ePrint Report: Cryptanalysis of an Efficient Signature Based on Isotropic Quadratic Forms
Henry Bambury, Phong Q. Nguyen
We present a key-recovery attack on DEFI, an efficient signature scheme proposed recently by Feussner and Semaev, and based on isotropic quadratic forms, borrowing from both multivariate and lattice cryptography.
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.