Establishing Trust with Privacy

With the advent of self-organizing systems such as ad hoc networks or ubiquitous computing, security protocols have to meet a new requirement for establishing trust among parties that have no a priori relationship like a shared naming structure or a common organization. Trust establishment in this context calls for a brand new paradigm with respect to classical scenarios whereby entities build trust based on some existing security association. We suggest in this paper a cryptographic protocol through which parties can build trust based on the history of their interactions with other parties. This protocol allows a prover to get a proof of history or the evidence that it was involved in some interaction with another party. During further interactions, other parties consider the prover trustworthy based on the verification of the proof of history. Privacy is an essential requirement for such a protocol since providing proof of history to several parties without privacy would severely expose the behavior of the prover. The history-based trust establishment protocol thus assures the anonymity of the prover and the unlinkability of interactions using the proof of history. Moreover, the prover can choose to show only parts of its history. The proof of history is based on a signature mechanism and the trust establishment protocol is a challenge-response protocol based on this mechanism. The signature mechanism is an extension of group signatures.