Mon, 29 Sep 2025 13:00 Cryptanalysis of an Efficient Signature Based on Isotropic Quadratic Forms by Henry Bambury (ENS Paris)

If lattice reduction is used today as the main cryptanalytic tool to attack lattice-based schemes, it can also apply to other schemes, for which lattices do not appear explicitly in the construction.

DEFI is an efficient signature scheme proposed by Feussner and Semaev, based on a structured version of quadratic form equivalence. It borrows ideas from both multivariate and lattice cryptography.

We present a key-recovery attack on DEFI. Our lattice-based attack is partially heuristic, but works on all proposed parameters: experimentally, it recovers the secret key in a few minutes, using less than ten (message, signature) pairs.

Speaker Bio:

I am a third year PhD student at ENS in Paris, under the supervision of Phong Nguyen. My work is mainly related to lattices and their use in cryptanalysis.

Venue: Online