Government intervention, poor usability, high network fees – which one of these poses the most significant threat to Bitcoin? The answer may be none of them.

Although the Bitcoin network is incredibly secure under the current condition of computers, there’s an even greater threat looming overhead. Quantum computers could render Bitcoin’s security systems obsolete and decimate the once-dominant cryptocurrency.

What is Quantum Computing?

Simply put, a quantum computer is a supercomputer held at near absolute zero temperatures (-459.67degF). The subatomic particles of the processor in the computer act in ways that aren’t possible under normal conditions at this temperature.

Contrary to popular belief, quantum computers aren’t necessarily faster than traditional ones. Unfortunately, quantum computers won’t speed up your Netflix stream.

But the quantum anomalies that occur at freezing temperatures do enable them to perform calculations that are theoretically impossible for ordinary computers to execute in an acceptable time frame. These calculations can be used to simulate molecules, protein folding, or logistics optimization.

But how does a quantum computer do this?

Superpositioning and Entanglement

Quantum computers possess two properties that allow them to do complex calculations efficiently. The first is superpositioning.

Traditional computers store information as a series of 0’s and 1’s. Quantum computers, on the other hand, store their data using a set of qubits – superpositions of 0 and 1. Qubits can exist in two states simultaneously.

When you connect these qubits together in a system the number of states increases exponentially. One qubit can have two states, while two qubits can have four, four, eight, and so forth. The equation directly determines the number of states:

# of states = 2ⁿ where “n” is the number of qubits.

The second property of quantum computers is entanglement. Two qubits can be entangled together and the result is that the value of one qubit will also be measured. All superpositioned qubits in a quantum computer can be entangled to give you all possible states.

How Does Quantum Computing Affect Bitcoin?

Quantum computers excel at cryptographic calculations. This is a serious threat to Bitcoin and other cryptocurrency. We need to first understand how Bitcoin connects the public keys and private keys.

A Quick Bitcoin Refresher

Every Bitcoin wallet has both a private and public key. Your public key is your wallet address, which you use to receive funds. It’s generated from your private key. Your private key is the password you use to send funds.

To send money, especially bitcoins, you must sign every transaction with an elliptic curve signing scheme. This scheme proves to others that you own the private key without having to broadcast what it is. This scheme makes it easy to create a public key using a private one, while reverse engineering is almost impossible.

That may change soon, though, with quantum computers.

Quantum Calculations

A common misconception: One quantum computer could provide enough hashing power to perform a 51% attack on the Bitcoin network.

The reality: ASIC miners are, and will be for at least ten years, much more efficient at mining than quantum computers. There’s little to no risk of a quantum computer sabotaging the Bitcoin network through a 51% attack. Quantum computers’ ability to degrade the network’s private keys is the real threat.

The inefficiencies of modern computers keep private keys that elliptic-curve signatures generate relatively secure. It would be a waste of time and resources to try brute force to guess private keys.

A traditional computer would need to perform 2^128 or 340,282,366,920,938,463,463,374,607,431,768,211,456 basic operations to derive a Bitcoin private key from a public address.

However, using Shor’s algorithm, a significantly large quantum computer needs just 128^3 or 2,097,152 operations to figure out a private key. This is a significant reduction in the number of key relationships, which makes it possible to figure out a private key.

How Screwed is Bitcoin?

The good news: Bitcoin should be fine. It is still years away that quantum computers are capable of calculating Bitcoin’s key relationships. Solutions aren’t always as simple as they seem.

One-time Addresses

The simplest but not practical solution is to use each Bitcoin address only once. Your public address will only be visible from the moment you initiate a transaction until it enters a block. However, people rarely change their addresses with every transaction.

Signature Algorithm Change

The recommended solution is to change Bitcoin’s public key algorithm from elliptic curve signatures to an algorithm that’s quantum resistant.

Lamport signatures are a common suggestion for the replacement. These signatures are much larger than their elliptic curve counterparts, though (about 169 times larger). This size difference hinders scalability, even with the implementation of the Lightning Network.

Additionally, Lamport signature keys still have a limited amount of use before you’d need to create a new key pair. You may only need to use one of these keys.

With any modification to the public key algorithm you would also have to soft fork Bitcoin. All users should then transfer their funds to this new address type. Any funds that are left behind could be stolen.

New Cryptocurrency

Some teams have quantum resistance in mind when they build their cryptocurrency.

IOTA, for example, uses one-time Winternitz signatures to create key pairs. This strategy makes addresses inaccessible almost immediately after funds are sent. It leaves your address vulnerable to quantum attack for only a few seconds.

The Nexus team advertises their 3D-blockchain as the “first truly quantum-resistant blockchain.” It updates and obscures your keys after every transaction with a scheme the team calls “signature chains.”

Another project, Hcash applies BLISS signatures to prevent quantum computing.

The Future of Quantum Computing & Resistance

These projects are not the only ones fighting against quantum computing. Although you may not hear much about quantum resistance as it relates to other projects, they are still working on it. Ethereum, for one, has proposals that would enable different types of signature algorithms for each user.

With high-powered quantum computers still many years away, most projects will have ample time to strengthen their defenses. You can rest assured that Bitcoin will be around for the long haul.