![](bg8.png)
and XOR them with the symmetric key. Though, the
search space can be reduced by a large factor with ad-
ditional knowledge about the location of the receiver,
e.g. the country or state. Also, an attacker might
know even more about the node, e.g. if it is located
within a building thereby excluding rural areas. So,
by educated guessing, a large scale of irrelevant ad-
dresses can be extracted from the set of potential ad-
dresses. This is all assuming that the attacker already
knows the randomly generated key. To hinder an at-
tacker from getting the symmetric key for all the par-
ticipants in the network, it is recommended that every
partner in the network exchanges a unique key with
the sender. This leads to a more complex communi-
cation scheme but benefits the overall security of the
algorithm.
5 CONCLUSION
The experiments conducted in this paper showed, that
the overall mean tolerance of the LDEA* algorithm
lies well above the hypothesized three meters of tol-
erance. This is due to the underlying grid structure of
the What3Words world map. The varying sizes of the
”squares” lead to a divergence of tolerance within the
most northern or southern regions of the earth.
With regards to the LDEA* algorithm, the toler-
ance leads to a larger area of decryption. A poten-
tial sender may very well assume, that a receiver will
be able to decrypt the ciphertext, if encrypted with
the LDEA* algorithm. This assumption only holds,
when the GPS measurement equipment on the re-
ceiver side is accurate enough to fall within the region
of
3.9302m
2
= 1.9651m, as the tolerance applies to the
whole ”square”. Modern GPS receivers are well capa-
ble of achieving this level of accuracy by utilizing the
differential GPS technology, described in (Van Sickle,
2015). This allows a GPS receiver to calculate its po-
sition in difference to another fixed point, thus elim-
inating some of the artificial inaccuracies of the re-
ceivers.
With the LDEA* algorithm at hand, e.g. an IoT
sensor network is able to efficiently encrypt the data
shared between the communication partners, who op-
erate in a publish-subscribe scheme. Future work may
focus on the concrete implementation of a tamper-
proof GPS receiver, since this aspect is assumed as
given in this paper. Existing proposals by Pozzobon
et al.(Pozzobon et al., 2011) already give a theoretical
approach but lack an implementation of the system
itself.
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