  Security of complex systems is an important issue in software engineering.
For complex computer systems involving many actors, security protocols are
often used for the communication of sensitive data. Actor key compromise (AKC)
denotes a situation where the long-term secret key of an actor may be known to
an adversary for some reasons. Many protocols are not secure enough for
ensuring security in such a situation. In this paper, we further study this
problem by looking at potential types of attacks, defining their formal
properties and providing solutions to enhance the level of security. As case
studies, we analyze the vulnerabilities (with respect to potential AKC attacks)
of practical protocols, including PKMv2RSA and Kerberos, and provide solutions
to enhance the level of security of such protocols.
