In a reputation based trust network, each peer stores trust information of others and answers the trust queries, in addition to providing services to others. We present a cryptographic protocol on Chord, which provides anonymous access to trust information. Peers form anonymity groups and generate responses inside the group. Responder of a trust query has k-anonymity protection against an adversary who can sniff all communication on the network. Moreover, our encryption scheme ensures that the initiator of a trust query can check the validity of an anonymous reply.