Convergent encryption derives the key from the file content itself and means an identical file encrypted on different computers result in identical encrypted files. This enables the cloud storage provider to de-duplicate data blocks, meaning only one instance of a unique file (such as a document, photo, music or movie file) is actually stored on the cloud servers but made accessible to all uploaders. A third party who gained access to the encrypted files could thus easily determine if a user has uploaded a particular file simply by encrypting it themselves and comparing the outputs.