“The danger is real,” declared the MIT Technology Review in November 2017. This “existential threat” to blockchain could be its “end,” render it “obsolete,” or prove to be its “Achilles’ heel.”

Quantum computing looms over blockchain like SEC regulations loom over crypto traders. It’s approaching, slowly but surely, and could either destroy blockchain’s promise or strengthen it. It depends on who you ask.

Up until now, most conversations about quantum computing presented it as a pure threat to blockchain. The threat’s in the numbers. While computers traditionally are made up of bits in one of two states (one or zero), quantum computers’ bits (“qubits”) can exist in a number of states that increase exponentially with the number of qubits. Sounds threatening, indeed.

Blockchain users’ digital signatures (aka their private keys), are vulnerable to quantum computers, whose calculating abilities exceed those of normal computers. While a blockchain user’s public key can be easily generated from their private key, doing the opposite takes extremely difficult calculations. Today’s computers can’t manage them, but future quantum computers could.

Blockchains’ current private key set-up “could be completely broken by a quantum computer as early as 2027,” Divesh Aggarwal of the National University of Singapore wrote in a study about quantum computers’ threats to blockchain security last year.

But what if, in addition to being blockchain security’s biggest “existential” threat, quantum computing also turned out to be its most effective safeguard?

A new article in Nature by researchers at the Russian Quantum Center in Moscow breaks down the problem “one-way” private key functions pose to blockchain and how quantum computing can solve it. The Center’s self-described goal, for the record, is to “integrate itself into the international scientific community and take on a leading positions in quantum science and technologies.” One of its authors, Alexander Lvovsky, is also a physics professor at Oxford, while the other two researchers, Aleksey Fedorov and Evgeniy Kiktenko, appear to be based in Russia. Here are the main takeaways from their exploration:

Private keys aren’t all they’re cracked up to be.

A digital signature is the “sole line of defense” for blockchain users hoping to keep their information or cryptocurrency safe, says the article. When quantum computers with the power to figure out their private keys come along, there will be—as of now—nothing else standing in the way.

Fedorov and company contrast this with banks, where clients have “plastic cards, security questions, identity checks, and human cashiers” forming a wall between their finances and everyone else. These checks are often considered to be inferior to blockchain’s security, especially because they’re in the hands of centralized banks, which have the power to lock you out of your account, or drain it, or get hacked. With quantum computing on the horizon, maybe blockchain security needs additional checks like these, the article posits.

Blockchain security’s “imminent” quantum threat is more imminent than you think.

Fully operational quantum computers aren’t expected to arrive this decade. However, Fedorov et al. note that quantum computational devices with “more limited capabilities” could crack blockchain signatures well before that. They point to in-progress quantum computing work by both D-Wave and Google.

D-Wave claims to have made a 2,000-qubit quantum computer, meaning it could run two to the 2,000th power calculations at once. That’s a very high number. Google boasts a 72-qubit processor, while IBM has a 50-qubit model.

Quantum computers will give a new meaning to immutability.

Quantum communications can’t lie, the authors point out. According to physics, you can’t copy a quantum state without changing it, a thought that could bring peace of mind even to those who doubt the security of owning a private blockchain key.

Something truly immutable (or rather with such easily traceable mutability) could replace blockchain encryption. But, like so many other promising solutions to privacy and security, it’s prohibitively expensive and complicated—at least until research has progressed.

A “quantum internet” could lead to “quantum blockchains.”

Once multiple quantum computers have been developed, they could be connected to form a network. One parallel with a blockchain network would allow for the creation of a quantum blockchain where data get processed quickly and with increased security. Such a communications network, however, is more a wish list item than a forthcoming reality. In the meantime, the Nature post provides little by way of an alternative, suggesting only that blockchain platforms up their “flexibility.” They should be “capable of changing cryptographic algorithms on the fly.”

Researchers from the Russian Quantum Center weren’t the first to propose quantum computing as an aid to blockchain security. Del Rajan and Matt Visser, from the Victoria University of Wellington in New Zealand, have discussed how quantum particle entanglement could track attempted changes to a blockchain. Quantum particles can also be entangled in time, meaning all preceding particles get encoded into the latest one.

Encoding data on a quantum particle would create the genesis quantum block, and from there, you’d be able to make—wait for it—“a quantum networked time machine,” say Rajan and Visser. Don’t ask questions. This is physics.