  We model a private key`s life cycle as a finite state machine. The states are
the key`s phases of life and the transition functions describe tasks to be done
with the key. Based on this we define and describe the key authority, a trust
center module, which potentiates the easy enforcement of secure management of
private keys in hierarchical public key infrastructures. This is done by
assembling all trust center tasks concerning the crucial handling of private
keys within one centralized module. As this module resides under full control
of the trust center`s carrier it can easily be protected by well-known
organizational and technical measures.
