#741: Solving The Wrench Attack with Max Guise

Max Guise, head of BitKey at Block, discusses the company's approach to Bitcoin self-custody through its hardware wallet system. The conversation centers on the new BitKey device, which builds on prior versions by adding on-device verification while maintaining seedless setup, collaborative multisig, and recovery tools. Guise explains design decisions driven by user research, tradeoffs in security and privacy, and Block's push to make Bitcoin practical for daily use.

Core Design Choices for Self-Custody

BitKey targets barriers to self-custody like complex setup, seed phrase management, and recovery risks. It uses a 2-of-3 multisig with one key on the hardware, one on the mobile app, and one held by Block servers—avoiding seed phrases entirely. Onboarding takes minutes: users unbox, enroll biometrics (fingerprint), add recovery contacts, and transact immediately. Recovery options cover losing phone or hardware (use remaining keys), both (recovery contacts), or Block shutdown (emergency exit kit). Guise notes the invisible complexity: the system handles edge cases like interrupted onboarding, app/firmware version changes, or partial device loss without user intervention. This hides complexity to prioritize safety, ease, and sovereignty.