D2D PHY stands for Die-to-Die Physical Layer. It is the electrical and timing interface that lets separate silicon dies, often in a chiplet package, exchange data at very high speed. The PHY defines signaling, lane alignment, clock recovery, voltage levels, and error handling so the dies can communicate reliably across a tiny package-level link.
In cyber security, D2D PHY matters because modern systems increasingly split trusted logic, memory, and accelerators across multiple dies. That creates new attack surfaces in the package: signal integrity faults, fault injection, probing, and implementation bugs in the interconnect can all affect confidentiality or integrity. Defenders care about D2D PHY design because secure packaging, link encryption, integrity checks, and robust error detection help protect chiplet-based platforms from tampering and data leakage.