Blockchain is a promising solution for Industry 4.0 due to its traceability and immutability. However, blockchain itself does not guarantee the input data integrity. The tampered data from an endpoint device can be a significant problem because it may result in a cascaded negative effect on the whole smart factory operations. In this paper, we propose an FPGA-based private blockchain system for IIoTs, where the transaction generation is performed inside the FPGA in an isolated and enclaved manner. For the key confidentiality and transaction integrity, the proposed system utilizes a PUF, soft processor, and tightly coupled sensor connections inside the FPGA fabric. Since all the critical operations are hidden under the hood, adversaries even with the root privilege cannot intervene in the transaction generation process. The implemented IIoT device provides 33 transactions per minute and consumes a 191 mW of power
