Join operations on encrypted database tables

A non-transitory computer readable storage medium embodying a computer program for performing a method, said method comprising:

• a server storing in an in-memory database, a first encrypted table and a second encrypted table encrypted according to a non-deterministic and searchable first encryption scheme;
• the server receiving from a client, a join token based upon a query including a join operation and a predicate attribute constraint;
• an in-memory database engine of the server, prior to joining the first encrypted table and the second encrypted table, separately searching the first encrypted table according to the predicate attribute constraint to reveal only rows of the first encrypted table fulfilling the predicate attribute constraint and searching the second encrypted table according to the predicate attribute constraint to reveal only rows of the second encrypted table fulfilling the predicate attribute constraint, the engine generating an intermediate construction including only rows of the first encrypted table and the second encrypted table fulfilling the predicate attribute constraint, the intermediate construction encrypted according to a different encryption scheme;
• and
• the server communicating to the client, the rows of the first encrypted table and the second encrypted table fulfilling the predicate attribute constraint.

A computer system comprising:

• one or more processors;
• a software program, stored in memory, executed on said computer system, the software program configured to cause an in-memory database engine to:
• store in an in-memory database, a first encrypted table and a second encrypted table encrypted according to a non-deterministic and searchable first encryption scheme;
• receive from a client, a join token based upon a query including a join operation and a predicate attribute constraint;
• search, prior to joining the first encrypted table and the second encrypted table, the first encrypted table according to the predicate attribute constraint to reveal only rows of the first encrypted table fulfilling the predicate attribute constraint, and separately search the second encrypted table according to the predicate attribute to reveal only rows of the second encrypted table fulfilling the predicate attribute constraint, and generate an intermediate construction including only rows of the first encrypted table and the second encrypted table fulfilling the predicate attribute constraint, the intermediate construction encrypted according to a different encryption scheme;
• and communicate to the client, the rows of the first encrypted table and the second encrypted table fulfilling the predicate attribute constraint.