Bitcoin industry players and researchers are speeding up efforts to prepare for the possibility that its security could one day be broken by quantum computers. So-called Q-Day has not materialised. Still, multiple layers of defences are being reviewed at the same time, from quantum-resistant transactions to bitcoin protocol upgrades and stronger custody systems at exchanges.

Blockchain outlet Decrypt reported on Saturday that moves in the bitcoin industry to respond to the quantum computer threat are advancing along three tracks: transactions, protocol and custody.

Q-Day refers to the point when sufficiently powerful quantum computers emerge and can break today’s cryptographic systems. Bitcoin uses elliptic-curve cryptography to sign transactions by linking private and public keys. If quantum computers advance enough to run Shor’s algorithm, concerns have been raised that they could compute private keys from public keys and forge signatures.

No quantum computer at that level exists at present. Q-Day is also still a hypothetical scenario. Even so, as forecasts about the pace of quantum computing development shift, calls are growing in the industry to prepare countermeasures in advance.

One of the fastest-moving approaches is to implement quantum-resistant transactions while keeping existing bitcoin rules. StarkWare said last month it mined the first quantum-safe bitcoin transaction on mainnet. It also said a public competition lowered the estimated cost needed to build such a transaction to about $67 from about $320.

That approach alone cannot protect bitcoin as a whole from quantum threats. StarkWare also explained that the transaction is non-standard and applies only to coins whose public keys have not yet been exposed. Over the long term, it sees a soft fork that changes the bitcoin protocol itself as a more fundamental solution.

The second measure is to introduce quantum-resistant signatures into the bitcoin network itself. Applying cryptography that is strong against quantum attacks instead of existing elliptic-curve-based signatures could build a long-term defence system.

The challenge is bitcoin’s decentralised governance structure. Introducing a new signature scheme requires design, validation and testing to secure community consensus. A deployment process would still be needed after that, which could take significant time. The fact that full-scale discussion of quantum threats is relatively recent is also cited as a burden.

The third track is how exchanges and custodians protect assets they hold. Coinbase's head of cryptography said it is preparing a post-quantum custody system at the exchange level to protect about $250 billion in assets.

Coinbase is preparing a custody structure that can respond regardless of what signature scheme bitcoin adopts in the future. It has also been reported to be reviewing hardware-based alternatives in case a new quantum-resistant signature scheme is not compatible with the key-splitting techniques used by existing custodians.

Quantum-threat responses are also being linked to discussions about strengthening bitcoin privacy. That is because some quantum-resistant cryptographic technologies could tie in with techniques that protect transaction information. Researchers also recently disclosed a design for bitcoin transfers that uses a shielded method similar to Zcash.

The countermeasures proposed so far each have limitations. Quantum-resistant transactions have a limited scope of application, and protocol upgrades need time for consensus and development. Custody systems are also focused on protecting assets held by exchanges and institutions, and do not solve problems for the bitcoin network as a whole.

Ultimately, what the industry is watching is the gap between the pace of quantum computer development and the pace of preparedness of defensive technologies. Even if Q-Day has not yet materialised, it could be too late to respond after a real threat emerges.

These moves show that bitcoin’s response to quantum computers is expanding beyond a research topic to actual transactions, custody systems and protocol design. How quickly quantum-resistant technologies are commercialised, how quickly the bitcoin community reaches consensus, and how fast quantum computer performance advances are expected to shape bitcoin’s level of long-term security preparedness.