VCTP: A Verifiable Credential-based Trust Propagation Protocol for Personal Issuers in Self-Sovereign Identity Platforms

TL;DR

This paper introduces VCTP, a protocol enabling individual users to be trusted verifiable issuers in SSI platforms by leveraging trust propagation credentials and blockchain, enhancing trust without central authorities.

Contribution

It proposes a novel trust propagation protocol for individual issuers in SSI, combining sanitizable signatures and voting to establish trust without central authorities.

Findings

The protocol is practical and effective under different system loads.

It enhances trust support for individual issuers in SSI platforms.

The implementation demonstrates good performance and scalability.

Abstract

Self Sovereign Identity (SSI) is an emerging identity system that facilitates secure credential issuance and verification without placing trust in any centralised authority. To bypass central trust, most SSI implementations place blockchain as a trusted mediator by placing credential transactions on-chain. Yet, existing SSI platforms face trust issues as all credential issuers in SSI are not supported with adequate trust. Current SSI solutions provide trust support to the officiated issuers (e.g., government agencies), who must follow a precise process to assess their credentials. However, there is no structured trust support for individuals of SSI who may attempt to issue a credential (e.g., letter of consent) in the context of business processes. Therefore, some risk-averse verifiers in the system may not accept the credentials from individual issuers to avoid carrying the cost of mishaps from potentially inadmissible credentials without reliance on a trusted agency. This paper proposes a trust propagation protocol that supports individual users to be trusted as verifiable issuers in the SSI platform by establishing a trust propagation credential template in the blockchain. Our approach utilises (i) the sanitizable signature scheme to propagate the required trust to an individual issuer, (ii) a voting mechanism to minimises the possibility of collusion. Our implementation demonstrates that the solution is both practical and performs well under varying system loads.