Last Wednesday, Google’s quantum researcher Craig Gidney published the results of a study according to which breaking Bitcoin would be much easier than expected.
In particular, according to Gidney’s study, decrypting RSA encryption would be 20 times easier than previously thought.
The study by the Google researcher: quantum computers can break Bitcoin
Gidney writes that to plan the transition to quantum computer-resistant cryptographic systems, one must first understand the cost of quantum attacks on vulnerable cryptographic systems.
He cites a previous study of his from 2019 in which he estimated that to break entire 2048-bit RSA, it might take just eight hours of work by a quantum computer with 20 million qubits.
In the recent study, however, it reduced this estimate to less than a week, and with a quantum computer with less than 1 million qubits.
Gidney also explains how it was possible to imagine reducing the estimates so much thanks to new calculation and storage techniques.
Quantum Computers Against Bitcoin
Currently, quantum computers barely manage to surpass 1,000 qubits, but until a few years ago they didn’t even exist.
In fact, although the idea of quantum computers had already emerged in the 1980s of the last century, the first quantum computer was built just a little over twenty years ago, and it had only 12 qubits.
Furthermore, the so-called “quantum supremacy” was only achieved in 2019 by Google with a 53-qubit processor. Quantum supremacy refers to the ability of a quantum computer to perform a specific computational task in an enormously shorter time compared to that taken by the most powerful classical supercomputer existing to solve the same problem.
IBM, for example, has the ambitious goal of reaching 10,000 qubits by 2029, and of creating a quantum supercomputer with 100,000 qubits by 2033.
At this rate, it will take well over a decade to reach one million qubits. Moreover, such power will only be available to a few supercomputers, so for now there is no risk that Bitcoin could be compromised.
Quantum Computers and Bitcoin
The point is that quantum computers have a computing power enormously superior to that of traditional computers.
Therefore, some cryptographic methods that were too difficult to decrypt with classical computers could instead be decrypted by enormously more powerful quantum computers.
In this case, it is the RSA (Rivest–Shamir–Adleman) asymmetric encryption algorithm invented in 1977 by Ronald Rivest, Adi Shamir, and Leonard Adleman.
RSA makes decryption very difficult because it requires factoring a very large number into two prime numbers that are also very large. Since this process is practically impossible for classical computers in reasonable time, it is practically impossible to derive the private key from the public one, and for this reason, the RSA algorithm is currently considered very secure.
Asymmetric cryptography RSA is the foundation of Bitcoin, because it is with this system that the pairs of public and private keys are created on which transactions in BTC are based. The public key is used to verify the correctness of the digital signature of the transactions, while the private one is used to sign. Without the private key, you cannot sign the transactions of your wallet, and from the public key, there is no way to trace back to the private one.
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The solutions
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Initially, after the 2019 study, it was thought that it would take at least twenty years before quantum computers would be able to put Bitcoin at risk.
Now, however, that estimate will probably be revised downwards.
However, this does not mean that Bitcoin is doomed in the short term.
In fact, although the Bitcoin protocol cannot be modified, it is always possible to fork it, that is, to create another modified version to accompany the classic one.
The idea is to create a fork resistant to quantum computers, and to start using that instead of the original protocol, also because the latter could eventually be compromised.
Moreover, it has been years since the problem became known, and by now possible solutions have already been developed to adopt on the fork in order to make it quantum resistant.
However, if until recently it was thought that there was plenty of time to intervene, now it seems likely that it is necessary to act more quickly.
It should be remembered that to perform a fork of Bitcoin that can then be adopted by all (or almost all) users takes time, and what Gidney tells us is that we have less of it than we thought.