A method, computer program product, and data processing system for secure automated dispensing of prescription medications are disclosed. A preferred embodiment of the present invention utilizes broadcast encryption to encrypt a prescription for storage on a machine-readable medium that is pre-written with a key management block (KMB). The KMB encodes a session key needed to read from or write to the medium. Each prescription-writing device and medication dispensing device is assigned a unique set of device keys, which are used to recover the session key from the medium. Only authorized devices are able to recover the session key from a medium's KMB. Thus, only authorized devices may read or validly write prescriptions from/to the machine-readable medium. Hence, only authorized providers can write fillable prescriptions and only authorized dispensers can dispense medications to fill those prescriptions.