The Cryptography and Security Group at the Computer Science Department is one of the leading research groups in cryptography in Europe and worldwide. Several of the group members are active in the quantum area, since quantum computers represent both a threat and an opportunity for the field of cryptography.
Most of the cryptographic algorithms that underlie the security of the Internet today (including methods based on factoring, discrete logarithm and elliptic curve) can be easily broken by (large enough) quantum computers. However, this does not mean that all of cryptography can be broken by quantum computers, and there are several cryptographic assumptions (code-based, lattices, isogenies, unstructured assumptions like hash functions, block ciphers, etc.) that even quantum computers cannot break.
In the realm of quantum security, two methods stand out. Quantum Key Distribution (QKD) leverages quantum phenomena for secure channels, while Post-Quantum Cryptography (PQC) relies on classical algorithms resilient to quantum attacks thanks to the assumptions listed above.
Our research group focuses on PQC, which offers distinct advantages. Unlike QKD, PQC is deployable on existing hardware and networks, thwarting future adversaries from decrypting sensitive data collected today. Furthermore, PQC extends beyond confidentiality and allows to build authentication systems lke digital signatures, necessary in systems like MitID.
Our research group leverages decades of experience in advanced cryptographic protocols to build novel cryptographic algorithms which are secure against quantum computers. Two notable examples are Picnic and FEAST, two post-quantum signature schemes that our researchers submitted respectively to the Post-Quantum Cryptography Standardization effort by NIST (the US National Institute of Standards and Technology). Those signature schemes are based on the “MPC in the head” approach, for which Aarhus has a leading position.
A second problem that must be solved is how to offer a quantum-computing service in a secure manner. Building a large quantum computer is a formidable technological challenge. For many years, not everyone will own a quantum computer, but will instead use cloud services to speed up specialized tasks. If everyone has to benefit from the potential of quantum computers, given the expected scarcity of quantum resources, it will be unavoidable that citizens and companies will need to delegate quantum computations to external providers.
So, quantum computers will need to handle data owned by other parties, and this raises security issues: can users trust that their data remain private? Can they trust the correctness of the results?
Researchers in Aarhus have decades of experience with secure multiparty computation protocols that enable joint computations and outsourcing of computation, and this can be extended to the quantum realm.
