Real cases
A case · you decide
Differ and Laplace and the school survey
Differ & Laplace — a 17-year-old publishing results from a school wellbeing survey
The club will publish how many students in each class answered yes to a sensitive question. Someone could compare this year's count with a version published after one student left.
Differ is the attacker: count-with-Alice minus count-without-Alice reveals Alice's answer.
Laplace is the noise-maker: a random amount, usually small and sometimes larger, of scale 1/ε.
How should the club publish the counts?
Privacy is not about hiding names. It is about what can be worked out.
Who made this?
“In reality, every technology reflects decisions made by designers, companies, and communities, and carries the values and power of those choices.”
- Who benefits from this technology?
- Whose needs are ignored?
A case · you decide
Budget and Epsilon count the spending
Budget & Epsilon — a 16-year-old answering questions about the survey all term
The club has set a privacy budget of ε = 1 for the term. Each published count uses ε = 0.1. By November they have answered 10 queries.
Budget is the accountant: 10 × 0.1 = 1.0.
Epsilon asks the trade-off question each time: how private, how accurate, and who could be re-identified?
A teacher asks for one more count. What should the club say?
Every answer leaks a little. The budget decides how little.
Who made this?
“In reality, every technology reflects decisions made by designers, companies, and communities, and carries the values and power of those choices.”
- Who benefits from this technology?
- Whose needs are ignored?