A computer processing device for determining whether to allow or deny access to a database associated with the device is provided. The device is configured to determine the origin of data signed with a first key by comparing the key to one or more keys stored in a further database to identify the source of the data; search the database to determine one or more access rules associated with the source of the data, wherein the access rules define whether write access to the database is allowed or denied for the data; and allow or deny write access to the database based on the determined rule or rules.