1. A method for a Radio Frequency Identification (RFID) system to cause an RFID tag having a first parameter to execute an instruction, the method comprising: sending a first command to the tag; receiving from the tag at least an identifier and an encrypted version of the first parameter; determining a key using the received identifier; recovering the first parameter from the encrypted version using the key; sending, at a first time, to the tag a single second command including the first parameter and a tag instruction; and causing the tag to execute the tag instruction upon verifying the first parameter.