Long-term credentials like academic titles are increasingly being used in a digital format. In the first part, this thesis evaluates existing open and proprietary approaches ranging from qualified electronic signatures and e-apostilles to verified credentials for self-sovereign identities. The second part discusses and defines a set of requirements for a framework to support revocable long-term credentials. A design proposes a framework based on a combination of qualified electronic seals, a smart contract on a blockchain and an online server. A prototype is being built according to that specification. Finally, the chosen approach is evaluated by presenting and discussing it at several conferences at government hearings, standards organizations, and academic institutions. A range of questions occurred in that context and are discussed in the third part of this study. It is concluded that decentralized ledger technology can be a useful tool to verify long-term credentials that remain valid even when the issuing institution does not exist anymore.