  PCBs are the core components for the devices ranging from the consumer
electronics to military applications. Due to the accessibility of the PCBs,
they are vulnerable to the attacks such as probing, eavesdropping, and reverse
engineering. In this paper, a solution named EOP is proposed to migrate these
threats. EOP encrypts the inter-chip communications with the stream cipher. The
encryption and decryption are driven by the dedicated clock modules. These
modules guarantee the stream cipher is correctly synchronized and free from
tampering. Additionally, EOP also incorporates the PCB-level obfuscation for
protection against reverse engineering. EOP is designated to be accomplished by
utilizing the COTS components. For the validation, EOP is implemented in a Zynq
SoC based system. Both the normal operation and tampering detection performance
are verified. The results show that EOP can deliver the data from one chip to
another without any errors. It is proved to be sensitive to any active
tampering attacks.
