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 by the number of messages exchanged which is proportional to the number of participants rather than to a quadratic number of the participants. We note that in our schemes the length of each message may be larger than the message length of previous schemes. The calculation of a trust, in a specific user by a group of community members, starts upon a request of an initiating user. The trust computation is provided in a completely distributed manner, while each user calculates its trust value privately. Given a community C and its members (users) U_1,..., U_n, we present computationally secure schemes for trust computation. The first Accumulated Protocol AP computes the average trust in a specific user U_t upon the 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 Weighted Accumulated protocol WAP generates the average weighted trust in a specific user Ut taking into consideration the unrevealed trust that U_n has in each user participating in the trust process evaluation. We extend our schemes to the case when the initiating user U_n can be compromised by the adversary, and we introduce the Multiple Private Keys MPKP and the Multiple Private Keys Weighted MPWP protocols for computing average unweighted and weighted trust, respectively. The computation of all our algorithms requires the transmission of O(n) (possibly large) messages.
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