  Increased collaborative production and dynamic selection of production
partners within industry 4.0 manufacturing leads to ever-increasing automatic
data exchange between companies. Automatic and unsupervised data exchange
creates new attack vectors, which could be used by a malicious insider to leak
secrets via an otherwise considered secure channel without anyone noticing. In
this paper we reflect upon approaches to prevent the exposure of secret data
via blockchain technology, while also providing auditable proof of data
exchange. We show that previous blockchain based privacy protection approaches
offer protection, but give the control of the data to (potentially not
trustworthy) third parties, which also can be considered a privacy violation.
The approach taken in this paper is not utilize centralized data storage for
data. It realizes data confidentiality of P2P communication and data processing
in smart contracts of blockchains.
