What would be the use of a data transmission system where the contents of a message changed if anyone simply read it?
Imagine if our two dearest cryptocurrency enthusiasts, Alice and Bob, could exchange secret keys through such a medium?
In this case, if anyone were to try and eavesdrop on their communications, the exchanged keys would arrive at their destination with a tell-tale mark that they had been seen by their enemy, infamous spy Eve.
This technology has been out there since at least 1984, and it's called Quantum Key Distribution, or QKD for short.
QKD uses properties from, you guessed it, Quantum Physics.
It leverages one of the most famous physical principles in modern science: the Heisenberg Uncertainty Principle.
Werner Heisenberg proved that it is impossible to know all the information available about atomic particles at the same time.
For example, if you knew the exact position of a photon, for instance, then you could not know its exact velocity. To know one with 100% precision, you'd have to accommodate some uncertainty in the other.
Heisenberg's Uncertainty Principle is leveraged in QKD for security purposes, specifically for secret key exchange.
Using QKD, a sender is able to transmit some particle (usually a photon) that is polarized in a particular way.
If anyone were to try and "inspect" this payload along the way, the particle would change state and, given some redundancy test (or error correction algorithm), the receiver would be able to know that someone had intercepted the transmission somehow.
How does this incredible concept fit into the cryptocurrency universe?
There are many possible ideas for interesting uses of QKD in cryptos, but none of them have been considered for implementation yet.
Quantum computing is, after all, still a few decades away from mass adoption.
Here are a few ideas for QKD in the cryptocurrency space:
Quantum computing in general is a promising field for cryptography and, of course, cryptocurrency researchers.
Academics have warned that Bitcoin might be vulnerable to quantum computing attacks and, as such, the most popular crypto will require upgrades in order to stay secure in the coming decades.
Quoting a piece from The Register:
As far as defeating hashcash goes, the numbers are daunting for quantum computer designers: by 2028, the researchers reckon, you'd need a 4.4 million qubit machine to achieve 13.8 gigahashes per second: “This is more than one thousand times slower than off the shelf ASIC devices which achieve hash rates of 14TH/s”.
Several key distribution protocols are already available for QKD and many more will likely appear in the coming years, especially as cryptocurrency research gains further ground in academia.
In October 2019, Google announced that they had achieved quantum supremacy.
This unprecedented achievement marks a significant step towards widespread adoption of quantum computers.
Achieving quantum supremacy means that a quantum computer went beyond what a traditional binary computer can do.
The way this is tested is two computers receive increasingly difficult programming tasks. One is a quantum computer, the other is a traditional computer. When the quantum computer quickly solves a problem that causes the other computer to halt or take forever to solve, then we say we have achieved quantum supremacy.
In Google's experiment, the quantum computer took 200 seconds to solve a problem the traditional computer would take an estimated 10 thousand years to complete.
But you need not worry in the short term. Despite the impressive results, quantum computers are still a long way from threatening Bitcoin.
Google's Sycamore quantum processor has 54 qubits. It is estimated that at least 1500 qubits would be necessary for a realistic attack against Bitcoin. This is still many years away from current state of the art quantum hardware.