Rethinking Stream Ciphers: Can Extracting Be Better Than Expanding?

In this paper the feasibility of an alternative approach to construct stream ciphers is discussed by revisiting an old friend, i.e. the popular one-time pad. The idea is that the rationale underlying the one-time pad --- which is notoriously unpractical in pure form due to the need of massive secret key exchange --- might be translated into practical cryptosystems that are different from conventional stream ciphers. In alternative to the usual pseudo- random keystream generation approach (expansion), a ``dual´´ approach based on sampling of a much longer sequence (extraction) could be conceivable nowadays due to the ready availability of sufficiently large memory resources, even in mobile devices such as PDAs, smartphones and tablets. The paper presents this idea, analyzing its pros and cons versus the classical one-time pad and conventional stream ciphers.