  In 2002, Russell and Wang proposed a definition of entropically security that
was developed within the framework of secret key cryptography. An
entropically-secure system is unconditionally secure, that is, unbreakable,
regardless of the enemy's computing power. In 2004, Dodis and Smith developed
the results of Russell and Wang and, in particular, stated that the concept of
an entropy-protected symmetric encryption scheme is extremely important for
cryptography, since it is possible to construct entropy-protected symmetric
encryption schemes with keys much shorter than the keys. the length of the
input data, which allows you to bypass the famous lower bound on the length of
the Shannon key. In this report, we propose an entropy-protected scheme for the
case where the encrypted message is generated by a Markov chain with unknown
statistics. The length of the required secret key is proportional to the
logarithm of the length of the message (as opposed to the length of the message
itself for the one-time pad).
