This week, Google published a paper explaining how a quantum computer can find a private key in bitcoin in 9 minutes, which has ramifications for Ethereum, other tokens, private banks, and everything in the world.
Quantum computing is easy to mistake for a faster version of conventional computing. But it’s not a more powerful chip or a bigger server farm. It is a very different kind of mechanism, different from the state of the atom itself.
A quantum computer starts with a very cold, very small shell of metal where particles begin to behave in ways they don’t behave under normal Earth conditions, ways that change what we think of as the basic laws of physics.
Understanding what that means, physically, is the difference between reading about quantum threat and understanding it.
How computers and quantum computers really work
Conventional computers store information as bits – each one can be either a 0 or a 1. A bit is a small switch. Physically, it is a transistor on a “chip” – a microscopic gate that allows electricity to pass (1) or not (0).
Every picture, every bitcoin transaction, every word you ever type is stored as patterns of these switches being turned on or off. There is nothing miraculous about it; it is something that appears in one of two distinct situations.
Each digit combines 0’s and 1’s very quickly. A modern chip can do billions of these per second, but it still does them one at a time, in sequence.
Quantum computers use what are known as qubits instead of bits. A qubit can be 0, 1, or – and this is the amazing part – both at the same time!
This is possible since a qubit is a completely different type of physical object. The most common type, and the one that Google uses, is a small layer of large metal cooled to about 0.015 degrees above zero, colder than outer space but here on Earth.
At that temperature, electricity flows through the loop without any resistance, and is now said to exist in a quantum state.
In a superconducting loop, current can flow clockwise (counting 0) or counterclockwise (counting 1). But in quantum measurements, the current does not have to choose one direction and actually flows in both directions at the same time.
Don’t make the mistake of switching between the two too quickly. It is now in a quantitative, experimental and validation process in both provinces at the same time.
The physics of mind
And us so far? It’s great, because that’s where it’s really amazing, because the physics behind how it works isn’t immediately obvious, and it shouldn’t be.
Everything that man interacts with in everyday life obeys classical physics, which assumes that things are in the same place at the same time. But particles do not behave this way at the subatomic level.
An electron has no definite position until you look at it. A photon has no apparent polarization until you measure it. The charge in the superconducting loop does not flow in a clear direction until you force it to select.
The reason why we don’t see this in our daily life is the lack of unity. When a quantum system interacts with its environment, molecules of air, heat, motion and light, the superposition collapses almost instantaneously.
A soccer ball cannot be in two places at once because it interacts with billions of molecules of air, dust, sound, heat, gravity, etc., every nanosecond. But isolate a tiny current in a near-zero vacuum, shield it from every possible disturbance, and quantum behavior lives long enough.
This is why quantum computers are so difficult to create. Humans are an engineered environment where the laws of physics that normally prevent these things from happening don’t apply long enough to do the math.
Google machines operate in refrigerators the size of large rooms, colder than anything in the natural universe, surrounded by protection against electrical noise, vibration and heat radiation.
And qubits are fragile however. They lose their quantum state over and over again, which is why “error correction” dominates every conversation about scaling.
So a quantum computer is not a faster version of a classical computer. It exploits various laws of nature that only work in very small conditions, very low temperatures and very short periods of time.
Now collect that.
The two normal bits can be in one of four states (00, 01, 10, 11), but only one at a time (since current only flows in one direction). Two qubits can represent four states at the same time, since the current flows in all directions at the same time.
The three qubits represent eight states. Ten qubits represent 1,024. Fifty qubits represent more than a quadrillion. The number doubles with each qubit added, which is why the rate is so powerful.
The second trick is something called entanglement. When two qubits are entangled, measuring one immediately tells the observer something about the other, no matter how far apart they are. This allows a quantum computer to connect across those states simultaneously in a way that a parallel computer cannot.
And these quantum computers are programmed so that negative responses cancel out (like cold currents) and positive responses reinforce each other (like high currents). At the end of the calculation, the correct answer has a high probability of being measured.
So it’s not a brute-force race. It’s a very different form of math – one that allows nature to explore a vast space of possibilities and arrive at the correct answer through physics rather than logic.
A major threat to cryptography
This mind-boggling physics is why it’s so scary for encryption.
Mathematical security in bitcoin is based on the assumption that checking each key can take longer than the age of the universe.
But a quantum computer doesn’t check every key. It checks them all at once and uses an interrupt to produce the correct one.
That’s where it connects to Bitcoin. One way, from private key to public key, takes milliseconds. On the other hand, going from a public key back to a private key would take an ancient computer a million years, or longer than the age of the universe. That asymmetry is the only thing that proves that someone is holding their coins.
A quantum computer using an algorithm called Shor’s can enter the trapdoor from behind. A Google paper this week showed that it can do so with far fewer resources than anyone previously estimated, and for a time it competes with bitcoin block seals.
That’s why the threat of quantum computers breaking the blockchain’s encryption really worries everyone.
How the attack works step by step, how Google’s paper has been specifically modified, and what it means for the 6.9 million bitcoins that have already been exposed, is the subject of the next piece in this series.
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