Firmware updates in IoT pose a new set of security risks. Secure bootloaders can be handy to deploy new versions of the firmware on those devices that are only reachable through a remote connection. wolfBoot is a portable, GPL, OS-agnostic, secure bootloader solution for 32-bit microcontrollers, relying on wolfCrypt for firmware authentication, providing secure firmware update mechanisms. Due to the minimalist design of the bootloader and the tiny HAL API, wolfBoot is completely independent from any OS or bare-metal application, and can be easily ported and integrated in existing embedded software projects to provide a secure firmware update mechanism. This presentation will focus on the implementation details and the design choices of the project, and the porting done to ARM Cortex-M and RISCV32 microcontrollers.