How Will Quantum Computing Impact Blockchain Technology?
By: Shaan Ray
Tags: Quantum Computing, Bitcoin, Bhq Contributors, Science, Blockchain

Cryptographers often voice the concern that blockchain technology could become obsolete upon the development of quantum computers (probably 10 to 15 years from now). They fear that once developed, quantum computers will be able to break the security mechanisms blockchains use (asymmetric cryptography and hashing). Though these concerns are somewhat justified, blockchain developers have time to proactively address the threat.

What is Quantum Computing?

To understand the security threat posed by quantum computers, it is important to understand how they differ from classical computers. A classical computer uses a base 2 numerical system: it understands, processes and communicates data exclusively using bits. Each bit can hold only one of two positions: 0 or 1. We can think of each bit as a light switch: it can either be on or off.

Quantum computers, on the other hand, use qubits which can hold two positions at once. (For example, a qubit could hold both a 0 and 1 at the same time). This phenomenon, known as superposition, is the secret weapon of quantum computing. Superposition decreases the number of operations required for the computer to solve a problem. Thus, quantum computers can handle multiple complex queries simultaneously.

A quantum computer’s ability to engage in more computations per second than a classical computer explains why many computer scientists believe that a quantum computer will be able to crack current cryptographic protocols with relative ease.

A Classical bit compared to a Quantum Bit or ‘Qubit’

Asymmetric Cryptography, Symmetric Cryptography, and Hashing

To gauge how, specifically, quantum computers will impact cryptography, it is worth understanding a few kinds of cryptography widely in use today. I have discussed cryptography and hashing previously. Here is a quick recap:

· Symmetric cryptography uses the same cryptographic key for encryption and decryption. This is similar to using the same key to lock the front door to your house in the morning, and to unlock it in the evening.

· Asymmetric cryptography, also called public-key cryptography, uses a pair of keys for each transaction: a public key and a private key. The public key encrypts a message, while the private key decrypts it. They must be used together to execute a transaction.

· Hashing algorithms scramble data into a unique string of letters and numbers that represents that specific data. Any given piece of untampered data will always produce the exact same hash.

Blockchains use two primary security tools: encryption via asymmetric cryptography, and hashing algorithms.

Asymmetric Cryptography Depends on the Difficulty of Factoring Large Numbers

Asymmetric cryptography algorithms, which secure blockchains, are based on prime numbers and factors. In every blockchain protocol, the public and private keys are both extremely large numbers that have been hashed into a series of smaller letters and numbers. Since finding the prime factors of an enormous number is virtually impossible for classical computers, blockchains are tamper-proof.