The Quantum Issue: WTF Is Quantum Computing?

What is quantum computing? How is a quantum computer different from a regular computer? What relevance does this have to Bitcoin?

New Bitcoiners have been inevitably bumping into these questions and having to confront the issues they dredge up regarding Bitcoin’s exposure to what is very much an existential threat to its existence if a viable quantum computer were to be developed. 

The ability to own bitcoin rests on the foundational assumption that without directly leaking a copy of it, no one but the person who possesses a private key can sign to transact with coins secured by that key. Quantum computing calls that assumption into question. 

Quantum computers are not just “computers, but faster.” They function in a very fundamentally different way from a classical computer, and as such they are much more efficient than classical computers at very specific kinds of computations. Now obviously, I’m not going to actually explain how quantum computers work in minute detail within four pages, but I will give you the core intuition of how they are fundamentally different from a classical computer. 

So let’s take a look at how both kinds of computers interact with things like large cryptographic keys.