LocX is a system that provides improved location privacy for users of geo-social applications. It decouples a user's real-world location from the location data shared with servers through the use of coordinate transformations and encryption. Users generate mappings between transformed locations and encrypted indexes (L2I) that are stored on an index server via proxies, as well as mappings between indexes and encrypted location data (I2D) stored directly on a data server. This allows users to query for friends' location data based on transformed coordinates while preserving the privacy of their real locations.

1. B. AMALA
(CSE)

2. Introduction
Using geo-social applications, such as FourSquare,
millions of people interact with their surroundings
through their friends and their recommendations.
Without adequate privacy protection, however, these
systems can be easily misused
LocX, a novel alternative that provides significantly-
improved location privacy

3. Popular geo-social applications :

4. Privacy:
“New technologies can pinpoint your location at any
time and place. They promise safety and convenience
but threaten privacy and security”
PleaseRobMe.com- sarcastic site
criticizing putting personal information
online

5. Privacy in Existing system:
• Introducing uncertainty or error into location data.
• Relying on trusted servers or intermediaries to apply
anonymization to user identities and private data.
• Relying on heavy-weight cryptographic techniques.

6. LocX
To address this challenge LocX, a novel alternative that
provides significantly improved location privacy without
adding uncertainty into query results or relying on strong
assumptions about server security.
The key insight is to apply secure user-specific, distance
preserving coordinate transformations to all location data
shared with the server.

7. Objective:
To build a system which enables the users to query for
friends data based on location, while preserving
privacy of location.
It should support
• Point query
• Circular range query
• Nearest-neighbor query

8. System Requirements:
The key requirements for ideal location privacy services
 Strong location privacy
 Location and user unlinkability
 Location data privacy

9. Basic Design :
1) Alice and Bob exchange their secrets
2) Alice stores her review of the restaurant(at (x, y)) on the server under
transformed coordinates
3) Bob later visits the restaurant and queries for the reviews on
transformed coordinates, and
4) decrypts the reviews obtained.

10. Limitation of basic design
The server can uniquely identify the client devices.
The server can associate transformed co-ordinates to
the same user.
Such associations can break the transformations.
One approach to resolve these limitations is to route
queries through anonymous routing system .

11. Overview of LocX
•LocX builds on top of the basic design to overcome its
limitations
• Locx splits the mapping between location and data into
two pairs
mapping from transformed location to an encrypted
index ( L2I)
mapping from index to encrypted location data (I2D)
•Users store and retrieve the L2Is via untrusted proxies

12. Decoupling a location from its data
 Location data data(x,y) corresponding to the real-world
location (x, y) is stored under (x, y) on the server.
 But in LocX, the location (x, y) is first transformed to
(x1, y1), and the location data is encrypted into
E(data(x,y)).
 Then the transformed location is decoupled from the
encrypted data using a random index i via two servers
as follows:
1) an L2I = [(x, y),E(i)],which stores E(i) under the
location coordinate (x, y), and
2)an I2D = [i,E(data(x,y))], which stores the encrypted
location data E(data(x,y)) under the random index i.

13. Design of LocX
1) Alice and Bob exchange their secrets.
2) Alice generates and L2I and I2D from her review of
the restaurant (at (x, y)), and stores the L2I on the index server via a proxy.
3) She then stores the I2D on the data server directly.
4) Bob later visits the restaurant and fetches for L2Is from his friends by sending the
transformed coordinates proxy.
5) He decrypts the L2I obtained and then queries for the corresponding I2D.
6) Finally Bob decrypts Alice’s review.

14. Proxying L2Is for location privacy:
 Users store their L2Is on the index server via
untrusted proxies
 These proxies can be any of the following : email
servers in a user’s work places, a user’s home and office
desktops or laptops.
Compromising these proxies by an attacker does not
break users’ location privacy, as the proxies also only
see transformed location coordinates and hence do
not learn the users’ real locations.

15. Storing L2I on the index server
 To perform this, the user transforms her real world
coordinate (x, y) to a virtual coordinate (x1, y1).
 The user then stores this L2I, [(x, y), Esymm(i)], at
the transformed coordinate on the index server via
a proxy.
 The L2I is small in size as it always contains the
coordinates and an encrypted random index.

16. Storing I2Ds on the data server
 This is secure because the data server only sees the
index stored by the user and the corresponding
encrypted blob of data.
 In the worst case, the data server can link all
the different indices to the same user device.
 The content of I2D is application dependent.

17. BUILDING APPLICATIONS USING LOCX
 Location-based reminders
 Location-based recommendations.
 Friend locator

18. Conclusion :
LocX, users efficiently transform all their locations
shared with the server and encrypt all location data
stored on the server using inexpensive symmetric
keys. Only friends with the right keys can query and
decrypt a user’s data.