If we take two random circulant matrices A of dimension N × N and B of
dimension M ×M and calculate P = AGB where G is an N ×M base matrix,
then it is difficult to get A and B from P and G over a chosen ring. Where
F(A, B) = AGB serves as a Trapdoor function. In publickey cryptography
with matrices in the trapdoor function P = AGB ,if G is chosen such that
doubly circulant matrix |Gc| = 0, then it is difficult to find the circulant matrices
A and B