Section: New Results

Block cipher design and analysis

Block ciphers are one of the most basic cryptographic primitives, yet block cipher analysis is still a major research topic. In recent years, the community also shifted focus to the more general setting of authenticated encryption, where one specifies an (set of) algorithm(s) providing both encryption and authentication for messages of arbitrary length. A major current event in that direction is the CAESAR academic competition, which aims to select a portfolio of good algorithms.

In 2015, we helped to improve the state of the art in block cipher research in several ways:

• P. Karpman developed a compact 8-bit S-box with branch number three, which can be used as a basis to construct a lightweight block cipher particularly efficient on 8-bit microcontrollers [23].

In 2016, together with P.-A. Fouque, P. Kirchner and B. Minaud, P. Karpman designed a family of efficient provably incompressible symmetric primitives, which corresponds to a weak notion of white-box cryptography. The objective of such algorithms is that given an implementation of a certain target size, an adversary shouldn't be able to efficiently find a smaller implementation with comparable functionality. We introduced a security model that captures the behaviour of realistic adversaries and used this model to prove the security of a family of block cipher and a family of key generating functions. The corresponding paper was published at ASIACRYPT 2016 [13].