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How Quantum Computers Could Affect Bitcoin

June 24

Quantum computer will kill bitcoin

Do you know what could stop Bitcoin in its tracks?

High fees, scalability and usability issues, even the government intervention wouldn’t hurt Bitcoin so much.

The Bitcoin network is extremely secure and no computer today could actually hack the network. But there is one computer that could pose threat to the integrity of Bitcoin and it’s called the Quantum Computer.


Before we talk about the influence of Quantum Computers on Bitcoin, we should take a look at what is Quantum Computing.

In essence, a quantum computer is a supercomputer cooled to near absolute zero temperatures. This temperature lets the processor achieve processing power that is not possible under natural conditions.


Image by research.ibm.com

We think that quantum computers are extremely fast, but in reality, they aren’t faster than the traditional ones.

The extreme cold allows the subatomic particles to arrange in a specific way and enable the processors to perform calculations that are in theory impossible for computers we use every day. For example, quantum computers would be able to simulate molecules, protein folding, and logistics optimization.


Quantum computers have two specific properties:

Superpositioning and Entanglement

Traditional computers deal with information on a binary basis – a series of 0s and 1s. Quantum computers do the same thing using qubits – superpositions of 0 and 1. Qubits can exist in two states at the same time.

When the qubits are connected into a system, their number grows at an exponential rate. One qubit will have two states; two will have four states and so on.

Entanglement is when two qubits are entangled. When a value of one qubit is measured, automatically the value of the second qubit is known too. The entanglement of all qubits will give every possible state.


How can Quantum Computing Affect Bitcoin?

Quantum computers are really great at solving cryptographic problems.

But where do we find cryptography in Bitcoin?

Each Bitcoin wallet has a private and a public key. The public key serves as the address to which you get funds, and it is created from your private key. The private key is the password you use to send funds.

Each transaction is signed with an elliptic curve signature scheme. This signature proves that you are the owner of this private key without telling others about it on the network. The algorithm used to create the public key from a private one is relatively easy but trying to reverse it is almost impossible.

Quite a number of people believe that a single quantum computer would be able to take over 51% of the network and perform an attack on Bitcoin.

Luckily, the reality is much brighter. ASIC miners that are used to mine Bitcoin will be still in use even if quantum computers existed in the future. It would be really hard for quantum computers to perform the 51% attack. Actually, we should be more cautious of the ability of quantum computers to extract private keys from public keys.

Our everyday computers don’t have the resources to do that now, so the elliptic curve signature technology is safe. The cost to do so would be immense.

A simple computer would need to do 2128 or 340,282,366,920,938,463,463,374,607,431,768,211,456 operations to extract the private key, while a quantum computer using Shor’s algorithm would manage to extract one in just 1283 or 2,097,152 operations. Sounds amazing, doesn’t it?

 

Will Quantum Computers Kill Bitcoin?

The answer is No.

We are still many years away till we see a quantum computer capable enough to extract private keys on the Bitcoin network. So, naturally, Bitcoin is relatively safe.

On the other hand, we could implement new solutions to make Bitcoin Quantum Computer-proof.

Addresses used one time

A rather impossible solution would be to use Bitcoin addresses once. According to this, the public address would be only visible when you start a transaction and when it ends up on the blockchain.

Change the algorithm of the Signature

This solution suggests that we should change the elliptic curve signature to an algorithm which should be quantum resistant.

A common suggestion is the Lamport signature which is larger than the elliptic curve one. Sadly, the issue is scalability even with the Lightning Network.

All in all, if any changes are made to the algorithm of the public key, Bitcoin would need to be soft-forked. Every user then should transfer their funds to the new address, and the funds left behind would be prone to theft.


What about other cryptocurrencies?

We already have teams that are building quantum resistant cryptocurrencies.

IOTA uses one-time Winternitz signatures to create a pair of keys. After sending the funds, addresses become unusable.

Nexus updates and plays with the keys after each transaction. The scheme is called the “Signature Chain”.

Hcash uses BLISS signatures to become quantum resistant.


Cryptocurrency and Quantum Computing?

We don’t usually hear about quantum computing and cryptocurrencies, but there are projects working on becoming quantum resistant. Even Ethereum had a proposal to allow different signature algorithms for each user.

Quantum computers are still a thing of the future and most projects have plenty of time to do their homework and prepare for their arrival.


This article was originally posted on Coincentral.com by Steven Buckho

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