  Self-sovereign Identity (SSI) powered by distributed ledger technologies
enables more flexible and faster digital identification workflows, while at the
same time limiting the control and influence of central authorities. However, a
global identity solution must be able to handle myriad credential types from
millions of issuing organizations. As metadata about types of digital
credentials is readable by everyone on the public permissioned ledger with
Hyperledger Indy, anyone could find relevant and trusted credential types for
their use cases by looking at the records on the blockchain. To this date, no
efficient full-text search mechanism exists that would allow users to search
for credential types in a simple and efficient fashion tightly integrated into
their applications. In this work, we propose a full-text search framework based
on the publicly available metadata on the Hyperledger Indy ledger for
retrieving matching credential types. The proposed solution is able to find
credential types based on textual input from the user by using a full-text
search engine and maintaining a local copy of the ledger. Thus, we do not need
to rely on information about credentials coming from a very large candidate
pool of third parties we would need to trust, such as the website of a company
displaying its own identifier and a list of issued credentials. We have also
proven the feasiblity of the concept by implementing and evaluating a prototype
of the full-text credential metadata search service.
