- From the four types of processors that we initially considered we primarily focused on three options: Secure Element (SE), System on Chip (SoC), and Microcontroller (MCU).
- While we are lucky to have a silicon design team here at Block that could build a custom chip for this product, these weren’t the right tradeoffs for our first product.
- The Silicon Labs EFR32MG24 secure MCU offered the most compelling mix of security features and gave us the most flexibility for transparency. The EFR32MG24 boasts an impressive range of security protections, is based on the ARM Cortex-M33 architecture, and comes with standard controls such as TrustZone®, which helps isolate security-sensitive code.
- The EFR32MG24 features a separate core for storing and using keys, encrypted by a PUF, which means the root plaintext secret key doesn't even need to exist within the device while it's powered off. The chip also includes fault injection and side-channel countermeasures, which helps secure the wallet even if it is in an attacker’s hands. Moreover, the chip offers cryptographic acceleration for a wide range of useful algorithms.
- We intend to open-source as much of our firmware and hardware design as possible. This helps others verify that the hardware does what we claim - and only what we claim. Furthermore, we believe that inviting scrutiny is critical for security, and an open design and codebase encourages that.