Post-Quantum Cryptography: So That Data Remains Secure In The Future

Quantum computers are by no means ready for series production. Still, the next challenge is already in the air: How can we prevent the exchange of information from becoming insecure in the future because, currently, widespread encryption methods are cracked with the help of quantum computers?

Using quantum algorithms to decode standard secure encryption methods, such as RSA, has already been possible. RSA and similar methods form the security basis for many Internet protocols, including HTTPS (Hypertext Transfer Protocol Secure) and TLS (Transport Layer Security). If it gets into everyday danger, there is an urgent need for action security specialists.

Quantum Algorithms Approach Problems Differently

The example of RSA shows where the problem lies. Such encryption methods use mathematical tasks that are difficult to solve – in the case of RSA, it is the prime number factorization. It is easy to form a product from two prime numbers. On the other hand, reversing the function, i.e., breaking down a reasonably large number into its prime number factors, requires immense computing effort. Because even powerful computers need several years to calculate, RSA is considered a secure encryption algorithm.

With the algorithm named after him, the mathematician Peter Shor showed back in the mid-1990s that the factorization problem could also be solved differently. Instead of trying out the numerous possibilities, the Shor algorithm looks for periodically repeating sequences in the set of possible solutions – a calculation that can only be solved quantum mechanically. In principle, however, the hardware is now available, and the calculation does not take seconds. Methods such as RSA would therefore be classified as insecure.

Post-Quantum Cryptography Is On The Way To Becoming A Standard

Encryption methods that quantum computers cannot decrypt will play an essential role in the future. As early as 2016, the American federal agency for standardization NIST (National Institute of Standards and Technology) announced a competition to find and promote the most promising post-quantum encryption methods. For a good year and a half, 69 suggestions were on the table, which were then evaluated by experts and tested as far as possible. Then, in June last year, the announcement: the authority considers four encryption algorithms suitable as a basis for standardization. Four other methods are also shortlisted.

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How Does Post-Quantum Cryptography Work?

The methods selected by NIST include CRYSTALS Kyber and CRYSTALS Dilithium, both of which work lattice-based (CRYSTAL = Cryptographic Suite for Algebraic Lattices). From the point of view of a snail, which always takes the shortest route to a head of lettuce in the middle of a field head of lettuce, he explains the “closest vector problem.” Roughly speaking, the CRYSTAL algorithms are based on lattice structures.

While it is relatively easy to place a point (i.e., information) near an intersection point, it is incredibly complicated to reverse this function to calculate the grid intersection point based on the placed point. Especially when it is a multi-dimensional grid, we are talking about 250 or more dimensions. Experts currently consider the lattice-based methods the most promising post-quantum cryptography variant. But methods that use other cryptographic systems – such as code-based, multivariate, or hash-based cryptography – also made it into the final round of the NIST competition.

Digression: Quantum Cryptography Is Not The Same As Post-Quantum Cryptography

There is a different concept behind quantum cryptography: quantum mechanical effects are used to encrypt data instead of mathematical calculations. For example, quantum keys consisting of polarized photons can be exchanged. If a stranger tries to measure the value and thus the key during the connection, the properties of the photons change. The sender and recipient notice this and do not use the intercepted key. Quantum cryptography methods are considered very secure and are already being used in practice. The quantum crypto processes are expensive, and the distance that can be bridged is relatively tiny.

Why Companies Should Care About Post-Quantum Cryptography

It is not unusual for encryption processes and security standards to become obsolete. But here, a paradigm shift is taking place. Post-quantum cryptography uses wholly different and, at the same time, mathematically highly complex approaches. Companies and solution providers should consider “crypto agility” when implementing it. This means that the cryptographic processes should not be a fixed part of specific solutions but can be supplemented and exchanged uncomplicated and solution-independent. As of today, post-quantum cryptography is suitable for use in parallel with proven methods.

The problem may not be acute yet, as quantum computers do not play a decisive role in practice. But in recent years, the technology has developed further, also thanks to international funding and research programs, some of which are extensive. Once they are used, even if only in specific areas, this will severely impact the security strategies that have been established up to now. Because, as described, a large part of it is based on encryption methods, which can no longer be classified as secure. It makes sense to think about a post-quantum security strategy now. Switching to a new technology takes years, and one must be well prepared.

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