A security controller controls secure processing of queries in an encrypted relational database. A query controller receives, from a client device, a secure query in a format of an encrypted token generated using a structured query language (SQL) query in a conjunctive query form, and sends an encrypted response to the secure query to the client device. A search engine generates the encrypted response to the secure query by initiating a search on the encrypted relational database, without decrypting the secure query and without decrypting the encrypted multi-maps. The encrypted relational database includes encrypted multi-maps corresponding to a relational database hosted at the client device, and an encrypted dictionary, based on structured encryption, using structured encryption, in lieu of using property-preserving encryption (PPE), and in lieu of using fully homomorphic encryption (FHE).