P2A: Privacy Preserving Anonymous Authentication Based on Blockchain and SGX

Modern Identify-as-a-Service solutions solve the problems of burdensome user credential management and non-uniform security strength, by introducing an Identity Provider (IdP) that holds the users’ identities and grants a user one-time access tokens when he/she tries to login to different online applications (known as the Relying Parties, RPs). However, the non-negligible problem of privacy leakage during authentication largely remains unattended. In this paper, we propose a Privacy Preserving Anonymous Authentication Scheme (P2A) with Blockchain and Intel Software Guard Extensions (SGX). The IdP in P2A manages the users’ identities by issuing different kinds of transactions in the Blockchain, covering the registration, update, freeze/thaw, and deletion of identities. When the user wants to login to an RP, instead of asking for an one-time token from the IdP, he can generate an identity proof locally with SGX and login to the RP with an RP-specific pseudonym (PN). By resorting to the Blockchain, the RP will be convinced that the PN is associated with some registered identity on IdP and specific attributes of the user are satisfactory, without obtaining the real identity and raw attributes of the user. In this way, privacy leakages to the IdP and RPs are eliminated. P2A has a few exciting new features and security analysis shows it can resist various attacks even under strict assumptions.