  We introduce a new model for evaluating privacy that builds on the criteria
proposed by the EuroPriSe certification scheme by adding usability criteria.
Our model is visually represented through a cube, called Usable Privacy Cube
(or UP Cube), where each of its three axes of variability captures,
respectively: rights of the data subjects, privacy principles, and usable
privacy criteria. We slightly reorganize the criteria of EuroPriSe to fit with
the UP Cube model, i.e., we show how EuroPriSe can be viewed as a combination
of only rights and principles, forming the two axes at the basis of our UP
Cube. In this way we also want to bring out two perspectives on privacy: that
of the data subjects and, respectively, that of the controllers/processors. We
define usable privacy criteria based on usability goals that we have extracted
from the whole text of the General Data Protection Regulation. The criteria are
designed to produce measurements of the level of usability with which the goals
are reached. Precisely, we measure effectiveness, efficiency, and satisfaction,
considering both the objective and the perceived usability outcomes, producing
measures of accuracy and completeness, of resource utilization (e.g., time,
effort, financial), and measures resulting from satisfaction scales. In the
long run, the UP Cube is meant to be the model behind a new certification
methodology capable of evaluating the usability of privacy, to the benefit of
common users. For industries, considering also the usability of privacy would
allow for greater business differentiation, beyond GDPR compliance.
