A survey charting trust models and systems in self-sovereign identity

Self-Sovereign Identity (SSI) is widely positioned as the decentralized future of digital identity. However, although traditional SSI literature emphasizes architecture and privacy, it largely overlooks a systematic analysis of how trust is formed, propagated, and managed. Trust is fundamental because, without it, the actions performed by key actors, including credential issuers, lose much of their practical value. In this landscape, trust is the ground on which SSI systems stand; when that ground is absent or unstable, any structure built on it crumbles. Against this backdrop, we chart the landscape of trust through a comprehensive survey of Trust Models (TMs) and Trust Management Systems (TMSs) in SSI. At the abstract level, we analyze TMs by examining the types of trust relationships among SSI actors and how trust is defined and represented. At the implementation level, we discuss TMSs in terms of how trust is represented, stored, and protected in the systems proposed in the literature. We analyzed 26 sources (24 peer-reviewed papers plus the Sovrin whitepaper and governance framework document), consolidated into 24 approaches, benchmarking 16 features across these dimensions. Based on this analysis, we identify five open challenges: enabling cross-chain trust portability; designing a hybrid TM that blends Web of Trust and hierarchies; supporting heterogeneous actors such as IoT devices and humans; implementing privacy-preserving feedback mechanisms; and TM and TMS interoperability in emerging settings, including delegated AI agents. Our analysis offers a compass to guide researchers and developers in selecting trust models and advancing SSI systems.