in the art viz m naor and o reingold u201c from unpredictability to indistinguishability a simple construction of pseudo random functions from macs u201d advances in cryptology crypto 39 98 lncs 1462 pp 267 282 1998 m bellare a desai e jokipii and p rogaway u201c a concrete security treatment of symmetric encryption u201d proceedings of the 38th symposium on foundations of computer science ieee 1997 pp 394 403 the fact that these elements e i 91 are unpredictable means that enough of their u03bb bits remain unknown so that the probability of the event e i a is negligible in the preferred embodiment of this invention each unpredictable element e i 91 is obtained bymultiplication modulo 2 u03bb of the element index i and the secret random number r 0 80 in this preferred embodiment when encryption is performed sequentially each element of the sequence e i 1 where i u2267 1 is generated from the previous element e i by modular 2 u03bb addition of the secret random number r 0 the first element of the sequence being the secret random number r 0 itself namely e 1 r 0 it should be appreciated bythose skilled in the art and is a further aspect of this invention that the unpredictable elements 91 and the combination operation 92 can be obtained in other ways that do not depart from the spirit and scope of the present invention as set forth in the claims in an alternate embodiment of this invention the unpredictable elements e i are the elements of the linear congruence sequence defined by e i a i u00d7.