The paper supports a debate concerning the meaning and the importance of redundancy and ergodicity in cryptography. The discussion is mainly organized around a very thought-provoking enciphering method, running-key cipher. The paper comes with a new view of running-key method which permits to resume and extend it for ergodic sources in order to provide good quality key generators for cryptography. We first apply the running-key method on natural language and then we extend it on logistic map. Finally some conclusions are drawn even for image enciphering.