Secure message transmission is of extreme importance in
today's information-based society. Stream encryption is a
practically important means to this end. This monograph is
devoted to a new aspect of stream ciphers, namely the
stability theory of stream ciphers, with the purpose of
developing bounds on complexity which can form part of the
basis for a general theory of data security and of
stabilizing stream-cipher systems.
The approach adopted in this monograph is new. The topic is
treated by introducing measure indexes on the security of
stream ciphers, developing lower bounds on these indexes,
and establishing connections among them. The treatment
involves the stability of boolean functions, the stability
of linear complexity of key streams, the period stability of
key streams, and the stability of source codes. Misleading
ideas about stream ciphers are exposed and new viewpoints
presented.
The numerous measure indexes and bounds on them that are
introduced here, the approach based on spectrum techniques,
andthe ten open problems presented will all be useful to
the reader concerned with analyzing and designing stream
ciphers for securing data.