Looking Under the Hood of Z-Wave: Volatile Memory Introspection for the ZW0301 Transceiver

Z-Wave is a proprietary Internet of Things substrate providing distributed home and office automation services. The proprietary nature of Z-Wave devices makes it difficult to determine their security aptitude. While there are a variety of open source tools for analyzing Z-Wave frames, inspecting non-volatile memory, and disassembling firmware, there are no dynamic analysis tools allowing one to inspect the internal state of a Z-Wave transceiver while it is running. In this work, a memory introspection capability is developed for three Z-Wave devices containing a ZW0301, a Z-Wave transceiver system-on-chip. In all three devices, the firmware image is modified to include the memory introspection capability by hooking an existing data exfiltration mechanism used by the device. The memory introspection capability is applied to determine how nonces are generated by Z-Wave devices to prevent replay attacks. Through a combination of static and dynamic analysis, the nonce generating algorithm is found to be based on a nonce round key that updates every secure frame transaction.