Privacy Protection (GDPR)
The core definition of the blockchain technology is a "public bulletin board" where everyone in the network has the identical data. Hence, it is not wise, or even logical, to create blocks that consist of privacy sensitive data such as financial or medical data. On the one hand, there is a need for sharing sensitive data and on the other hand, sensitive data cannot be shared. This dilemma can be solved by building a second layer on top of the blockchain, using cryptographic constructions, namely Zero-Knowledge Proofs (ZKPs).