Seed Trust & Confidence

Using seeds to build out trust rankings

EigenTrust lets applications or services calculate trust scores tailored for a specific peer. For example, the trust opinions of peer’s immediate network neighbors and vicinity may matter more to the peer. Also, services may place context-specific trust in certain peers, e.g. those who share a common and/or clandestine relationship with the service.

To accommodate these use cases, EigenTrust lets services boost the importance of these pre-trusted peers, so that the opinions of their own matter more (and those of their vicinity too, the closer the stronger boost). For this, in addition to the local trust values for all peers in the network, EigenTrust accepts two more inputs:

• The seed trust that a peer and/or service places in certain other pre-trusted peers.

• The seed confidence—the strength of the seed trust, expressed as a percentage.

The seed trust by a peer may be distinct from the local pairwise trust that the peer places in other peers. For example, although the local trust by a peer may be derived solely from the interactions that the peer had with other peers, the seed trust may include other peers that the peer had no experience with but nevertheless knew to be trustworthy.

Good selection of seed trust helps achieve better rankings. Without any seed trust, each peer is by default assigned an equal amount of trust level (1/n), which is less Sybil resistant. Seed trust boosts trust levels of peers directly or indirectly trusted by them, and the seed confidence decides the level of this boost. By choosing peers (and their vicinity) generally known to be prudent not to trust Sybils as seed trust, one can effectively limit the impact of the Sybils in the system.