HRU (security)

The HRU security model (Harrison, Ruzzo, Ullman model) is an operating system level computer security model which deals with the integrity of access rights in the system. It is an extension of the Graham-Denning model, based around the idea of a finite set of procedures being available to edit the access rights of a subject ${\displaystyle s}$ on an object ${\displaystyle o}$. It is named after its three authors, Michael A. Harrison, Walter L. Ruzzo and Jeffrey D. Ullman.

Along with presenting the model, Harrison, Ruzzo and Ullman also discussed the possibilities and limitations of proving the safety of systems using an algorithm.

The HRU model defines a protection system consisting of a set of generic rights R and a set of commands C. An instantaneous description of the system is called a configuration and is defined as a tuple ${\displaystyle (S,O,P)}$ of current subjects ${\displaystyle S}$, current objects ${\displaystyle O}$ and an access matrix ${\displaystyle P}$. Since the subjects are required to be part of the objects, the access matrix contains one row for each subject and one column for each subject and object. An entry for subject ${\displaystyle s}$ and object ${\displaystyle o}$ is a subset of the generic rights ${\displaystyle R}$.

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