Now suppose a malicious user (often termed an ''adversary'') wants to find whether Chandler has diabetes or not. Suppose he also knows in which row of the database Chandler resides. Now suppose the adversary is only allowed to use a particular form of query <math>Q_i</math> that returns the partial sum of the first <math>i</math> rows of column <math>X</math> in the database. In order to find Chandler's diabetes status the adversary executes <math>Q_5(D_1)</math> and <math>Q_4(D_1)</math>, then computes their difference. In this example, <math>Q_5(D_1) = 3</math> and <math>Q_4(D_1) = 2</math>, so their difference is 1. This indicates that the "Has Diabetes" field in Chandler's row must be 1. This example highlights how individual information can be compromised even without explicitly querying for the information of a specific individual. | Now suppose a malicious user (often termed an ''adversary'') wants to find whether Chandler has diabetes or not. Suppose he also knows in which row of the database Chandler resides. Now suppose the adversary is only allowed to use a particular form of query <math>Q_i</math> that returns the partial sum of the first <math>i</math> rows of column <math>X</math> in the database. In order to find Chandler's diabetes status the adversary executes <math>Q_5(D_1)</math> and <math>Q_4(D_1)</math>, then computes their difference. In this example, <math>Q_5(D_1) = 3</math> and <math>Q_4(D_1) = 2</math>, so their difference is 1. This indicates that the "Has Diabetes" field in Chandler's row must be 1. This example highlights how individual information can be compromised even without explicitly querying for the information of a specific individual. |