So you think you’re safe?
We’re often told our privacy will be safe, because our data will be made anonymous. But Dorothy Denning and other computer scientists discovered in about 1980 that anonymization doesn’t work very well. Even if you write software that will only answer a query if the answer is based on the data of six or more people, there’s a lot of ways to cheat it. Suppose university professors’ salaries are confidential, but statistical data are published, and suppose that one of the seven computer science professors is a woman. Then I just need to ask “Average salary computer science professors?” and “Average salary male computer science professors?” And given access to a database of “anonymous” medical records, I can query the database before and after the person I’m investigating visits their doctor and look at what changed. There are many ways to draw inferences.
De-anonymization – Ross Anderson, Edge 2017
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