Why the Path to Quantum Resistance Runs Uphill for Bitcoin Wallet Makers

In brief

• Trezor is preparing for the UX challenges of a post-quantum Bitcoin, where SHRINCS, the community’s leading candidate signature scheme, lets users choose efficient “stateful” signatures that can expose funds to theft if reused beyond a signing budget, CTO Tomáš Sušánka said.
• To reduce that risk, Trezor is considering making larger, safer “stateless” signatures the default and hiding the riskier stateful option behind advanced settings.
• He also noted devices themselves need post-quantum upgrades for firmware and authentication.

Bitcoin custody has always involved some degree of risk, but wallet manufacturers like Trezor—which build physical devices designed to keep a user’s private keys secure offline—are preparing for a post-quantum world where new challenges arise.

That’s because SHRINCS, the community’s leading candidate for a post-quantum signature scheme, allows users to make transactions using stateful signatures that require rigid state tracking to prevent funds from being stolen, according to Trezor CTO Tomáš Sušánka.

Proposed late last year by Blockstream Research Director Jonas Nick and cryptographer Mikhail Kudinov, SHRINCS centers on a composite hash-based approach: users can make transactions using either stateful signatures or stateless signatures.