  As the number of devices being interconnected increases, so does also the
demand for (lightweight) security. To this end, Physical Unclonable Functions
(PUFs) have been proposed as hardware primitives that can act as roots of trust
and security. Recently, a new type of PUF based on Carbon NanoTubes (CNTs) has
been proposed. At the same time, attacks and testing based on direct electrical
probing appear to be moving towards non-invasive techniques. In this context,
this work attempts to examine the potential for practical non-invasive probing
attacks against the CNT-PUF, a novel PUF based on CNTs. Our results indicate
that direct probing might potentially compromise the security of this PUF.
Nevertheless, we note that this holds true only in the case that the attacker
can directly probe the wire corresponding to the secret value of each CNT-PUF
cell. Thus, we can conclude that the examined CNT-PUFs are rather resilient to
direct probing attacks, that non-invasive probing methods appear to be
promising for testing such PUFs, and that, in order for the attacker to gain
the full-length value of the secret, all the relevant channels would need to be
probed. Nevertheless, as our work proves, practical non-invasive attacks
against the CNT-PUF are feasible and adequate countermeasures need to be
employed in order to address this issue.
