PrivSSO: Practical Single-sign-on Authentication against Subscription/Access Pattern Leakage

Single-sign-on (SSO) authentication employs an identity provider (IdP) to provide users with an efficient way to authenticate themselves with different service providers and has been widely applied in digital systems. However, existing SSO authentication schemes suffer from critical issues in terms of security and privacy. Regarding security, most SSO authentication schemes achieve a high convenience at the expense of security and are thereby susceptible to various attacks. Regarding privacy, most existing schemes fail to protect users' subscription pattern and access pattern against adversaries who can easily extract users' sensitive information from their authentications and launch subsequent attacks for profits. In this paper, we develop a practical SSO authentication system, dubbed PrivSSO, with the protection of users' subscription pattern and access pattern. To balance the trade-off between security and convenience, the key technique is a secure "hybrid" key-based authentication mechanism: a long-term key stored in a well-guarded hardware token serves as the "primary" authentication factor (AF) to guarantee strong security; an ephemeral key bound with portable device(s) serves as the "daily-used" AF to achieve high convenience. To protect the subscription pattern and access pattern from leakage, we propose a redactable token generation mechanism, where the users themselves specify what IdP and the service providers can learn from their authentications. We formally define and prove the security of PrivSSO. We also implement a PrivSSO prototype and conduct a comprehensive performance evaluation to demonstrate its practicality.