A Quantifiable Trust Model for Blockchain-based Identity Management

Removing the need for a trusted third party, blockchain technology revolutionizes the field of identity management. Service providers rely on digital identities to securely identify, authenticate and authorize users to their services. Traditionally, these digital identities are offered by a central identity provider belonging to a specific organisation. Trust in the digital identity mainly originates from the identity provider's reputation, organizational functioning and contractual obligations. Blockchain technology enables the creation of decentralized identity management without a central identity provider as trusted third party. Therefore, the derivation of trust in digital identities within this paradigm requires a distinct approach. In this paper we propose a novel general quantifiable trust model and a specific implementation variant for blockchain-based identity management. Applying the model, trust is deduced in a decentralized manner from attestations of claims and applied to the associated digital identity. This concept replaces trust with a central identity provider by aggregated trust into attestation issuers. Thus, promoting self-sovereign identities to be fit for purpose. The calculated numerical trust metric serves as independent basis for the definition of assurance levels to simplify and automate reasoning about trust by service providers without requiring a dedicated evaluation of a trusted third party.