Unique codes for marking packages for liquid food are generated with a header portion (40) containing non-encrypted code-definition data ([E], [G]) that represents the code structure and/or the code generation methodology, and a payload portion (41) containing encrypted payload data ([EP]). The encryption ensures that the code is sufficiently scrambled to make guessing and fraudulent code generation difficult. The payload data, before encryption, may be defined to be unique in each code, thereby also rendering the code unique. The payload data, before encryption, may also be structured so as to enable efficient search for the code in a database. When read from a package, the code may be processed by extracting the code-definition data ([E], [G]), identifying the payload portion (41), extracting the encrypted payload data ([EP]), re-creating the payload data by decryption, and searching the database for the code based on the payload data or one or more subsets thereof.