//get inverse of encryption key for decryption
static GeneralMatrix GetInverse(GeneralMatrix key)
{
GeneralMatrix invKey = key.Inverse();
//calculate determinant to the power of 30
double det = key.Determinant();
double zDet = Math.Pow(det, 30);
//multiply each value by det^30 and mod31 that value
for (int i = 0; i < invKey.RowDimension; i++)
{
for (int j = 0; j < invKey.ColumnDimension; j++)
{
var temp = (invKey.GetElement(i, j) * zDet) % 31;
invKey.SetElement(i, j, temp);
}
}
Console.WriteLine("3x3 decryption matrix successfully created from key.txt");
return invKey;
}