Executable Trust: A Formal Model and Architecture for Verifiable Digital Interactions

Digital trust in online interactions is commonly established through mechanisms such as decentralized identifiers (DIDs), verifiable credentials (VCs), and digital wallets. While these technologies ensure the correctness of individual components, they do not guarantee that an interaction as a whole is trustworthy. This limitation arises because real-world interactions consist of sequences of dependent steps, where inconsistencies may occur even when each step is locally valid. In this paper, we introduce the concept of executable trust, which models trust as a verifiable property of execution across interaction steps. We formalize interactions as sequences of TrustEvidence objects that capture both step-level validity and cross-step dependencies. Based on this model, we demonstrate that step-level correctness is insufficient to guarantee interaction-level trust, and we derive a minimal and sufficient condition for establishing end-to-end trust through composable verification and consistency constraints. We further present the Executable Trust Architecture (ETA), which operationalizes the proposed model through components for evidence generation, constraint enforcement, secure communication, and auditability. The feasibility and effectiveness of the approach are validated through scenario-based evaluations covering key trust properties, including authenticity, integrity, privacy, and accountability. The proposed approach provides a systematic foundation for verifying trust in complex digital interactions and supports the design of systems in which trust can be explicitly enforced, evaluated, and audited at runtime.