AASSI: A Self-Sovereign Identity Protocol With Anonymity and Accountability

The concern and opposition to centralized management of user identities by third-party authorities have led to the emergence of Self-Sovereign Identity (SSI). With the help of blockchain, SSI effectively restore users’ control over their own identities, but privacy concerns due to blockchain transparency, coupled with the absence of accountability like Know Your Customer (KYC) and Anti-Money Laundering (AML), have cast uncertainties upon the viability of SSI. In this paper, we bridge this gap by introducing AASSI, a pioneering SSI protocol meticulously designed to balance the twin imperatives of privacy and accountability. Specifically, AASSI extends support for anonymity, self-derivation, fine-grained tracing and selective revocation. In the realm of anonymity and self-derivation, AASSI introduces redactable signatures, which empowers users to autonomously derive distinctive credentials for each user-service-provider interaction, effectively improving privacy protection and self-management capabilities. Pertaining to fine-grained tracing, the protocol employs a dual-tag system that facilitates tracing users’ real identities as well as a granular historical records of derived credentials. For selective revocation, AASSI leverages dynamic accumulators as a building block to enable the revocation of offending users. Ultimately, we provide functional comparison, which shows that AASSI has robust features, in particular, it supports novel self-derived features that further increase user control over their identity, and fine-grained tracking, which provides more flexibility for tracers. We demonstrate protocol efficiency through off-chain time-consuming comparison, which show that AASSI dramatically reduces the time overhead of credential verification. Moreover, We test the on-chain communication overhead and experimentally prove the feasibility of AASSI.