RahasNym: Pseudonymous Identity Management System for Protecting against Linkability

Unlinkability and accountability are conflicting yet critical requirements that need to be addressed in order to preserve users' privacy as well as to protect service providers in today identity ecosystems. In this paper we present a pseudonymous identity management system in which users can carry out unlinkable on-line transactions without having to disclose their actual identity information in plain text to the service providers. At the same time, the service providers have strong assurance about the authenticity of the transactions. In our approach, users' identity is cryptographically encoded in pseudonymous identity tokens. % issued by trusted identity providers. Our system includes a lightweight policy language which enables users and service providers to express their requirements pertaining to pseudonymous identity verification and a suite of protocols based on zero-knowledge-proofs which enables the fulfillment of these requirements. We have implemented a prototype of the proposed system and carried out a security and performance analysis.