Keeper: certifying research data combining Seafile and blockchain technology

<!--HTML-->The Max Planck Society runs a customized installation of Seafile called KEEPER (https://keeper.mpdl.mpg.de/) for its scientists which offers the possibility to certify research data with or without metadata by leveraging on blockchain technology. Snapshot data and a certificate representing the data on the blockchain are stored on application side and presented to the user. This implementation is tailored to our scientists and stores transaction data via a publicly available API on bloxberg, the blockchain run by a association of worldwide research institutions (https://bloxberg.org/). We would like to showcase the implementation and its potential benefits for the CS3 community.