Bitcoin miners use their computing powers to solve cryptographic puzzles which, te turn, build up the blockchain by adding blocks of transactions. This process is fundamental to how Bitcoin transactions are authorised te the absence of a central authority, albeit the energy consumption involved has raised concerns.

Now a fresh threat to the blockchain is on the horizon. Quantum computers, could, with their terrific computing power, crack the public key encryption that determines the relationship inbetween a public and private key.

### Background to Quantum Computing

Ter a classical laptop all data—text, pics, even audio—is stored spil sequences of *binary* numbers. Te a binary system every chunk of gegevens stored or processed can only take two values “1” or “0.” Early laptop pioneers used this binary system because it wasgoed the only practical solution given hardware based around plain on/off switches ( *transistors* ).

Modern computers may seem exceptionally ingewikkeld, but they’re built from many millions of thesis ordinary on/off building blocks.

Key, tho’, is that each speck of data—each **bit** —is undoubtedly either a zero or a one. No other states exist. And your laptop is deterministic: if you ask it to perform a calculation on a particular sequence of gegevens repeatedly, it’ll give you exactly the same result every single time.

Quantum computers, however, differ radically. Instead of working with classical onaardig, which are undoubtedly either a one or a zero, quantum computers use quantum snauwerig: **qubits** . Qubits are somewhat mind-bending te that they can be te an unknown, undetermined state: they can represent a one and a zero at the same time, only actually determining on what state they truly were, after you’ve performed calculations on them.

### Solving the puzzles

The crypto puzzle concept at the core of blockchain technologies is elementary to explain, but time-consuming to solve: it takes the form of “I have a complicated equation, and a known result – but what number would I have to have input into the equation to get that result?”

The only way classical computers can solve such a problem (and hence crack the security of crypto) is by using brute force, attempting every possible input to the equation until the result comes out right. The equation has to be calculated every single time until you klapper success, which is impossibly time-consuming.

Broadly speaking, quantum computers work the other way around: they can test all the possible inputs at the same time: you pick the result you wished, and only then do the qubits—the inputs—reveal what state they needed to be te for that result to toebijten.

So quantum computers make it possible to search for needles ter haystacks amazingly prompt. Which makes them flawless for dealing with big numbers.

### Big numbers

Each Bitcoin private key is a randomly generated number 256 kattig long. This gives 2^256 (Two to the power of 256) possible keys, or

1,597,920,937,330,902,918,203,684,832,716,283,019,655,932,542,976 possible keys.

To waterput that ter perspective, there are only an estimated 2^63 grains of sand on all the beaches on Earth. If each grain of sand wasgoed itself a little planet containing all the grains of sand on earth, there would still be more possible Bitcoin addresses than grains of sand by a gigantic number.

Brute force guessing an address using an average 2018 pc is therefore impractical, it would take astronomically longer than the age of the universe. Even using all the computing power on earth wouldn’t commence to touch the problem.

### So what’s the problem?

Theoretically, with enough power, a quantum rekentuig would be able to speed up this brute force process radically. Let’s take a look at where the threat is, and how it can be mitigated:

Both of thesis converts are essentially one-way, unbreakable with current pc technology. To work rearwards from them would require a brute-force treatment which, spil wij’ve seen, is simply not practical with current computers.

Unlike binary computers however, quantum computers are potentially capable of working rapid enough to pauze the very first of thesis – the public/private key elliptic curve function – ter a reasonable timeframe.

Researchers from Cornell are predicting that spil a worse-case screenplay, quantum computing could crack the elliptic curve function ter about Ten minutes by 2027 [1] .

However, hackers need to get to the public key to do so. Spil long spil an address hasn’t bot used more than once, quantum computers cannot similarly switch sides the 2nd HASH160 algorithm used to generate the addresses.

So, te brief, spil things stand, Bitcoin funds are safe from potential quantum computing threats spil long spil:

- they are stored te an address that you have not sent money from (so the public key is unknown) and,
- You only use each receiving address generated from that public address once.

So all is not lost, even if quantum computing materialises spil a serious threat. Albeit wij may have a period where wij need to be very careful while Bitcoin’s algorithms are updated to mitigate this threat.

### How real is the threat?

The 2027 prediction above, spil with all predictions concerning Bitcoin, should be treated with some scepticism. For a embark, no one is fairly sure when, if everzwijn, thesis computers will be produced with enough qubits to crack the public key encryption that protects Bitcoin users.

A researcher at Hebrew University ter Jerusalem, Schreeuw Kalai, has stated quantum computers cannot work, even ter principle. Kalai believes that, “noise [random and unavoidable errors] will omkoopbaar the computation.”

However, it shows up the opponents of quantum computers are a minority. Large corporations such spil IBM, Facebook and Google spil well spil governments and inter-governmental organisations such spil the European Union are spending billions of dollars researching this field.

Recently Google unveiled its fresh quantum computing chip called the “Bristlecone” which contains a record 72 qubits. This is a significant increase from the 50 qubits achieved by IBM last year.

Putting this into perspective however, some pundits are telling that to get the ‘safe cracking’ down to under an hour a quantum machine would need to have around half a million qubits, it’s clear wij have a way to go before it’s a real threat.

Meantime the cost of such machines means they are, for the ogenblik at least, only available to large tech companies and governments, and large teams of physicists and engineers are needed to ensure the cooling system and energy consumption remain under control.

Will wij see a quantum omschrijving of Moore’s law? Gordon Moore (the founder of Intel) made the uncannily accurate prediction ter 1965 that the number of transistors on an integrated circuit would harshly dual every two years. This exponential growth rate has proven beautifully accurate, and has bot accompanied by the exponential growth te power of conventional computers. A similar rate of growth would see us go from the current 72 to half a million qubits te around 26 years.

### Possible Solutions

If it is to be assumed that quantum computing will exist te the future then the cryptography upon which Bitcoin and other blockchains rely, will eventually have to adapt.

One possible way te which this could be done is through the use of ‘Lamport signatures’, a variant on public-private key cryptography thought to be quantum-hardened. Another treatment may be the nascent field of quantum cryptography. Research into other encryption systems is still ongoing with a concentrate on ensuring it is safe from a brute force quantum attack whilst, at the same time, not undermining the principles outlined by Satoshi Nakamoto te the Bitcoin white paper.

The CoinDesk article, The Fresh Ways to save Crypto from Quantam written by Alyssa Hertig discusses other possible solutions.

Many financial institutions, such spil banks and stock exchanges, use the same or similar encryption to protect their gegevens. If quantum computers are to be a threat to Bitcoin then they will also be a threat to all other institutions and programs that rely on classical cryptography.

It is arguably lighter for a centralised institution to adapt and strengthen its encryption than a decentralised network like Bitcoin. The rows overheen Segwit and other innovations are demonstrative of the immense difficulty with the tempo at which Bitcoin can switch even when switch is necessary.

The general reaction from the crypto community to the threat of quantum computing has bot one of indifference so far, perhaps because the machines are so far from being a threat at the uur. But knowing how prompt the field of computing can switch, and how quickly exponential growth can creep up on us, this is an area that clearly bears keeping an eye on.