Retargeting Without Tracking

TL;DR

This paper introduces a privacy-preserving retargeting system that uses homomorphic encryption to enable targeted advertising without intrusive tracking, improving user control and ad freshness.

Contribution

It presents the first distributed, privacy-preserving retargeting scheme that maintains targeting effectiveness without systematic user tracking.

Findings

Efficient implementation of the proposed scheme.

Addresses ad frequency capping and freshness issues.

Provides increased user control and transparency.

Abstract

Retargeting ads are increasingly prevalent on the Internet as their effectiveness has been shown to outperform conventional targeted ads. Retargeting ads are not only based on users' interests, but also on their intents, i.e. commercial products users have shown interest in. Existing retargeting systems heavily rely on tracking, as retargeting companies need to know not only the websites a user has visited but also the exact products on these sites. They are therefore very intrusive, and privacy threatening. Furthermore, these schemes are still sub-optimal since tracking is partial, and they often deliver ads that are obsolete (because, for example, the targeted user has already bought the advertised product). This paper presents the first privacy-preserving retargeting ads system. In the proposed scheme, the retargeting algorithm is distributed between the user and the advertiser such that no systematic tracking is necessary, more control and transparency is provided to users, but still a lot of targeting flexibility is provided to advertisers. We show that our scheme, that relies on homomorphic encryption, can be efficiently implemented and trivially solves many problems of existing schemes, such as frequency capping and ads freshness.