Symmetric Ciphers For Emerging Applications

• Applicant: Professor Dr. Gregor Leander
• Subject Area: Security and Dependability, Operating-, Communication- and Distributed Systems
• Term: from 2017 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 326921743

Nowadays, everyone - constantly and mostly unnoticed - uses cryptographic algorithms in daily life. Examples include, but are certainly not limited to, browsing the internet, withdrawing money from an ATM, talking on a mobile phone, and opening a car.Among all cryptographic solutions developed so far, symmetric cryptographic primitives - for which a same secret key is used for both encryption and decryption - are the most efficient ones. Compared to asymmetric schemes, symmetric schemes are often several magnitudes more efficient. Here, efficiency is not limited to speed, but can also be measured in terms of chip area, latency, energy, etc. This is the main reason why the major fraction of our sensible data is encrypted using symmetric cryptographic primitives.Besides lightweight cryptography, that is cryptography for highly constrained devices, one emerging field of applications for symmetric ciphers is located in the field of Fully Homomorphic Encryption Schemes (FHE), Multi-Party Computation (MPC) and Zero-Knowledge Proofs. Those techniques enable, in principle, a large variety of fascinating applications. However, in order to make those applications practical, it is important to improve the performance of the used building blocks.As it turns out the constraints imposed on the symmetric algorithm in the setting of FHE and MPC setting are quite different from the ones that are usually considered when designing symmetric ciphers. Here, the important metrics are the multiplicative size and the multiplicative depth. The aim of the project is to scrutinize in particular recent proposals for ciphers in the setting of FHE and MPC. The knowledge gained from analyzing the ciphers will later be used to determine design directions to finally build secure and performant ciphers meeting the needs of new applications.

• DFG Programme: Research Grants