Crypto custodian Coinbase, which holds approximately 5% of all BTC, published a technical post on October 13 specifying the necessary standards for Bitcoin to transition to post-quantum signature schemes. The company emphasized that adopting new digital signatures must fit within Bitcoin's limited block space while remaining viable for major custodians and self-custody wallets alike.
Key Takeaways:
- Coinbase holds roughly 5% of the circulating BTC supply.
- The company supports output structures like P2MR (BIP-360) and P2TRv2 for future upgrades.
- Candidates for post-quantum signatures include ML-DSA, prospective FN-DSA, and SHRINCS.
- Transition proposals include BIP-361 by Jameson Lopp and a canary address mechanism by BitMEX Research.
Evaluating Technical Criteria and Signature Risks
To prepare for quantum computing risks, Coinbase is convening discussions with developers and supporting open-source initiatives through the Bitcoin Security Consortium. It highlighted P2MR (proposed in BIP-360) and P2TRv2 as potential output scripts capable of accommodating new cryptographic methods without requiring repeated structural overhauls. The exchange also suggested implementing hybrid schemes, enabling wallets to spend funds via conventional ECDSA or Schnorr signatures, or alternatively via post-quantum keys during the migration phase.
However, Coinbase expressed strong caution regarding stateful post-quantum signature designs. While stateful options offer smaller sizes and faster verification than stateless alternatives, reuse of signing state can allow message forgery. The exchange warned that recovering from failed updates or lost state creates operational hazards for platforms running multi-party computation (MPC) setups or multiple signing servers. Evaluation criteria outlined by the exchange focus on signature size, verification speed, transaction fees, full-node workload, hardware wallet compatibility, and MPC integration. Technical candidates listed for review include ML-DSA, FN-DSA, and SHRINCS.
Debate Over Unmigrated Funds and Address Freezes
The transition strategy also raises contentious questions regarding inactive wallets. Under BIP-361, proposed by Jameson Lopp alongside five other developers, Bitcoin would first restrict transactions sent to quantum-vulnerable addresses, subsequently block legacy signatures from spending, and potentially establish a third recovery phase after deadlines pass. Opponents argue that protocol-enforced spending freezes violate Bitcoin's core principles of censorship resistance and self-sovereignty.
As an alternative, BitMEX Research floated a canary mechanism in April. This framework would trigger address freezes only if funds leave a designated address with an unknown private key, serving as cryptographic proof that a quantum entity has successfully cracked legacy keys. Building on Coinbase's post-quantum Bitcoin defense initiative, these technical discussions highlight the delicate balance between securing user assets and preserving network rules.
Why It Matters
Securing Bitcoin against quantum computing threats is one of the most complex engineering challenges facing the ecosystem, given the strict need to preserve backwards compatibility and decentralization. As a major custodian holding 5% of all BTC, Coinbase is pushing for consensus before quantum hardware becomes a practical threat. How the developer community handles unmigrated addresses will test whether Bitcoin can protect vulnerable balances without compromising its immutability principles.
