L'utilit\`a di una teoria inutile-Crittografia, firma digitale e teoria   dei numeri
  The theory of numbers was supposed to be the less useful branch of mathematics. At the same time, cryptography was thought to be a military or a diplomatic issue. In this note we show how the two concepts are today strictly related and how this link affects our daily activities. 
Alfredo Esposito
math.HO