Cross-Layer Protocols for Backwards-Compatible Security Against Store-Now-Break-Later Attacks

• Applicant: Professor Dr.-Ing. Tibor Jager
• Subject Area: Security and Dependability, Operating-, Communication- and Distributed Systems
• Term: since 2026
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 574739425

Quantum computers enable exciting applications, but unfortunately, they also pose a threat to secure communication on the Internet. We are therefore currently in a transition phase in which new post-quantum schemes are replacing quantum-insecure classical cryptosystems. So far, research has focused on the development of new algorithms (for example, KEMs and digital signatures) that can be used as one-to-one replacements for existing schemes. While this approach makes sense for many applications, it is not sufficient on its own for a successful post-quantum transition, as practical considerations give rise to additional requirements that raise fundamental theoretical research questions: 1. How can we achieve security against so-called store-now-break-later attacks without having to wait for a slow standardize-implement-deploy process? 2. How can we achieve cryptographic agility for real-world applications, enabling the easy replacement of algorithms in the event of discovered vulnerabilities? 3. How can we achieve this in a backwards-compatible way with current devices, so that users in areas such as e-government or healthcare are not excluded if they do not have the latest state-of-the-art devices? These three requirements are essential for a successful post-quantum transition but are not fulfilled by the traditional approach of first developing, then standardizing, then implementing, then deploying new algorithms. This project explores new, foundational techniques to address the three challenges outlined above of the post-quantum transition. The approach is to consider a new category of cryptographic protocols, so-called cross-layer protocols. The project aims to develop a fundamental understanding of this new family of cryptographic schemes, which can provide an essential building block for a successful post-quantum transition. Cross-layer protocols are not intended as a replacement for standardized post-quantum cryptographic algorithms or protocols, but rather serve as complementary tools that can bridge the security gap during the ongoing transition, offering increased flexibility, agility, and backward compatibility.

• DFG Programme: Research Grants