Ngoc Hong Tran¹, Tri Nguyen², Quoc Binh Nguyen³, Susanna Pirttikangas², M-Tahar Kechadi^4,5, ¹Vietnamese-German University, Vietnam, ²University of Oulu, Finland, ³Ton Duc Thang University, Vietnam, ⁴University College Dublin, Ireland, ⁵Insight Centre for Data Analytics, University College Dublin, Ireland

This paper investigates the situation in which exists the unshared Internet in specific areas while users in there need instant advice from others nearby. Hence, a peer-to-peer network is necessary and established by connecting all neighbouring mobile devices so that they can exchange questions and recommendations. However, not all received recommendations are reliable as users may be unknown to each other. Therefore, the trustworthiness of advice is evaluated based on the advisor's reputation score. The reputation score is locally stored in the user’s mobile device. It is not completely guaranteed that the reputation score is trustful if its owner uses it for a wrong intention. In addition, another privacy problem is about honestly auditing the reputation score on the advising user by the questioning user. Therefore, this work proposes a security model, namely Crystal, for securely managing distributed reputation scores and for preserving user privacy. Crystal ensures that the reputation score can be verified, computed and audited in a secret way. Another significant point is that the device in the peer-to-peer network has limits in physical resources such as bandwidth, power and memory. For this issue, Crystal applies lightweight Elliptic Curve Cryptographic algorithms so that Crystal consumes less the physical resources of devices. The experimental results prove that our proposed model performance is promising.

Reputation, peer to peer, privacy, security, homomorphic encryption, decentralized network.