching by using public key (fully) homomorphic encryption (FHE), and the heavy computational overhead and communication overhead cannot adapt to resource-constrained mobile devices. Other works disabled to achieve image denoising in the encrypted domain or only focused on the scale-invariant feature transform (SIFT) descriptor that is inappropriate for position-sensitive feature extraction. To address these issues, in this paper, a privacy-preserving verifiable shape context based image denoising and matching protocol PVIDM with efficient outsourcing in the malicious setting is proposed. To achieve this end, by exploiting any one-way trapdoor permutation, an efficient privacy-preserving verifiable image denoising scheme PPVID is firstly proposed to improve the accuracy of image matching, without exploiting public key FHE. Then, based on PPVID, a lightweight shape context based privacy-preserving verifiable image feature extraction and matching protocol PPVIM is devised, where secure and efficient comparison and counting protocols in the encrypted domain are respectively proposed. Both image privacy and image matching result privacy are well protected, and the correctness of image matching result can be efficiently verified. Finally, formal security proof and extensive simulations on real-world data sets demonstrate the efficiency and practicability of our proposed PVIDM. Especially, both the computational complexity for the usage of any one-way trapdoor permutation at data owner’s/user’s end and the size of the authentication tag generated by the cloud are O(1), independent to both the number of database images and the number of pixels in each image.

Cloud computing has an significant impact on both academia and industry with its rapid development. by moving expensive operations like search to cloud, we are able to carry out complicated tasks efficiently. At the same time, cloud security has become a major concern. Malicious clouds are likely to sell privacy information for extra benefit. In order to protect privacy, data are encrypted before being uploaded to cloud. So how to handle encrypted data becomes a new challenge. In this paper we propose SDKSE: a secure dynamic keyword searchable encryption scheme for email systems under cloud computing environment. It is able to update files and keywords at any time. The indexes and the trapdoors generated in the scheme are constant size. In addition, we prove that it is adaptively Trapdoor-IND-CKA and Index-IND-CKA in the standard model.

With the emerging techniques of wireless communication and cloud computing, large volumes of multimedia data are outsourced from resource constrained users to the cloud with abundant resource for both delegated storage and computation. Unfortunately, there is a risk of users’ image privacy leakage in the process of outsourcing to untrusted cloud. Most of the existing work achieved privacy-preserving image feature extraction and matching by using public key (fully) homomorphic encryption (FHE), but the heavy computational overhead and communication overhead cannot adapt to resource-constrained mobile devices. Other works disabled to realize image denoising in the encrypted domain or only focused on the scale-invariant feature transform (SIFT) descriptor that is inappropriate for position-sensitive feature extraction. To address these issues, in this paper, a privacy-preserving shape context based image denoising and matching protocol PPOIM with efficient outsourcing is proposed. Firstly, to improve the accuracy of image matching, a privacy-preserving image denoising scheme PPID is proposed without exploiting public key FHE. Then, based on PPID, a privacy-preserving image matching protocol PPOIM adopting shape context descriptor is devised, where two secure and efficient comparison and counting protocols in the encrypted domain are presented. All the original image privacy, query image privacy and image matching result privacy are well protected. Finally, formal security proof and extensive simulations on real-world data sets demonstrate the efficiency and practicability of our proposed PPOIM.

Searchable encryption has emerged in order to maintain the balance between data privacy and convenience of keyword search. In 2017, Huang et al. introduced the notion of inside keyword guessing attack (IKGA), which means the inside adversary could try out the keyword specified by a given trapdoor by guessing offline and proposed a scheme called Public-key Authenticated Encryption with Keyword Search (HQ-PAEKS) to solve this problem. However, the search complexity of HQ-PAEKS is linear to the total number of the encrypted indexes and may be not in a position to meet the demand of practical application. This paper combines the idea of Public-key Authenticated Encryption with hidden structure and proposes a practical scheme called Public-key Authenticated Encryption with Fast Keyword Search (PAEFKS), in which the search complexity for the cloud server presents linear relation with the number of the encrypted indexes matching the trapdoor sent from the data user. In addition, it gives security analysis to show that the scheme could protect index and keyword privacy well and experiments on real-world data sets show that the scheme indeed reduces the overhead on keyword search computation in the cloud.

This paper continued the research line of dual system groups (DSG) opened by Chen and Wee (CRYPTO, 2013 and IACR Cryptology ePrint Archive, 2014). Motivated by Lewko's unbounded hierarchical identity based encryptions (HIBE) (EUROCRYPT, 2012), we extended Chen and Wee's DSG and showed how to construct an unbounded HIBE from our extended DSG. Furthermore, an instantiation of our extended DSG was given using prime-order bilinear groups under the d-Lin assumption. These two results imply an adaptively secure unbounded HIBE in the standard model with not only shorter ciphertexts and user's secret keys but also faster algorithms than Lewko's construction.

Distributed m-healthcare cloud computing system significantly facilitates efficient patient treatment for medical consultation by sharing personal health information among healthcare providers. However, it brings about the challenge of keeping both the data confidentiality and patients’ identity privacy simultaneously. Many existing access control and anonymous authentication schemes cannot be straightforwardly exploited. To solve the problem, in this paper, a novel authorized accessible privacy model (AAPM) is established. Patients can authorize physicians by setting an access tree supporting flexible threshold predicates. Then, based on it, by devising a new technique of attribute-based designated verifier signature, a patient self-controllable multi-level privacy-preserving cooperative authentication scheme (PSMPA) realizing three levels of security and privacy requirement in distributed m-healthcare cloud computing system is proposed. The directly authorized physicians, the indirectly authorized physicians and the unauthorized persons in medical consultation can respectively decipher the personal health information and/or verify patients’ identities by satisfying the access tree with their own attribute sets. Finally, the formal security proof and simulation results illustrate our scheme can resist various kinds of attacks and far outperforms the previous ones in terms of computational, communication and storage overhead.

Ciphertext-policy attribute-based encryption (CP-ABE) is a promising public key encryption primitive enabling fine-grained access control on shared data in public cloud. However, two quite challenging issues, the prevention of key escrow and key abuse, still exist in CP-ABE system. In this paper, we propose a multi-authority CP-ABE scheme without key escrow and key abuse. To prevent key escrow, multiple authorities are employed to perform the same procedure of key generation for an attribute. Thus, no individual authority or colluded authorities that manage no common attribute can decrypt any ciphertext, and it can also resist collusion attack from curious authority with the help of dishonest users. To prevent key abuse of dishonest users, user’s global identifier along with a signature is embedded into the secret key. Thus, any third party can learn the identity from a shared secret key and publicly verify its validity. An advantage of simultaneously preventing key escrow and key abuse is that the proposed scheme can achieve accountability, i.e. an auditor can publicly audit a user or authorities abuse the secret key. At last, the proposed scheme is fully secure in the random oracle model, and due to a key aggregate algorithm its efficiency is comparable to the decentralizing CP-ABE scheme [18] on which it is based.

Outsourced pattern matching delegates the task of finding all positions pattern $P$ P appears in text $T$ T to the cloud from resource-constrained devices. Unfortunately, it has brought a series of security and privacy issues. Most of the state-of-the-art either disclosed text/pattern privacy or exploited the computationally-intensive techniques of public key fully homomorphic encryption (FHE), commitment schemes and zero knowledge proof to achieve both text/pattern privacy and verifiability. To address these issues, as a building block, an efficient privacy preserving verifiable outsourced discrete fourier transform protocol OVFT is first devised based on any one-way trapdoor permutation (OWTP). Based on OVFT, we propose an efficient secure verifiable outsourced polynomial multiplication protocol OPVML which is further exploited in designing our final protocol PVOPM for verifiable privacy-preserving outsourced pattern matching. Without exploiting public key FHE, the proposed PVOPM achieves both verifiability and text/pattern privacy against the collusion between the cloud and malicious receiver/sender, by generating authentication proofs of constant size and executing constant times of any one-way trapdoor permutation, independent to both the text size $n$ n and the pattern size $m$ m . Finally, formal security proof under universal composable (UC) model and extensive evaluations demonstrate the efficiency and practicability of our proposed PVOPM.

We present the concept of a certificate-based proxy decryption (CBPd) system with revocability, which has the following properties: (1) key-escrow freeness; (2) implicit certification; (3) revocability without public key change; and (4) fine-grained delegation. A concrete CBPd scheme is also proposed. The scheme is semantically secure against adaptive chosen plaintext attack (IND-CBPd-Rev-CPA) under the decisional bilinear Diffie-Hellman assumption in the standard model. We also give an enhanced scheme that is secure against adaptive chosen ciphertext attacks (IND-CBPd-Rev-CCA) in the standard model.

In distributed collaborative networks such as peer-to-peer systems, privacy preserving information sharing and dissemination heavily relies on effective trust management. Trust based encryption (TBE) has been proposed to be a solution to enabling privacy preserving information sharing and dissemination for such networks. Unfortunately, the previously proposed schemes are not efficient in terms of communications overhead, and require a constantly online trust authority. In this paper, we propose two trust based encryption schemes with significantly improved efficiency. In the first scheme, we develop a generic transformation approach based on the recently proposed identity based broadcast encryption (IBBE) technique, which can significantly reduce both memory space and communication overhead when static reputation is considered. For the dynamic reputation scenarios, we present a trust based encryption scheme which is based on a recently proposed revocable identity based encryption technique, resulting in significantly reduced communication overhead at the central trust authority.

In this paper, we present a new identity-based encryption IBE scheme using bilinear pairings. Compared with the famous IBE scheme of Boneh and Franklin, ours is more practical in the multiple private key generator multiple-PKG environment. We prove that our scheme meets chosen ciphertext security in the random oracle model, assuming the intractability of the standard bilinear Diffie-Hellman problem. Copyright © 2013 John Wiley & Sons, Ltd.

Two novel public key encryption schemes based on the non-Abelian factorization problems were proposed. Both of them are proved to be indistinguishable against adaptively chosen ciphertext attack (IND-CCA2) in the random oracle models. These constructions have the potential to resist Shor's quantum algorithm attack proposed in 1994 and give affirmative answers for the open question announced by Myasnikov, Shpilrain and Ushakov in 2011. Copyright © 2013 John Wiley & Sons, Ltd.

In 2009, Wu proposed a fast modular exponentiation algorithm and claimed that the proposed algorithm on average saved about 38.9% and 26.68% of single-precision multiplications as compared to Dusse-Kaliski's Montgomery algorithm and Ha-Moon's Montgomery algorithm, respectively. However, in this comment, we demonstrate that Wu's algorithm on average reduces the number of single-precision multiplications by at most 22.43% and 6.91%, when respectively compared with Dusse-Kaliski's version and Ha-Moon's version. That is, the computational efficiency of Wu's algorithm is obviously overestimated.

Secure outsourced pattern matching permits both the sender and receiver with resource-constrained mobile devices to respectively delegate text T and pattern P to the cloud for the computationally-intensive task of pattern matching. Unfortunately, outsourcing both the computation and storage to the semi-trusted or malicious cloud has brought a series of security and privacy issues. Most of the state-of-the-art exploited the technique of computationally-intensive public key (fully) homomorphic encryption (FHE) as primitives which is inappropriate for resource-constrained devices and the work not depending on FHE cannot well guarantee either text privacy or pattern privacy. To well address this problem, a more efficient privacy preserving outsourced pattern matching PPOPM is proposed in this paper. As a building block, a privacy preserving outsourced discrete fourier transform protocol OFFT is firstly devised to allow the cloud perform OFFT in the encrypted domain, without disclosing either the coefficient privacy or the input privacy. Based on OFFT, we propose an efficient secure outsourced polynomial multiplication protocol OPMUL which is further exploited in designing the final efficient outsourced pattern matching protocol PPOPM. Without exploiting public key FHE, the proposed PPOPM achieves secure outsourced pattern matching with well protected text privacy and pattern privacy against the collusion between the cloud and the receiver or the sender, by performing any one-way trapdoor permutation only once. Finally, the universal composable (UC) technique is adopted to formally prove the security of our proposed PPOPM under the semi-honest environment. The extensive evaluations demonstrate the efficiency and practicability of our proposed PPOPM.

Ciphertext-policy attribute-based encryption (CP-ABE) is a highly promising solution for cloud computing, which has been widely applied to provide fine-grained access control in cloud storage services recently. However, for CP-ABE based cloud storage systems, if a decryption device appears on eBay described and advertised to be able to decrypt any ciphertexts with policies satisfied by an attribute set or even with a specific access policy only, no one can trace the malicious user(s) who built such a decryption device using their private key(s). This has been known as a major obstacle to deploying CP-ABE systems in real-world commercial applications. Due to the one-to-many encryption mechanism of CP-ABE, the same decryption privilege is shared by multiple users who have the same attributes. It is difficult to identity the malicious user(s) who built such a decryption device. To track people selling decryption devices on eBay efficiently, in this paper, we develop a new methodology for constructing traitor tracing functionality, and present the first black-box traceable CP-ABE (BT-CP-ABE) with short ciphertexts which are independent of the number of users \(\mathcal {N}\). The black-box traceability is public, fully collusion-resistant, and adaptively traceable against both key-like decryption black-box and policy-specific decryption black-box.

Ciphertext-policy attribute-based encryption, denoted by CP-ABE, is a promising extension of identity-based encryption which enables fine-grained data access control by taking a set of attributes as users' public key. However, owing to the fact that an attribute set may be shared by multiple users, malicious users dare to share their decryption keys to others for profits. Furthermore, the central authority is able to issue arbitrary decryption keys for any unauthorized users. To prevent these two kinds of key abuses in CP-ABE system, we propose an accountable CP-ABE scheme which allows any third party to publicly verify the identity embedded in a leaked decryption key, allows an auditor to publicly check whether a malicious user or the authority should be responsible for an exposed decryption key, and the malicious user or the authority can't deny it. The proposed accountable CP-ABE scheme supports any LSSS realizable access structures. At last, the confidentiality and public verifiability of the proposed scheme can be proved to be tightly related to the atomic CP-ABE scheme and the signature scheme that it composed from.

We introduce a new cryptographic primitive which is the signature analog of fuzzy identity based encryption (FIBE). We call it fuzzy identity based signature (FIBS). It possesses similar error-tolerance property as FIBE that allows a user with the private key for identity @w to decrypt a ciphertext encrypted for identity @w' if and only if @w and @w' are within a certain distance judged by some metric. We give the definition and security model of FIBS and present the first practical FIBS scheme. We prove that our scheme is existentially unforgeable against adaptively chosen message attack in the standard model. To our best knowledge, this primitive was never considered in the identity based signature before. FIBS is of particular value for biometric authentication, where biometric identifiers such as fingerprints, iris, voice and gait are used in human identification. We demonstrate the applicability of our construction to secure biometric authentication.

Service-oriented vehicular ad hoc networks (VANETs) are expected to support the diverse infrastructure-based commercial services, including Internet access, real-time traffic concerns, video streaming, and content distribution. The success of service-oriented VANETs depends on the underlying communication system to enable the user devices to connect to a large number of communicating peers and even to the Internet. This poses many new research challenges, particularly on the aspects of security and user's privacy. In this paper, we propose a novel privacy-preserving data-forwarding scheme based on our proposed novel Lite-CA-based public key cryptography and on-path onion encryption technique. The proposed scheme is expected to not only thwart the traffic tracing attack at the minimized computational overhead but to provide an efficient way to relieve workload and deployment complexity of certificates as well. Performance comparisons and security analysis show that the proposed schemes are very efficient and suitable for service-oriented VANETs.

With the rapid development of cloud computing, more and more users store their data in the cloud. Considering the privacy problem of the data sharing in the cloud, searchable encryption makes it possible to efficiently share and retrieve data in multi-user settings. The existing keyword search scheme of sharing the private key with authorized users to generate trapdoors may increase the risk of key exposure, and the scheme of encrypting the data with the secret key of each authorized user and generating a ciphertext for each user may not be suitable for data sharing between a large number of users. In this paper, we combine the secure IBBE system with the keywords search and propose the scheme to achieve safe and efficient multi-user data sharing in the cloud. Authorized users can perform keyword search directly on encrypted data without sharing the secret key, and for a shared file, the data owner only needs to encrypt one ciphertext for all authorized users. Besides, authorized users of shared files can be revoked. User authorization tables and IBBE ensure that revoked users cannot access files.

This paper investigates the security model for authenticated key exchange protocols. We further enhance the enhanced Canetti-Krawczyk (eCK) model by introducing a notion called strong key compromise impersonation (SKCI) resilience which is first identified in this paper. SKCI resilience guarantees that the adversary cannot masquerade as another party B to communicate with party A even if the static private key and the ephemeral private key of party A are compromised. We point out that the three-pass authenticated key exchange protocol generically transformed from the two-pass one secure in the eCK model cannot resist the SKCI attack. Finally, we introduce a new authenticated key exchange protocol SIG-DH+ and prove that it satisfies our new definition. Copyright © 2010 John Wiley & Sons, Ltd.

We introduce a new cryptographic primitive, called proxy re-encryption with keyword search, which is motivated by the following scenario in email systems: Charlie sends an encrypted email, which contains some keywords, such as ''urgent'', to Alice under Alice's public key, and Alice delegates her decryption rights to Bob via her mail server. The desired situations are: (1) Bob can decrypt mails delegated from Alice by using only his private key, (2) Bob's mail gateway, with a trapdoor from Bob, can test whether the email delegated from Alice contains some keywords, such as ''urgent'', (3) Alice and Bob do not wish to give the mail server or mail gateway the access to the content of emails. The function of proxy re-encryption with keyword search (PRES) is the combination of proxy re-encryption (PRE) and public key encryption with keyword search (PEKS). However, a PRES scheme cannot be obtained by directly combining those two schemes, since the resulting scheme is no longer proven secure in our security model. In this paper, a concrete construction is proposed, which is proven secure in the random oracle model, based on the modified Decisional Bilinear Diffie-Hellman assumption.

The development of quantum computation casts serious threats to the securities of most existing public-key cryptosystems. Braid-based cryptography is one of the alternatives that have potential advantages in resisting quantum attacks. In this paper, the state of the art of braid cryptography is surveyed, and then a new cryptographic problem—conjugate adjoining problem related to braid groups is proposed. Based on this problem, we design a new braid-based signature scheme. This scheme is efficient and provably secure in the random oracle model. Further, we present the comparison between braid-based signatures and RSA-based ones. The signing process of the braid-based schemes is more efficient than that of RSA-based ones, while the verifying process of the braid-based ones is observably slow. Hence, braid-based signatures are suitable for scenarios where the signing process has to be as quick as possible but delays are permitted in the verifying process, for example, in off-line e-cash systems. The key sizes in braid-based schemes are considerably large—about 2K bits in the case of secret keys and 12K bits in the case of public keys. However, braid operations are much simpler and more efficient than modular exponential operations. Therefore, braid-based schemes can be embedded into devices with low computational ability and large memory space. The capability of braid cryptosystems to resist currently known quantum attacks is also discussed from the perspective of hidden subgroup problems.

Threshold decryption allows a message encrypted under a public key to be read only when a quorum of users cooperate to decrypt the ciphertext. However, such threshold decryption scheme does not apply well in the situation where all the users have their own public/private key pairs, but not share any private key associated with a public key, such as mobile ad hoc network featured by its dynamic character. An immediate way to achieve threshold decryption in this situation is to split the message into pieces, then encrypt these pieces under the public keys of different users. However, it is not efficient. In this paper, we propose an efficient identity based multi-receiver threshold decryption scheme that could be applied efficiently in the above situation. We also define the security notions and prove the security in random oracle model. At last, we add the broadcast feature to the scheme, such that a message could be broadcast to any number of groups.

We analyze the relationship between the notion of certificateless public key cryptography (CL-PKC) and identity-based schemes without a trusted private key generator (PKG), formally define the security of certificateless threshold signatures, and propose a concrete implementation based on bilinear pairings. To exhibit the security of our proposal, we develop the theory of simulatability and relationship between the certificateless threshold signatures and the underlying (non-threshold) ID-based signatures. We show that the proposed scheme is robust and existentially unforgeable against adaptively chosen message attacks under CDH assumption in the random oracle model.

Three-party authenticated key exchange protocol is an important cryptographic technique in the secure communication areas, by which two clients, each shares a human-memorable password with a trusted server, can agree a secure session key. Over the past years, many three-party authenticated key exchange protocols have been proposed. However, to our best knowledge, not all of them can meet the requirements of security and efficiency simultaneously. Therefore, in this paper, we would like to propose a new simple three-party password based authenticated key exchange protocol. Compared with other existing protocols, our proposed protocol does not require any server's public key, but can resist against various known attacks. Therefore, we believe it is suitable for some practical scenarios.

Multi-decrypter encryption is a typical application in multi-user cryptographic branches. In multi-decrypter encryption, a message is encrypted under multiple decrypters' public keys in the way that only when all the decrypters cooperate, can the message be read. However, trivial implementation of multi-decrypter encryption using standard approaches leads to heavy computation costs and long ciphertext which grows as the receiver group expands. This consumes much precious bandwidth in wireless environment, such as mobile ad hoc network. In this paper, we propose an efficient identity based multi-decrypter encryption scheme, which needs only one or zero (if precomputed) pairing computation and the ciphertext contains only three group elements no matter how many the receivers are. Moreover, we give a formal security definition for the scheme, and prove the scheme to be chosen ciphertext secure in the random oracle model, and discuss how to modify the scheme to resist chosen ciphertext attack.

A popular methodology of designing cryptosystems with practical efficiency is to give a security proof in the random oracle RO model. The work of Fischlin and Fleischhacker Eurocrypti¾?'13 investigated the case of Schnorr signature and generally, Fiat-Shamir signatures and showed the reliance of RO model is inherent. We generalize their results to a large class of "malleable" hash-and-sign signatures, where one can efficiently "maul"any two valid signatures between two signature instances with different public keys if it can get the difference between the secret keys. We follow the technique of Fischlin and Fleischhacker to show that the security of malleable hash-and-sign signature cannot be reduced to its related hard cryptographic problem without programming the RO. Our proof assumes the hardness of a one-more cryptographic problem depending on the signature instantiation. Our result applies to single-instance black-box reductions, subsuming those reductions used in existing proofs. Our framework not only encompasses Fiat-Shamir signatures as special cases, but also covers $$\Gamma $$-signature Yao and Zhao, IEEE Transactions on Information Forensics and Securityi¾?'13, and other schemes which implicitly used malleable hash-and-sign signatures, including Boneh-Franklin identity-based encryption, and Sakai-Ohgishi-Kasahara non-interactive identity-based key exchange.

Wu and Hsu proposed a (t,n) threshold signature scheme using self-certified public keys in order to integrate the properties of self-certified public key schemes and threshold signature schemes. Even though their scheme is more efficient when compared to previous works based on the certificate-based public key systems, we find some design defects of their scheme. In this paper, by identifying some concrete instances and analyses we will show that their scheme is not as secure as they claimed.

In this paper, we first present a self-certified public key system based on the improved Rabin scheme. Subsequently, a self-certified public key based proxy signature scheme is proposed whose security is not loosely related to discrete logarithm assumption as most of the traditional schemes but tightly related to the decisional Diffie-Hellman (DHH) assumption in the Random Oracle models.

Recently, Peinado proposed a modification on Lee-Hwang-Li's public key authentication scheme. Peinado claimed that the modified scheme achieves non-repudiation of the user's public key. However, we show that a dishonest user can forge his public key via the verification equation. Hence, Peinado's scheme cannot achieve the non-repudiation service, like the previous versions. And then, an improved public key authentication scheme is proposed. Finally, we prove that our improved scheme can provide the non-repudiation service for the user's public key.

To provide non-repudiation of the user's public key, Lee et al. proposed an improved public key authentication scheme for cryptosystems based on discrete logarithms in 2003. However, we demonstrate that a dishonest user can forge the public key via the verification equation. Therefore, this scheme cannot achieve the non-repudiation service like its previous versions.

Recently, Zhang and Kim proposed an improved key authentication scheme [Appl. Math. Comput., in press]. Zhang and Kim claimed that the proposed key authentication scheme achieves the non-repudiation service. However, we show that a dishonest user can forge his public key via the verification equation. Hence this scheme cannot achieve the non-repudiation service like the previous variants.

The concept of proxy signature introduced by Mambo, Usuda, and Okamoto allows a designated person, called a proxy signer, to sign on behalf of an original signer. However, most existing proxy signature schemes do not support nonrepudiation. In this paper, two secure nonrepudiable proxy multi-signature schemes are proposed that overcome disadvantages of the existing schemes. The proposed schemes can withstand public key substitution attack. In addition, the new schemes have some other advantages such as proxy signature key generation and updating using insecure channels. This approach can also be applied to other ElGamal-like proxy signature schemes.

An unlinkable secret handshakes is a two-party authentication protocol which protects the privacy of parties' affiliation and identity to everyone except for the intended parties. However, we find that the latest solution proposed by Jarecki et al. is not very efficient. In particular, each party requires O(log n) exponentiations where n is the number of parties affiliated with a single organization. In this paper, we propose a novel unlinkable secret handshakes protocol. Compared with Jarecki et al's scheme, our proposal is simple intuitionally and requires only constant exponentiations.

In SAC'05, Strangio proposed protocol ECKE- 1 as an efficient elliptic curve Diffie-Hellman two-party key agreement protocol using public key authentication. In this letter, we show that protocol ECKE-1 is vulnerable to key-compromise impersonation attacks. We also present an improved protocol - ECKE-1N, which can withstand such attacks. The new protocol's performance is comparable to the well-known MQV protocol and maintains the same remarkable list of security properties.

In this paper, we propose a two-level path authentication protocol for object genuineness verification in RFID-based supply chain and EPCglobal Network. In our solution, a tag's path in a supply chain can be generated dynamically, where each reader in the path can verify the validation of the path using its own private key. Our solution has a few promising properties, including dynamic path generation, distributed authentication, and scalability. In comparison, the previous path authentication solution for RFID tags is focused on static path generation and centralized control. The efficiency of our path authentication protocol is enhanced significantly by dividing a whole path into multiple segments according to organization structures. The security and privacy of our protocol are established based on two cryptographic primitives, hierarchical identity-based encryption and batch verification signature.