Quantum computers are coming and encryption – including the kind used to underpin cryptocurrencies – is in trouble, researchers say.

That's according to researchers at the National University of Singapore and colleagues who have estimated how soon the computers might be able to break bitcoin's security. Based on the most aggressive estimates for the advancement of quantum computation, private keys might be cracked as early as 2027, their paper says.

Bitcoin encryption today is ensured by the difficulty of cracking its code using existing computers, but quantum computers will theoretically be able to work much faster because they are not constrained to working with bits (values that are either 0 or 1). Quantum computers use qubits, which take advantage of the very strange ways subatomic particles behave to contain more values (or even two values at once).

As first reported by the MIT Technology Review, the researchers investigated quantum computers' application against both mining pools and using the machines to attacks private keys. Miners will be safe for longer than wallets, the researchers contend.

The greatest danger for bitcoin users will come when transactions have been broadcast to the network but not yet processed, according to the paper.

An attacker with a quantum computer is likely to be able to change the transaction before the legitimate one goes through, the researchers found.

Settled transactions will remain safe, at least for a while. Even a paradigm-shifting computer is unlikely to be able to change the ledger after several blocks have been processed.

If private keys are compromised, that's not just bad news for cryptocurrency. It would expose anything else that uses public-private key encryption, such as messaging apps, SSL certificates and data storage.

As the researchers acknowledge, this finding holds true provided nothing changes in the way private keys are created. They write:

However, their discussion neither completely endorses nor dismisses any of the proposals.

This summer, researchers at the University of Pennsylvania also proposed ways in which more robust private keys could stymie these new machines. And, as has been argued, quantum computers might also develop much more slowly than the researchers have modeled.

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