Fine-Grained Secure Computation

This paper initiates a study of Fine Grained Secure Computation: i.e. the construction of secure computation primitives against moderately complex adversaries. We present definitions and constructions for compact Fully Homomorphic Encryption and Verifiable Computation secure against (non-uniform) $\mathsf{NC}^1$ adversaries. Our results do not require the existence of one-way functions and hold under a widely believed separation assumption, namely $\mathsf{NC}^1 \subsetneq \oplus \mathsf{L} / \mathsf{poly}$. We also present two application scenarios for our model: (i)hardware chips that prove their own correctness, and (ii) protocols against rational adversaries potentially relevant to the Verifier\u27s Dilemma in smart-contracts transactions such as Ethereum

Ciphertext Policy Attribute based Homomorphic Encryption (CP-ABHERLWE): a fine-grained access control on outsourced cloud data computation

Recently, homomorphic encryption is becoming one of the holy grail in modern cryptography research and serve as a promising tools to protect outsourced data solutions on cloud service providers. However, most of the existing homomorphic encryption schemes are designed to achieve Fully Homomorphic Encryption that aimed to support arbitrary computations for only single-data ownership scenario. To bridge these gaps, this paper proposed a non-circuit based Ciphertext Policy-Attribute Based Homomorphic Encryption (CP-ABHER-LWE) scheme to support outsourced cloud data computations with a fine-grained access control under the multi-user scenario. First, this paper incorporates Attribute Based Encryption (ABE) scheme into homomorphic encryption scheme in order to provide a fine grained access control on encrypted data computation and storage. Then, the proposed CP-ABHER-LWE scheme is further extended into non-circuit based approach in order to increase the practical efficiency between enterprise and cloud service providers. The result shows that the non-circuit based CP-ABHER-LWE scheme has greatly reduced the computation time and ciphertext size as compared to circuit based approach. Subsequently, the proposed CP-ABHER-LWE scheme was proven secure under a selective-set model with the hardness of Decision Ring-LWEd,q,ई problem

Rationality and Efficient Verifiable Computation

In this thesis, we study protocols for delegating computation in a model where one of the parties is rational. In our model, a delegator outsources the computation of a function f on input x to a worker, who receives a (possibly monetary) reward. Our goal is to design very efficient delegation schemes where a worker is economically incentivized to provide the correct result f(x). In this work we strive for not relying on cryptographic assumptions, in particular our results do not require the existence of one-way functions. We provide several results within the framework of rational proofs introduced by Azar and Micali (STOC 2012).We make several contributions to efficient rational proofs for general feasible computations. First, we design schemes with a sublinear verifier with low round and communication complexity for space-bounded computations. Second, we provide evidence, as lower bounds, against the existence of rational proofs: with logarithmic communication and polylogarithmic verification for P and with polylogarithmic communication for NP. We then move to study the case where a delegator outsources multiple inputs. First, we formalize an extended notion of rational proofs for this scenario (sequential composability) and we show that existing schemes do not satisfy it. We show how these protocols incentivize workers to provide many ``fast\u27\u27 incorrect answers which allow them to solve more problems and collect more rewards. We then design a d-rounds rational proof for sufficiently ``regular\u27\u27 arithmetic circuit of depth d = O(log(n)) with sublinear verification. We show, that under certain cost assumptions, our scheme is sequentially composable, i.e. it can be used to delegate multiple inputs. We finally show that our scheme for space-bounded computations is also sequentially composable under certain cost assumptions. In the last part of this thesis we initiate the study of Fine Grained Secure Computation: i.e. the construction of secure computation primitives against ``moderately complex adversaries. Such fine-grained protocols can be used to obtain sequentially composable rational proofs. We present definitions and constructions for compact Fully Homomorphic Encryption and Verifiable Computation secure against (non-uniform) NC1 adversaries. Our results hold under a widely believed separation assumption implied by L ≠NC1 . We also present two application scenarios for our model: (i) hardware chips that prove their own correctness, and (ii) protocols against rational adversaries potentially relevant to the Verifier\u27s Dilemma in smart-contracts transactions such as Ethereum

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

Fine-Grained Access Control Systems Suitable for Resource-Constrained Users in Cloud Computing

For the sake of practicability of cloud computing, fine-grained data access is frequently required in the sense that users with different attributes should be granted different levels of access privileges. However, most of existing access control solutions are not suitable for resource-constrained users because of large computation costs, which linearly increase with the complexity of access policies. In this paper, we present an access control system based on ciphertext-policy attribute-based encryption. The proposed access control system enjoys constant computation cost and is proven secure in the random oracle model under the decision Bilinear Diffie-Hellman Exponent assumption. Our access control system supports AND-gate access policies with multiple values and wildcards, and it can efficiently support direct user revocation. Performance comparisons indicate that the proposed solution is suitable for resource-constrained environment