The security of a System-on-Chip depends on various tamper protections used to protect the cryptographic keys from different kind of attacks. These keys are usually transmitted as plaintext between heterogonous modules through a SoC interconnect as bus and network-on-chip.
Advance probing techniques consist in approaching probes near an on-chip wire and observe logical values transmitted through it. This technique is applied when the on-chip wire is routed on the top metal layers of the chip. Another technique, based on the Focused on Beam (FIB) technology, consists of drilling a hole to an on-chip wire routed on bottom metal layers, felling the hole with platinum and creating a pad on surface for easy access.
The probing attacks are expensive but they are more and more used by attackers to retrieve the keys transmitted through the SoC interconnect. Advance probing attacks might use multiple probes and access to full data word carried by the bus. This is why busses should be protected against probing attacks.
The typical protection against the probing attacks is shielding using dedicated wires routed above the buses to be protected. The shield protection deteriorates the chip performances in term of area and power consumption when the shield lines cover the whole circuit. To reduce the shield cost, the designer can select only sensitive zones of the chip to be covered with the shield; however, this solution introduces a breach because the buses that transmit sensitive data between the zones covered by the shield remain vulnerable.
Scrambled Bus IP masks all data carried on the bus with random variables generated locally by cryptographic primitives.