Ming Ding | Information Security and
Privacy Group | Data61, CSIROWhat is re -identification? –Information bits
•A typical Australian person is protected by 25 bits against re -identification
•We only need 25 bits to generate unique IDs for the entire Australian population
(225>22.5million )
➢E.g., the information bits of “gender” ≈ 1 bit (Female=>0, Male=>1)
➢E.g., the information bits of “month and day in date of birth” ≈ 9 bits (decimal -to-binary mapping of day index,
the 365 -th day =>101101101)
➢E.g., the information bits of “driver license number” / ”Medicare card number” > 25 bits
•Once an adversary knows enough information about an individual (e.g., > 25 bits), an
Australian individual can be re -identified from a dataset
•When being asked whether you own your current property (1 -bit information) during a phone
call with some Solar energy company, you may want to say “I’d rather not disclosing this
private information”