Quantum Computers a Threat to Bitcoin Security

https://www.technologyreview.com/s/609408/quantum-computers-pose-imminent-threat-to-bitcoin-security/

A crucial feature of Bitcoin is its security. Bitcoins have two important security features that prevent them from being stolen or copied. Both are based on cryptographic protocols that are hard to crack. In other words, they exploit mathematical functions, like factorization, that are easy in one direction but hard in the other—at least for an ordinary classical computer.
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So Aggarwal and co specifically examine the likelihood of a quantum computer becoming that powerful on the network. They look at the projected clock speeds of quantum computers in the next 10 years and compare that to the likely power of conventional hardware.
Their conclusion will be a relief to Bitcoin miners the world over. Aggarwal and co say that most mining is done by application-specific integrated circuits (ASICs) made by companies such as Nvidia. This hardware is likely to maintain a speed advantage over quantum computers over the next 10 years or so.

“We find that the proof-of-work used by Bitcoin is relatively resistant to substantial speedup by quantum computers in the next 10 years, mainly because specialized ASIC miners are extremely fast compared to the estimated clock speed of near-term quantum computers,” they say.
But there is a different threat that is much more worrying. Bitcoin has another cryptographic security feature to ensure that only the owner of a Bitcoin can spend it. This is based on the same mathematics used for public-key encryption schemes.

The idea is that the owner generates two numbers—a private key that is secret and a public key that is published. The public key can be easily generated from the private key, but not vice versa. A signature can be used to verify that the owner holds the private key, without revealing the private key, using a technique known as an elliptic curve signature scheme.
In this way, the receiver can verify that the owner possesses the private key and therefore has the right to spend the Bitcoin.

The only way to cheat this system is to calculate the private key using the public key, which is extremely hard with conventional computers. But with a quantum computer, it is easy.
And that’s how quantum computers pose a significant risk to Bitcoin. “The elliptic curve signature scheme used by Bitcoin is much more at risk, and could be completely broken by a quantum computer as early as 2027,” say Aggarwal and co.
Indeed, quantum computers pose a similar risk to all encryption schemes that use a similar technology, which includes many common forms of encryption.
There are public-key schemes that are resistant to attack by quantum computers. So it is conceivable that the Bitcoin protocols could be revised to make the system safer. But there are no plans to do that now.