Analyzing Interoperability and Portability Concepts for Self-Sovereign Identity

The Self-Sovereign Identity (SSI) paradigm postulates global unique identities that are controlled by the user. To achieve a widespread applicability, the emphasized interoperability principle supports the proclaimed ambition. Furthermore, identity portability enables the transfer of the identity to another SSI solution. These axioms gain additional momentum due to the development of numerous implementations. In this paper, we examine interoperability and portability concepts for SSI. Initially, we define these principles regarding the blockchain-based SSI model. Subsequently, we outline assessment criteria considering functional scope, governance/ trust, scalability and further characteristics. For interoperability, we evaluate the concepts of protocol and standard, broker, hub and pairing. Besides that, we assess the transformer and auxiliary solutions for portability. We can conclude that all interoperability schemes provide the maximum functional level theoretically. In contrast, portability patterns are fragmented in this regard. Nonetheless, protocol and standards can only be applied in the design phase, whereas broker, hub, pairing, transformer and auxiliary solutions enable interoperability, respectively portability post-deployment of the SSI system.