Doubly Spatial Encryption from DBDH

Functional encryption is an emerging paradigm for public-key encryption which enables fine-grained control of access to encrypted data. Doubly-spatial encryption (DSE) captures all functionalities that we know how to realize via pairings-based assumptions, including (H)IBE, IPE, NIPE, CP-ABE and KP-ABE. In this paper, we propose a construction of DSE from the decisional bilinear Diffie-Hellman (DBDH) assumption. This also yields the first non-zero inner product encryption (NIPE) scheme based on DBDH. Quite surprisingly, we know how to realize NIPE and DSE from stronger assumptions in bilinear groups but not from the basic DBDH assumption. Along the way, we present a novel algebraic characterization of *NO* instances for the DSE functionality, which we use crucially in the proof of security

Fully Secure (Doubly-)Spatial Encryption under Simpler Assumptions

Spatial encryption was first proposed by Boneh and Hamburg in 2008. It is one implementation of the generalized identity-based encryption schemes and many systems with a variety of properties can be derived from it. Recently, Hamburg improved the notion by presenting a variant called doubly-spatial encryption. The doubly spatial encryption is more powerful and expressive. More useful cryptography systems can be builded from it, such as attribute-based encryption, etc. However, most presented spatial encryption schemes are proven to be selectively secure. Only a few spatial encryption schemes achieve adaptive security, but not under standard assumptions. And no fully secure doubly-spatial encryption scheme has been presented before. In this paper, we primarily focus on the adaptive security of (doubly-)spatial encryption. A spatial encryption scheme and a doubly-spatial encryption scheme have been proposed. Then we apply the dual system methodology proposed by Waters in the security proof. Both of the schemes can be proven adaptively secure under standard assumptions, the decisional linear (DLIN) assumption and the decisional bilinear Diffie-Hellman (DBDH) assumption, over prime order groups in the standard model. To the best of our knowledge, our second scheme is the first fully secure construction of doubly-spatial encryption

Search Me If You Can: Privacy-preserving Location Query Service

Location-Based Service (LBS) becomes increasingly popular with the dramatic growth of smartphones and social network services (SNS), and its context-rich functionalities attract considerable users. Many LBS providers use users' location information to offer them convenience and useful functions. However, the LBS could greatly breach personal privacy because location itself contains much information. Hence, preserving location privacy while achieving utility from it is still an challenging question now. This paper tackles this non-trivial challenge by designing a suite of novel fine-grained Privacy-preserving Location Query Protocol (PLQP). Our protocol allows different levels of location query on encrypted location information for different users, and it is efficient enough to be applied in mobile platforms.Comment: 9 pages, 1 figure, 2 tables, IEEE INFOCOM 201

Energy-efficient secure outsourcing decryption of attribute based encryption for mobile device in cloud computation

This is a copy of the author 's final draft version of an article published in the "Journal of ambient intelligence and humanized computing". The final publication is available at Springer via http://dx.doi.org/10.1007/s12652-017-0658-2In this paper two new ways for efficient secure outsourcing the decryption of key-policy attribute-based encryption (KP-ABE) with energy efficiency are proposed. Based on an observation about the permutation property of the access structure for the attribute based encryption schemes, we propose a high efficient way for outsourcing the decryption of KP-ABE, which is suitable for being used in mobile devices. But it can only be used for the ABE schemes having tree-like access structure for the self-enclosed system. The second way is motivated from the fact that almost all the previous work on outsourcing the decryption of KP-ABE cares little about the ciphertext length. Almost all the previous schemes for secure outsourcing the decryption of ABE have linear length ciphertext with the attributes or the policy. But transferring so long ciphertexts via wireless network for mobile phone can easily run out of battery power, therefore it can not be adapted to practical application scenarios. Thus another new scheme for outsourcing the decryption of ABE but with constant-size ciphertexts is proposed. Furthermore, our second proposal gives a new efficient way for secure outsourcing the decryptor’s secret key to the cloud, which need only one modular exponentiation while all the previous schemes need many. We evaluate the efficiency of our proposals and the results show that our proposals are practical.Peer ReviewedPostprint (author's final draft

Contributions to Lattice–based Cryptography

Post–quantum cryptography (PQC) is a new and fast–growing part of Cryptography. It focuses on developing cryptographic algorithms and protocols that resist quantum adversaries (i.e., the adversaries who have access to quantum computers). To construct a new PQC primitive, a designer must use a mathematical problem intractable for the quantum adversary. Many intractability assumptions are being used in PQC. There seems to be a consensus in the research community that the most promising are intractable/hard problems in lattices. However, lattice–based cryptography still needs more research to make it more efficient and practical. The thesis contributes toward achieving either the novelty or the practicality of lattice– based cryptographic systems

Chosen-Ciphertext Secure Attribute-Hiding Non-Zero Inner Product Encryptions and Its Applications

Non-zero inner product encryption (NIPE) allows a user to encrypt a message with an attribute vector and a receiver holding a secret-key associated to a predicate vector can recover the message from the ciphertext if the inner product between the attribute and predicate vectors is non-zero. The main focus is to hide messages in most of the existing NIPEs and the associated attribute is trivially included in the ciphertext. In this work, we investigate the design of NIPEs that are capable of hiding attributes along with messages and secure against active adversaries. In particular, we describe a generic ransformation of an attribute-hiding chosen-ciphertext attack (CCA) secure NIPE from an inner product functional encryption (IPFE) and a quasi-adaptive non-interactive zero-knowledge (QANIZK) proof system. This leads us to a set of attribute-hiding NIPEs (AHNIPE) with security based on several assumptions such as plain Decisional Diffie-Hellman (DDH), Learning With Errors (LWE) and Decision Composite Reciprocity (DCR). Furthermore, we build a more efficient and concrete construction of a CCA secure AHNIPE the security of which can be based on DDH and Kernel Matrix Diffie-Hellman (KerMDH) assumptions. As DDH implies the computational KerMDH assumption, the latter construction achieves a CCA secure AHNIPE from minimal assumption to date. We explore a few applications of AHNIPE. More specifically, we show that AHNIPE directly implies an anonymous identity-based revocation (IBR) scheme. Consequently, we get the first CCA secure IBR solely based on plain DDH assumption in the standard model, improving the security of any previous anonymous CCA secure IBR scheme which is proven secure relying on pairing-based assumptions in the random oracle model. Moreover, we add a tracing algorithm to our anonymous IBR scheme to convert it into an efficient anonymous trace and revoked scheme with CCA security

Delegatable Attribute-based Anonymous Credentials from Dynamically Malleable Signatures

In this paper, we introduce the notion of delegatable attribute-based anonymous credentials (DAAC). Such systems offer fine-grained anonymous access control and they give the credential holder the ability to issue more restricted credentials to other users. In our model, credentials are parameterized with attributes that (1) express what the credential holder himself has been certified and (2) define which attributes he may issue to others. Furthermore, we present a practical construction of DAAC. For this construction, we deviate from the usual approach of embedding a certificate chain in the credential. Instead, we introduce a novel approach for which we identify a new primitive we call dynamically malleable signatures (DMS) as the main ingredient. This primitive may be of independent interest. We also give a first instantiation of DMS with efficient protocols

Advances in Functional Encryption

Functional encryption is a novel paradigm for public-key encryption that enables both fine-grained access control and selective computation on encrypted data, as is necessary to protect big, complex data in the cloud. In this thesis, I provide a brief introduction to functional encryption, and an overview of my contributions to the area

Non-Zero Inner Product Encryption Schemes from Various Assumptions: LWE, DDH and DCR

In non-zero inner product encryption (NIPE) schemes, ciphertexts and secret keys are associated with vectors and decryption is possible whenever the inner product of these vectors does not equal zero. So far, much effort on constructing bilinear map-based NIPE schemes have been made and this has lead to many efficient schemes. However, the constructions of NIPE schemes without bilinear maps are much less investigated. The only known other NIPE constructions are based on lattices, however, they are all highly inefficient due to the need of converting inner product operations into circuits or branching programs. To remedy our rather poor understanding regarding NIPE schemes without bilinear maps, we provide two methods for constructing NIPE schemes: a direct construction from lattices and a generic construction from functional encryption schemes for inner products (LinFE). For our first direct construction, it highly departs from the traditional lattice-based constructions and we rely heavily on new tools concerning Gaussian measures over multi-dimensional lattices to prove security. For our second generic construction, using the recent constructions of LinFE schemes as building blocks, we obtain the first NIPE constructions based on the DDH and DCR assumptions. In particular, we obtain the first NIPE schemes without bilinear maps or lattices

Advances in Design by Metallic Materials: Synthesis, Characterization, Simulation and Applications

Very recently, a great deal of attention has been paid by researchers and technologists to trying to eliminate metal materials in the design of products and processes in favor of plastics and composites. After a few years, it is possible to state that metal materials are even more present in our lives and this is especially thanks to their ability to evolve. This Special Issue is focused on the recent evolution of metals and alloys with the scope of presenting the state of the art of solutions where metallic materials have become established, without a doubt, as a successful design solution thanks to their unique properties