International Association
for Cryptologic Research

This paper investigates the mathematical structure of the ``Isomorphism of Polynomial with One Secret\'\' problem (IP1S). Our purpose is to understand why for practical parameter values of IP1S most random instances are easily solvable (as first observed by Bouillaguet et al.).

We show that the structure of the problem is directly linked to the

structure of quadratic forms in odd and even characteristic. We describe a completely new method allowing to efficiently solve most instances. Unlike previous solving techniques, this is not based upon Gröbner basis computations.