1. A method for execution by a controller, comprising: receiving an encrypted signature from a tag associated with an item; determining a dynamic parameter, the dynamic parameter being a current time or a current location of the controller; obtaining a key based at least in part on the dynamic parameter; decrypting the signature with the key to obtain an identifier; validating the identifier by determining whether said signature has been previously received; and performing an action related to identification of the item, based on the identifier and the validation.