PostgreSQL 11 Administration Cookbook

For really, really, really sensitive data

For even more sensitive data, you may never want the data to leave the client computer unencrypted. Therefore, you need to encrypt the data before sending it to the database. In that case, PostgreSQL receives already encrypted data and never sees the unencrypted version. This also means that the only useful indexes you can have are for use in WHERE encrypted_column = encrypted_data and for ensuring uniqueness.

Even these forms can be used only if the encryption algorithm always produces the same ciphertext (output) for the same plaintext (input), which is true only for weaker encryption algorithms. For example, it would be easy to determine the age or sex of a person if the same value were always ...