Figure 13(a). This integrated hard- ware implements a dedicated hard- ware accelerator for the first-factor authentication based on symmetric cryptography, a touch detection cir- cuit for the second-factor tap recog- nition, and a wake-up detector. To securely authenticate an implant- able drug delivery system, the chip was integrated into a system dem- onstration powered by a battery. This system detects patterns via a force-sensitive resistor and commu- nicates wirelessly with the external relay device for authentication. The authentication protocol takes 660 ms when only the first-factor authenti- cation is performed and 12 s when User 1 the second-factor authentication is also enabled, while consuming only 8 nW of active power from an 0.87-V supply for the DTL S-PSKb a s e d first-factor authentication. Fig--ure 13(b) depicts the measured system protocol waveforms in the course of operation. Authenticated Wireless Power Near-field wireless charging has re- cently become the widely preferred method to charge IoT devices in our daily lives. However, to harm the per- formance of critical tasks performed by IoT devices, an adversary can ex- ploit this wireless charging capability by counterfeiting the charger. This ex- IMD ample [26] addresses the protection of IoT devices with a resonant wireless recharging feature from harsh tran- sients imposed by counterfeit wireless chargers. Several other works [27], [28] demonstrated the authentication of a wired charger for the safety of the battery via symmetric-key protocols. The growing number of wireless-pow- ered IoT devices makes it challenging to use a PSK for the symmetric-key protocols suitable for one-charger and one-receiver (IoT device) pair au- thentication. Preprogramming all of the private keys of possible chargers with which the device can interact is not a scalable solution. An alternative solution is to exchange a secret key Server Controller (Cellphone) Wake Up IMD Using Four Taps Bluetooth Connection 3 2 Establish Connection Internet Connection User Sends Command to Server Through Cellphone App Server IMD 4 First-Factor Authentication DTLS-PSK Handshake and Authentication of IMD Establishment of Encrypted Channel 5 Second-Factor Authentication IMD Server Command + Second-Factor Code Second-Factor Code: (3, 1, 4) Taps User Taps According to Code Server Sends Text Message to User Verification Result Acknowledgment 6 Drug Delivery (After Successful Dual-Factor Authentication) FIGURE 12: The dual-factor authentication protocol exploiting a touch-based voluntary human action for authentication of an IMD [25]. 74 FA L L 2 0 2 0 IEEE SOLID-STATE CIRCUITS MAGAZINE