Protection in Operating Systems
A model of protection mechanisms in computing
systems is presented and its appropriateness 
is argued.  The "safety" problem for protection systems
under this model is to determine in a given situation 
whether a subject can acquire a particular right to
an object.   In restricted cases, it can be shown 
that this problem is decidable, i.e. there is an algorithm
to determine whether a system in a particular 
configuration is safe.  In general, and under surprisingly
weak assumptions, it cannot be decided if 
a situation is safe. Various implications of this fact are discussed.
CACM August, 1976
Harrison, M. A.
Ruzzo, W. L.
Ullman, J. D.
