[0. Summary]

1. Consider this SQL query running without Opaque’s oblivious mode, but only encryption mode. 

SELECT patients.name, diseases.treatment FROM patients, diseases WHERE patients.disease=treatment.disease;

This joins the tables patients (with fields name and disease) and diseases (with fields disease and treatment) by the attribute disease, in order to fetch for each patient the treatment. 

Consider the same threat model as in Opaque.
Give an example of a sensitive information that the attacker could learn by watching the distributed computation. Say what side information you assume your attacker has about the data and explain why it is reasonable that some attacker could have this side information.

P.S.: The syntax above is SQL, so if you need some help understanding it, the MySQL documentation is a good guide. 

2. Assume each disease has a unique entry in the patients table (in fact, it is a unique key). Give an algorithm that computes this join obliviously. It does not have to be optimal, but it has to be oblivious.