  Many service systems rely on verifiable identity-related information of their
users. Manipulation and unwanted exposure of this privacy-relevant information,
however, must at the same time be prevented and avoided. Peer-to-peer
blockchain-based decentralization with a smart contract-based execution model
and verifiable off-chain computations leveraging zero-knowledge proofs promise
to provide the basis for next-generation, non-disclosing credential management
solutions. In this paper, we propose a novel credential on-chaining system that
ensures blockchain-based transparency while preserving pseudonymity. We present
a general model compliant to the W3C verifiable credential recommendation and
demonstrate how it can be applied to solve existing problems that require
computational identity-related attribute verification. Our zkSNARKs-based
reference implementation and evaluation show that, compared to related
approaches based on, e.g., CL-signatures, our approach provides significant
performance advantages and more flexible proof mechanisms, underpinning our
vision of increasingly decentralized, transparent, and trustworthy service
systems.
