# Now

Since 2010, I am a Cryptography & Security Expert for CryptoExperts in Paris !

# Before

I received a Ph.D. in 2008 under the direction of Prof. Serge Vaudenay, head of the Cryptography and Security Laboratory (LASEC) at EPFL, Switzerland. My main research areas cover block ciphers and their cryptanalysis. I then spent some time in Belgium where I worked as a consultant and researcher for Smals.

# Contact

Thomas Baignères - CryptoExperts
 41 boulevard des Capucines 75002, Paris, France +33 6 48 44 74 92 first.last @ cryptoexperts.com

### ECRYPT Workshop on Lightweight Cryptography

#### Posted in November 2011

I am part of the program committee of the 2011 edition of the ECRYPT Workshop on Lightweight Cryptography.

LC 2011 is organized by the UCL Crypto Group and sponsored by the SymLab and VAMPIRE virtual labs of the Network of Excellence in Cryptology - ECRYPT II. It will be held on November 28-29, 2011, in Louvain-la-Neuve in Belgium.

### Proving the Security of the AES Substitution-Permutation Network

##### Published in the Proceedings of SAC 2005

In this paper we study the substitution-permutation network (SPN) on which AES is based. We introduce AES*, a SPN identical to AES except that fixed S-boxes are replaced by random and independent permutations. We prove that this construction resists linear and differential cryptanalysis with 4 inner rounds only, despite the huge cumulative effect of multipath characteristics that is induced by the symmetries of AES. We show that the DP and LP terms both tend towards $$1/(2^{128}−1)$$ very fast when the number of round increases. This proves a conjecture by Keliher, Meijer, and Tavares. We further show that AES* is immune to any iterated attack of order 1 after 10 rounds only, which substantially improves a previous result by Moriai and Vaudenay.

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