Schemes for multi-party trust computation are presented. The schemes do not make use of a Trusted Authority. The schemes are more efficient than previous schemes in terms of the number of messages exchanged, which is proportional to the number of participants rather than to its square. We note that in our schemes the length of each message may be larger than the message length typically found in previously published schemes. The calculation of a trust, in a specific user by a group of community members starts following a request by an initiator. The trust computation is provided in a completely distributed manner, where each user calculates its trust value privately and independently. Given a community C and its members (users) U 1 , . . . , U n , we present computationally secure schemes for trust computation. The first scheme, Accumulated Protocol AP computes the average trust attributed to a specific user, U t following a trust evaluation request initiated by a user U n . The exact trust values of each queried user are not disclosed to U n . The next scheme, Weighted Accumulated Protocol WAP generates the average weighted trust in a specific user U t taking into consideration the unrevealed trust that U n has in each user participating in the trust evaluation process. The Public Key Encryption Protocol PKEP outputs a set of the exact trust values given by the users without linking the user that contributed a specific trust value to the trust this user contributed. The obtained vector of trust values assists in removing outliers. Given the set of trust values, the outliers that provide extremely low or high trust values can be removed from the trust evaluation process. We extend our schemes to the case when the initiator, U n , can be compromised by the adversary, and we introduce the Multiple Private Keys and the Weighted protocols (MPKP and MPWP) for computing average unweighted and weighted trust, respectively. Moreover, the Commutative Encryption Based Protocol (CEBP) extends the PKEBP in this case. The computation of all our algorithms requires the transmission of O(n) (possibly large) messages.
Keywords: Private trust computations; Multi-party computations; Anonymity
Our contributionThe purpose of this paper is to introduce new schemes for decentralized reputation systems. These schemes do not make use of a Trusted Authority to compute the trust in a particular user that is attributed by a community of users. Our objective is to compute trust while preserving user privacy.We present new efficient schemes for calculating the trust in a specific user by a group of community members upon the request of an initiator. The trust computation is © 2014 Dolev et al.; licensee Springer. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Dolev et al. Journal of Trust Management2014, 1:8 Pa...