Quantum computing is ending with binary computing cryptographic algorithms, or not?

It is common to read or hear that current, or classical, cryptographic systems could become vulnerable once large-scale quantum computers are developed.

Now, I don’t have a PhD in Physics, so I would like to explain the term quantum computing in my own words. Quantum computing deals on quantum phenomena at the subatomic level, and in a quantum computing the minimum unit is called Qubit. When we talk about classic computing, minimum unit is one bit and it has two possible values, true or false. While a qubit you can have a superposition of 0 and 1 simultaneously, represented mathematically as α|0⟩ + β|1⟩, where α and β are complex numbers and |α|² + |β|² = 1. Or having it said in a different way, a qubit can represent multiple possibilities or values at once. Additionally, qubits can be entangled with other qubits, allowing correlations that are just not possible with a classical bit.

Some people might think that quantum computing in the long future, or even sci-fi, but nothing further from the truth, quantum computing is no longer a distant frontier—it’s a rapidly advancing reality that challenges our digital security.

Traditional encryption methods like RSA or ECC, rely on mathematical problems that are hard for classical computers but trivial for quantum machines. As scalable quantum systems emerge, the threat to public-key cryptography intensifies, prompting a global race toward quantum-safe solutions.

Shor's and Grover's Algorithms

Shor's algorithm

This is a quantum algorithm, created by Peter Shor in 1994. This algorithm can efficiently factor large composite numbers into their prime factors in polynomial time, an exponential speedup over classical algorithms. This results in significant implications for RSA cryptography, since it can break encryption that relies on the difficulty of factoring. The algorithm works by taking advantage of quantum properties like superposition and entanglement to find the period of a function, which is then used with the greatest common divisor (GCD) to find the prime factors.

Grover's Algorithm

Created by Lov Grover in 1996, Grover’s Algorithm enhances search capabilities in unsorted databases, providing a quadratic speedup over classical search algorithms, this allows a quantum computer to find a specific item in a dataset in roughly the square root of the time required by a classical search. One primary way to counteract Grover’s Algorithm is to double the key size of symmetric encryption schemes.

Therefore, many classical cryptographic algorithms, particularly public-key systems like RSA and ECC, are expected to become obsolete once large-scale quantum computers are available. However, there are algorithms that remain relatively resilient.

Symmetric-Key Algorithms

AES (Advanced Encryption Standard) -256 → still considered quantum-resistant. Why, because even with Grover’s algorithm, a quantum computer would need 2^128operations to brute-force it, which is still exponentially large.

Asymmetric-Key Algorithms

RSA-2048. Estimates suggest that breaking RSA-2048 would require millions of stable qubits, far beyond current technology. Therefore, this algorithm is considered safe today, although RSA-2048 is vulnerable to quantum computing in the future.

Hashing functions

SHA-3 family – also secure with larger output, as we already said, Grover’s algorithm gives a quadratic speedup: for an n-bit hash, it reduces the security from 2^n to about 2^(n/2). SHA-3 has key lengths of 224, 256, 384 and 512. Therefore SHA3-256 →≈ 128 bits, effective quantum security and SHA3-512≈ 256 bits→ effective quantum security.

In this blog, I wanted to briefly cover the quantum computing topic, cryptography and talk briefly into classical crypto-algorithms versus quantum computing.

This article will be the starting point for a next blog about post quantum cryptography !!

The views and opinions expressed in this article are solely my own and do not necessarily reflect those of Microsoft or Universidad Fidélitas. This content is provided for informational purposes only and does not represent the official positions, strategies, or endorsements of either organization.

References:

Nielsen, M. A., & Chuang, I. L. (2010). Quantum computation and quantum information (10th anniversary ed.). Cambridge University Press.

Schneider, J., & Smalley, I. (2025, June 10). What is quantum computing? IBM. https://www.ibm.com/think/topics/quantum-computing

Classiq. (2022, July 19). Quantum cryptography - Shor's algorithm explained. Classiq. https://www.classiq.io/insights/shors-algorithm-explained

Fortinet. (n.d.). Understanding Shor’s and Grover’s algorithms. Fortinet. Retrieved September 16, 2025, from https://www.fortinet.com/resources/cyberglossary/shors-grovers-algorithms

IBM. (n.d.). Asset gallery: Quantum innovation. IBM Newsroom. Retrieved September 16, 2025, from https://newsroom.ibm.com/media-quantum-innovation?keywords=quantum&l=100