  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.
