t. An important aspect of cryptography with matrices is that given
N ×N matrix P over a field F find a class of matrices G over F such that the
associated doubly circulant matrix Gc is singular in order that the equation
AGB = P in circulant matrices A, B has infinitely many solutions. The aim
of this note is to present such a class of matrices G. We also present a direct
method of finding the inverse of a symmetric circulant matrix of order n,
a b b ... b
where a + (n − 1)b = 0.
K