The issue of quantum computing has been gaining more and more interest within the crypto sphere, particularly in the last 12 months. Given the growing curiosity and concern, it is worth solving some open questions about quantum supremacy for the crypto community, as there is a tremendous amount of misinformation circulating online.
Will our Bitcoins be stolen?
Many people harbor the fear that Sycamore, Google’s 54-qubit quantum processor, may be smarter than the system and steal everyone’s Bitcoin. If there were no changes in the current implementation of the Bitcoin network, this would most likely become a reality within five or ten years. So, although there is currently no need for users to worry, developers are advised to start preparations.
What is truly alarming is that the “quantum deniers” refute the reality of the problem and insist that worry must be stopped. Unfortunately, what happens is the exact opposite. We must put a collective approach to solving the problem, since complex distributed systems (does the Blockchain sound to you?) Are anything but easy to upgrade to a completely new cryptography stack. Having spent a decade or two maturing, the ecosystem could be massively undermined if quantum computing advances to the expected degree.
The certainty about this comes from the fact that current encryption schemes (including those used by Bitcoin and Ethereum) have already proven vulnerable to counterfeit signatures executable by quantum computers.
Asymmetric cryptography is based on key pairs (that is, a public key and a private one), where the public one could be calculated from its private counterpart but not vice versa. This is due to the impossibility of certain mathematical problems such as the factorization of a number that is the product of large cousins or the calculation of the generator multiplication that gave rise to a public key, which most Blockchains and cryptographic systems use.
If the calculation could be done backwards (that is, by calculating a private key from a public key), the whole scheme would be broken. All we need is more qubits and stability in these systems so that such attacks become executable.
Will Google extract all the rest of Bitcoin?
This is another question that is often asked, but in reality, quantum computers are much less efficient in calculations related to symmetric cryptogram than in those related to asymmetric cryptogram. As for the numbers, 2^128 operations on a conventional computer are needed to locate a Bitcoin private key from a given Bitcoin public key, while only 128^3 operations on a quantum computer are needed to achieve the same feat.
In the case of hashing, the difference – although still huge – is much smaller. In essence, we need to worry more about people with quantum computers spending/stealing our money instead of worrying about Google extracting the remaining Bitcoin. Even if that were the case, after successfully removing 2016 blocks, it would put the difficulty at “quantum level” – which means that Bitcoin would only be removable by quantum computers.
The difficult question here is that the difficulty is reaching such levels that the miners need to wait to be able to readjust the time field of the given blocks because they have already gone through all possible nuance for a given block without finding a result below the objective of difficulty. In light of this, I would say that this problem related to mining is more theoretical than practical. We have already noted that time may be the limiting factor in finding a correct solution for a block, not performance, even without mining based on quantum computing.
The only thing everyone should focus on
Should Bitcoin holders worry about the quantum problem in 2020? No, but there is a caveat: cryptocurrencies (that is, their developer communities) and companies should focus on the issue.
What if there are already built quantum computers that are much more capable than Google Sycamore and we are not allowed to know them?
We should look for and upgrade to a cryptographic stack resistant to quantum computing in Blockchain implementations and all other systems that rely on asymmetric cryptogram (for example, banks, governments, etc.) as soon as possible. Quantum supremacy is inevitable – it’s just a matter of asking ourselves when.