TOTP-Based Open Hardware Authenticator Powered by an ESP32 Microcontroller

Some people like to use hardware authenticators or security keys when working with public or company computers to keep their data private, certainly so when hackers can easily steal unprotected information. There are many great authenticators on the market that can be had for cheap, but others such as developer Vedant Parajape have designed their own platforms using readily-available hardware. Parajape became interested in authenticators after seeing his dad’s security keys and wondered how they could generate code without being connected to a network.

“I fired up google and tried to search about it, and surprisingly it used a pretty amazing concept. It had a shared key with the server, and then it did some computation on the shared key and current UTC time to get a 6-digit number. So, the remote device just had to be accurate at timekeeping,” Parajape noted in his project log. He then took that information and designed his initial Open Authenticator prototype using a development kit he had on hand and an ESP32 module. It worked well enough, but he wanted a more streamlined platform, similar to RSA’s SecureID Key FOB.

Parajape succeeded on a second prototype that’s much more compact and places all of the hardware components on a single PCB, sans a connected 0.96" OLED. The latest revision of the Open Authenticator packs an ESP32-WROOM-32D module, a DS3231 RTC with battery backup (CR2032) for timekeeping, a 3.7V 300mAh LiPo battery, and an MCP73831 for charging.

The setup also features a TPS63001 buck-boost converter IC for an efficient 3.3V power supply with an input range from 1.8V to 5.5V, a TPS22919 load switch to control power to the OLED and RTC chip, and a USB Type-C port to recharge the unit. Parajape has uploaded a detailed walkthrough of the Open Authenticator for those interested in recreating his build.