Anchorage Digital says it can move two-thirds of Bitcoin to post-quantum signatures without exposing private keys

Anchorage Digital, a federally chartered crypto bank, published Post-Quantum Turnstile, a STARK-based framework (STARKs are a proof system that lets one party prove a statement without revealing the secret) that lets legacy Bitcoin holders migrate signing authority to post-quantum cryptography, cryptography designed to resist attacks by future quantum computers. Anchorage says the framework can move roughly two-thirds of circulating Bitcoin, the coins whose public keys already sit exposed on-chain and are therefore the most quantum-vulnerable legacy supply, without exposing private or public key material during the migration.

The plan targets two threats: Shor's algorithm, a quantum routine that can break Bitcoin's current public-key cryptography, and the "harvest now, decrypt later" model, where adversaries record today's encrypted traffic to decrypt later with a future quantum computer. The approach moves signing authority, not balances, to post-quantum keys.

The broader strategy also lists three deployed safeguards: hash-based address conventions that keep dormant BTC quantum-safe at rest, hybrid post-quantum TLS for internal and managed ChromeOS devices, and an "agile HSM" (hardware security module) architecture whose firmware can adopt new NIST-finalized signature standards without a system overhaul. NIST, the U.S. National Institute of Standards and Technology, has not finalized SQIsign in its current PQC set. Anchorage calls the "agile HSM" framing its own.

The release includes sqisign-rs, a Rust SQIsign implementation benchmarked at roughly seven times smaller than Falcon, a NIST-track post-quantum signature scheme. That comparison is Anchorage's own. Full details: Anchorage's release and technical paper.