  We consider the problem of constructing an unconditionally secure cipher with
a short key for the case where the probability distribution of encrypted
messages is unknown. Note that unconditional security means that an adversary
with no computational constraints can obtain only a negligible amount of
information ("leakage") about an encrypted message (without knowing the key).
Here we consider the case of a priori (partially) unknown message source
statistics.
  More specifically, the message source probability distribution belongs to a
given family of distributions. We propose an unconditionally secure cipher for
this case. As an example, one can consider constructing a single cipher for
texts written in any of the languages of the European Union. That is, the
message to be encrypted could be written in any of these languages.
