Universal Encryption of Individual Sequences Under Maximal Leakage

We consider the Shannon cipher system in the framework of individual sequences and finite-state encrypters under the metric of maximal leakage of information. A lower bound and an asymptotically matching upper bound on the leakage are derived, which lead to the conclusion that asymptotically minimum leakage can be attained by Lempel-Ziv compression followed by one-time pad encryption of the compressed bit-stream.