The architecture of classical computers has been the driving force behind the digital revolution and the rise of modern computing. They function using a series of binary bits, ones and zeros, and on and off. On the other hand, a quantum computer uses the idea of superposition from quantum mechanics, wherein the state can be a combination of one and zero. This enables interactions and algorithms that would not be possible on a classical computer because of the fundamentally unique architecture of quantum bits (qubits).

Quantum cryptography is the study of methods of encryption and transmission of data using quantum mechanical methods, exploiting the uncertainty of the state. Currently, experts predict we are 20 to 50 years away from the “quantum age,” in which quantum computers would be powerful enough to break widely used algorithms such as RSA, which is widely used across the web, ranging from emails, VPNs, and EEC, which is used for cryptocurrency and web encryption. Therefore, the development of quantum cryptographic methods is crucial to improving data security in this quantum future.

Much of the worry about the rise of quantum computing comes from the impacts of Shor’s algorithm on RSA encryption. It uses a relatively simple mathematical algorithm — factoring the product of large prime numbers — through a public (anyone can see) key for encryption and a private (hidden) key to decrypt and view the data. Complexity arises from the enormous size of the prime numbers, because as they grow larger, it gets more difficult to factor their product and compute. This size works at repelling classical computers, which solve using ones and zeros. However, this becomes problematic when quantum-based algorithms are applied.

Quantum computers utilize the quantum properties of superposition and parallelism, where quantum algorithms cause incorrect paths to cancel out while the correct ones are amplified because the algorithm alters the respective probabilities. This is akin to how noise-cancelling headphones produce waves that cancel background audio waves. The correct result becomes more likely because of the wave superposition of quantum mechanics. This gives them the capacity to factor large numbers much faster than classical algorithms. Just how much faster? It would take a classical computer billions of years to crack the RSA algorithm. However, combining Shor’s factoring algorithm with the unique architecture of a powerful quantum computer, it could be done in a matter of hours.

While quantum algorithms with sufficient processing power would render RSA obsolete, there are many remedies to this, many of which are already in effect. For example, the AES algorithm is used for military-grade encryption and highly sensitive information. Grover’s quantum algorithm would enable a quadratic speedup in cracking AES encryption. However, because of its sturdiness, this would only leave the weaker, 128-bit version less effective, albeit far better than RSA. The stronger, 256-bit version would still be entirely viable, with the quantum speedup only having a moderate impact. There are also classical algorithms being devised specifically for the quantum age. One actively-researched algorithm is lattice-based cryptography using lattice mathematical structures — a type of high-dimensional grid — for encryption sturdy enough for a post-quantum age.

Quantum cryptography will fundamentally alter the entire landscape of classical encryption algorithms, requiring stronger versions of quantum-resistant algorithms such as AES. However, it also enables many new forms of encryption through the advent of quantum algorithms to keep information even more secure for the future.