Identity Escrow Protocol and Anonymity Analysis in the Applied Pi-Calculus

Anonymity with identity escrow attempts to allow users of an online service to remain anonymous, while providing the possibility that the service owner can break the anonymity in exceptional circumstances, such as to assist in a criminal investigation. In the article, we propose an identity escrow protocol that distributes user identity among several escrow agents. The main feature of our scheme is it is based on standard encryption algorithms and it provides user anonymity even if all but one escrow holders are dishonest acting in a coalition. We also present analysis of the anonymity property of our protocol in the applied pi-calculus. We review a related scheme by Marshall and Molina-Jiminez [2003] that aimed to achieve goals similar to ours, and show that their scheme suffers from serious weaknesses.