Quantum Computing and Cryptography: What You Need to Know

Large-scale quantum computers are not here yet, but quantum computing is one of today’s hottest research fields in the technology world. IBM launched the IBM Q Experience prototype five-qubit machine in the cloud in 2016 and made it available for the world to use, learn from and explore. A year later, IBM added a second device with 16 qubits and announced it had successfully built and tested two new machines. One is a 20-qubit machine for clients, and the other is a prototype with 50 qubits, which will be the basis of future IBM Q systems.

With their vast increase in computing power, quantum computers promise to revolutionize many fields, including artificial intelligence (AI), medicine and space exploration. Quantum computing also holds the potential to bring significant advances to the world of cybersecurity.

Despite the expected benefits, however, much of today’s rhetoric focuses on the risks this technology could pose to widespread security practices, such as encryption. It’s likely that these risks are a decade or more away from being immediate threats, since large-scale quantum computers will not be available for commercial use for quite some time. However, it is important to understand what these risks are and why they exist — so we may begin considering ways to future-proof our systems.

Quantum Computing 101

Let’s begin by taking a look at how quantum computing works. Classical computers encode information in bits, which take the value of 1 or 0, while quantum computers are based on qubits. This technology adheres to two key principles of quantum physics: superposition, which means a qubit can represent both 1 and 0 simultaneously, and entanglement, which means the state of one qubit can be correlated with the state of another. These two principles enable quantum computers to solve complex problems that are beyond the capabilities of today’s computers.

Quantum Computing Versus Today’s Cryptography

Due to their ability to solve much more complex problems in far less time, large-scale quantum computers have the potential to severely impact cryptography. However, the degree of impact varies depending on the type of cryptographic algorithms used.

Asymmetric cryptographic algorithms, such as RSA and Diffie-Hellman, base their security on the fact that factoring large numbers and calculating discrete logarithms are tough mathematical problems. In fact, factoring a large number can take thousands of years — even with today’s most powerful computers. Unfortunately, this changes when running Shor’s algorithm, which can factor large numbers in days (or even hours), on a quantum computer.

Symmetric algorithms, such as Advanced Encryption Standard (AES), do not face the same existential threat as asymmetric algorithms, but the key sizes need to be doubled to provide the same level of protection. This is because Grover’s algorithm running on a quantum computer could provide a quadratic improvement in brute-force attacks on symmetric encryption algorithms.

What’s Next?

What can security professionals do in response to these risks? First and foremost, it is important to remember that the impact of quantum computing on cybersecurity will likely not be felt for many years. Right now, one important step is to understand the nature of these potential risks so that we can prepare to address them. There are also defensive measures being developed as we speak (e.g., post-quantum cryptography) and research being conducted to determine how quantum computing can be used to improve cybersecurity capabilities far beyond what is possible today.

The aforementioned risks are only part of the much larger story of quantum computing’s impact on the security world. The other side of the coin is its potential to revolutionize our capacity to safeguard business-critical and personal data.

Walid Rjaibi

CTO, IBM Security Guardium