# The Blockchain: Quantum Attacks and Quark Attacks (Explain Like I’m 5)

…continued from: Tales from the Crypto: Double Spending and the 51% (Explain Like I’m 5)

Hi Cryptoman. A friend emailed me saying “Sell all your Bitcoin, quantum computers will destroy the blockchain.”

#### What are quantum computers? And will they destroy the glorious blockchain?

You know the computers you’re familiar with, made from chips that have transistors-based logic circuits burned into them. You know that they represent data using various binary codes?

#### Maybe.

I’ll pretend you do, although you clearly don’t.

So, in 1980, two guys called Benioff and Manin dreamed up the idea of a quantum computer. It was very different design for a computer than the ones we’re familiar with. The computers we’re familiar with were dreamed up by Alan Turing in the1930s before World War II. It’s a very old idea.

#### Alan Turing? Who he?

He was a Brit who invented a mathematical model of a computer, called the Universal Turing Machine. It proved to be a practical model too. So, all modern computers are, at their foundation, Universal Turing Machines.

I won’t try to explain the math, because I don’t want your head to explode. It would make a terrible mess of the wallpaper.

So, to cut a complex story way too short, there is also a Quantum Turing Machine, an abstract mathematical model of the possibilities of a quantum computer. This Quantum Turing Machine demonstrates mathematically that a quantum computer can do anything a normal computer can do.

#### I have no idea what you’re talking about. Are you telling me people can make computers out of quantums?

It’s not quantums, it’s quanta, you dingbat.

I suspect, with a pinch of certainty, that you don’t know anything about Quantum Mechanics.

#### It’s true. I misspent my youth elsewhere.

So you are not going to get this, but anyway…

Physicists use Quantum Mechanics to model the way things happen on a subatomic scale. It’s the only theory that explains the results of various landmark experiments. It’s mathematical. For example, there’s a probabilistic wave function that estimates various physical properties of a subatomic particle. And it works.

#### Are you trying to bore me to death?

Yes, but it’s not working. So, I’ll cut to the chase.

Using quantum physics, you can build a computer that works with quantum bits rather than bits. These quantum bits are called “qubits.”

#### So what?

With quantum computers, instead of having a bit that can only have the value 0 or 1, you have qubits which have a “superposition” of 0 and 1. What that means, in practice, is that a qubit can take all the values in the range 0 and 1 — at the same time.

#### My head hurts.

That was always going to happen, RookieBoy. Take a couple of aspirin, and I’ll keep talking.

This “superposition” thing makes it possible to build a computer that works in a massively parallel way.

#### Meaning what?

Think of thousands of computers collaborating to produce an answer fast by sharing the work. Now think of a single computer that can behave as if it were thousands of computers. It would be very fast — faster even than Usain Bolt.

So if you want to ignore everything I’ve said so far, you can settle for: quantum computers are much faster.

#### Great, When will I be able to get one from Best Buy?

Not any time soon. At the moment they are a little pricey.

#### How much?

Think $10 million. You could pay that much for a quantum computer from D-Wave. But it might be worth it. For some select problems, it runs 100 million times faster than the designer-desktop you bought at the Apple store.

#### So how long will it be before the quantum computer breaks Bitcoin and casts it thoughtlessly into the dustbin of technology history, along with my little stash of crypto?

No-one knows for sure. One expert, Google’s quantum computing aficionado, John Martinis, thinks it may take another decade. He says that qubits are unstable and physicists have yet to find ways to keep them stable enough to attack general computing problems like encryption. He should know, Google gave him a quantum computer to play with.

#### So they can’t break encryption yet?

No. But when there’s a quantum computer powerful enough, it will be able to break most encryption. In particular, it will be able to break the public key cryptographic scheme that currently keeps a good deal of encrypted data safe.

This is known to be true.

A smart mathematician called Peter Shor wrote a quantum algorithm that can find the prime factors of any integer. If you can do that fast, you can break public key encryption — and that means you can also hack the digital signatures used by cryptocurrencies — and that means your stash of crypto will be vulnerable.

#### So how can cryptocurrencies defend themselves?

There’s a field of cryptography called post-quantum cryptography or quantum-safe cryptography where mathematicians dream up algorithms that can defeat a quantum computer. The math guys already have such algorithms. Cryptocurrencies could employ such algorithms

#### So, is this quantum computer thing just a storm in a teacup?

For cryptocurrencies, it probably is, because cryptocurrencies could switch out their algorithm for one that works. The real problem is that public key cryptography has been used everywhere for years. When quantum computers get powerful enough, there are bound to be situations that bad guys armed with a quantum computer can exploit.

I see the quantum computer as more of a threat to legacy computing than crypto.

#### What do you mean by legacy computing?

Old stuff that should have been replaced long ago.

#### So what can you tell me about Quark Computers?

They are like hen’s teeth; they don’t exist.

#### But I can Google “Quark Computers,” and I get results.

That’s just physicists and engineers speculating. They don’t exist.

#### When I Google “hen’s teeth” it takes me to a web page which refers to a species of chicken called Taipid that has a complete set of teeth.

Damn you, Google.

Click here for: Proof of Stake? Does That Have Anything To Do With Dracula Coin? (Explain Like I’m 5)

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