HWI reloaded: Current state of hardware wallets and how to build a common interface for them
An exploration of the modern hardware wallet landscape and the technical approaches for creating unified interfaces across different devices and platforms. What You'll Learn: This talk begins with the fundamentals—examining the threat model that hardware wallets address and diving into the technical components that make them secure, including secure elements and communication systems that protect your private keys. The session explores why cross-compatibility has become essential in today's ecosystem, particularly for multisig implementations, and examines the evolving standards like PSBT (Partially Signed Bitcoin Transactions) and BIP 388 that enable seamless interoperability. The core focus is a comprehensive implementation overview of common interface approaches. This deep dive traces the evolution from Bitcoin Core's original HWI through WizardSardine's async-hwi improvements, culminating in bhwi—the latest advancement that builds upon lessons learned from both predecessors. The presentation examines architectural decisions, compares approaches, and extracts practical patterns for building robust hardware wallet interfaces that work across multiple devices and platforms. This session is designed for developers building wallet software, hardware wallet manufacturers, and technical professionals looking to implement or improve hardware wallet integration in their projects.