1. Sean Mulvany, Ph.D Technology Transfer Case Manager
Privacy ensuring recommender system
Sean Mulvany, Ph.D
Technology Transfer Case Manager
Trinity Research & Innovation
Trinity College Dublin, the University of Dublin, Dublin 2, Ireland.

@seanmulvany

2. OVERVIEW
Currently
Users rate some items (directly, by clicking, buying, viewing, pairwise comparison etc), task of the recommender is to predict their ratings for other items of interest.
The pattern of item ratings supplied by a user by itself can identify that user, even if not explicitly tagged with a user id. Already demonstrated in the wild e.g. netflix/IMDB de-anonymisation attack.
Privacy/data protection concerns, e.g. in EU, mean:
User ratings data, even if anonymised by removing user IDs, cannot be used for other purposes or sold to third parties
Inadvertent release of ratings data, e.g. due to mishap or hacking, carries excessive privacy and reputational risk
Growing user unease

3. BLC Private Recommender
BLC Uses Shared Identities (“nyms”) For Privacy
Users rate items as before, e.g. in app or browser.
But now app/browser selects a shared identity/nym and submits ratings using this
The system only ever sees/stores (nym, item, rating) information.
A “hiding in the crowd” type of privacy, which comes with strong guarantees.
Even if nym used by user is inadvertently disclosed, items rated by user are not revealed.
Easily understood by users
No degradation in prediction performance, no need to add “noise” to ratings to gain privacy

4. Excellent Recommendation Performance
Shared Identities Improve Prediction Performance As Well As Privacy
It is already widely recognised, e.g. by advertisers, that users can be grouped into categories by taste, demographic, location etc
Grouping boosts the prediction performance of collaborative filters, if groups are chosen well, since users sharing a group are much more alike than the general population.
State of the art performance “out of the box”, no fine-tuning

5. Thank You http://www.tcd.ie/research_innovation/