This paper provides an overview of the Self-Sovereign Identity (SSI) concept, focusing on four different components that we identified as essential to the architecture. Self-Sovereign Identity is enabled by the new development of blockchain technology. Through the trustless, decentralised database that is provided by a blockchain, classic Identity Management registration processes can be replaced. We start off by giving a simple overview of blockchain based SSI, introducing an architecture overview as well as relevant actors in such a system. We further distinguish two major approaches, namely the Identifier Registry Model and its extension the Claim Registry Model. Subsequently we discuss identifiers in such a system, presenting past research in the area and current approaches in SSI in the context of Zooko's Triangle. As the user of an SSI has to be linked with his digital identifier we also discuss authentication solutions. Most central to the concept of an SSI are the verifiable claims that are presented to relying parties. Resources in the field are only losely connected. We will provide a more coherent view of verifiable claims in regards to blockchain based SSI and clarify differences in the used terminology. Storage solutions for the verifiable claims, both on-and off-chain, are presented with their advantages and disadvantages.

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Abstract. Object calculi have been investigated as semantical foundation for object-oriented languages. Often, they are object-based, whereas the mainstream of object-oriented languages is class-based. Considering classes as part of a component makes instantiation a possible interaction between component and environment. As a consequence, one needs to take connectivity information into account. We formulate an operational semantics that incorporates the connectivity information into the scoping mechanism of the calculus. Furthermore, we formalize a notion of equivalence on traces which captures the uncertainty of observation cause by the fact that the observer may fall into separate groups of objects. We use a corresponding trace semantics for full abstraction wrt. a simple notion of observability. This requires to capture the notion of determinism for traces where classes may be instantiated into more than one instance during a run and showing thus twice an equivalent behavior (doing a "replay"), a problem absent in an object-based setting.

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