Multi-user Location Correlation Protection with
Differential Privacy
Lu Ou
†
, Zheng Qin
†
, Yonghe Liu
⊤
,HuiYin
†§
, Yupeng Hu
†
, Hao Chen
†
†
College of Information Science and Engineering, Hunan University, Changsha 410082, China
⊤
Department of Computer Science and Engineering, University of Texas at Arlington, Arlington 76013, USA
§
Department of Mathematics and Computer Science, Changsha University, Changsha 410022, China
Abstract—In the big data era, with the rapid development of
location-based applications, GPS enabled devices and big data
institutions, location correlation privacy raises more and more
people’s concern. Because adversaries may combine location
correlations with their background knowledge to guess users’
privacy, such correlation should be protected to preserve users’
privacy. In order to deal with the location disclosure problem,
location perturbation and generalization have been proposed.
However, most proposed approaches depend on syntactic privacy
models without rigorous privacy guarantee. Furthermore, many
approaches only consider perturbing the locations of one user
without considering multi-user location correlations, so these
techniques cannot prevent various inference attacks well. Cur-
rently, differential privacy has been regarded as a standard for
privacy protection, but there are new challenges for applying
differential privacy in the location correlations protection. The
privacy protection not only should meet the needs of users who
request location-based services, but also should protect location
correlation among multiple users.
In this paper, we propose a systematic solution to protect
location correlations privacy among multiple users with rigorous
privacy guarantee. First of all, we propose a novel definition,
private candidate sets which are obtained by hidden Markov
models. Then, we quantify the location correlation between two
users by using the similarity of hidden Markov models. Finally,
we present a private trajectory releasing mechanism which can
preserve the location correlations among users who move under
hidden Markov models in a period of time. Experiments on
real-world datasets also show that multi-user location correlation
protection is efficient.
Keywords—differential privacy, hidden Markov models,
location-based services, location correlation, the similarity of
hidden Markov models, private trajectory releasing
I. INTRODUCTION
In the big data era, with the popularity of smart phones
and other GPS enabled devices, the Location Based Service
(LBS) is an integral part of our life. This service can bring
convenience in our life. Therefore, in order to improve quality
of our life, big data institutions may improve the quality of
LBSs. At the same time, big data institutions will achieve
location information about each user and other related infor-
mation from location-based servers such as trajectories and the
user’s interest to improve the quality of LBSs. However, the
big data institutions are honest and curious. They may mine
some sensitive information about users, such as a location
correlation. For instance, there is a big data institution of
catering who wants to analyze restaurant interests for different
occupational groups. Through data mining, they may find that
users who are in the same occupational group are often at
the same location at the same time or the different time (as
shown in Figure 1). Furthermore, they may use this location
correlation to mine social correlations among the users. If
social correlations among multiple users are exposed, some
sensitive information may be inferred. Now we give a scenario
to explain this problem. As we can see in Figure 1, Betty
and Jerry are students (i.e., they are in the same occupational
group). Simultaneously, they are at same location (i.e., the
location correlation between Betty and Jerry) twice. Therefore,
adversaries may consider that Jerry and Betty are classmates
according to their background knowledge. Then if Jerry’s age
is leaked, Betty’s age will be known by adversaries too. Thus,
location correlation should be hidden to preserve the user’s
privacy.
Jerry
Betty
Mia
Andy
Student
Doctor
Fig. 1. User Location Trace about Different Occupational Groups
There are several works on location privacy protection.
But most of these existing approaches and solutions focus on
a single user’s privacy. Although a few works also consider
temporal correlations of one user, no location correlations
among multiple users.
To protect location correlations privacy among multiple
users with rigorous privacy guarantee, we propose a novel pri-
vate trajectory releasing mechanism which is based on hidden
Markov models (HMMs) to deal with this location correlation
disclosure problem. By using HMMs, a probable trajectory
set can be generated to cover every eventuality (trajectory).
And by using a similarity of HMMs, we can quantify the
locations correlation between two users in a period of time.
Then, based on the probable trajectories and the correlated
trajectories, we calculate a private candidate set which is used
to achieve differential privacy. Finally, an extended differential
privacy approach is proposed to protect the privacy.
We implement our approach on real-world datasets, and
the experimental results show that our approach could protect