Location Privacy in Pervasive Computing	

Problems

The paper aims to solve the problem of users being able to benefit from
location based services and applications while at the same time retaining
their location privacy.

Strengths

(1) The paper presents a solution to preserve the location privacy of users of
location based systems that is based on pseudonyms. Pseudo-identities hide the
actual identities of the users of location based systems and allow them remain
anonymous. The paper discusses the merits, weaknesses and theextensions 
that allow this scheme to become effective.

(2) It discusses the concept of the mix zone that makes pseudonym anonymity of users
possible. The mix zone, in addition to regular routing nodes, consists of mixed 
nodes that rearrange the order of the messages so that outgoing messages cannot be 
linked with incoming ones. The mixed zones form the basis for the anonymity model
discussed in the paper. 

(3) The paper provides a quantifiable anonymity measure in the form of the anonymity
set which consists of all the users present in a mixed zone at a given time. Providing
a quantifiable measure is one of the most significant contributions of this paper 
as this allows a person to be able to differentiate between various systems in terms of
the quality of the anonymity they offer. The higher the size of the anonymity set, the 
better the system.

(4) The paper also discuss the constraints and drawbacks of the mixed zone model. The
mixed zone model is effective when the number of users are high. A high number of users
results in a bigger anonymity set which results in better privacy.

Weaknesses

(1) The experiment conducted by the researchers was in an environment where the number
of users of the mixed zones were fairly low. In this case, their solution was not very
effective and it was still possible to map locations to actual identities with a high
probability. The experiment should have been conducted under different conditions to 
validate the model.

(2) The researchers only did a cursory analysis of whether existing applications could
be adapted to use their prescribed anonymity framework that use anonymizing proxies. A more
detailed analysis on the practical use and implmentation of such a framework for existing
applications would have been highly beneficial.