5C DTCP 
5 company Digital Transmission Content Protection. An HDTV copy-protection encryption method for devices connected via FireWire, this allows one of three copy states: copy always (all ATSC broadcast and "in the clear" QAM cable broadcasts); copy once (premium cable); and, copy never (pay per view, video-on-demand). Bidirectional system requires 5C chips in every device in an A/V system (in other words, a set-top box, a TV, and so on); the TV "requests" acknowledgment before allowing the signal to be viewed or recorded. Proposed and sponsored by Hitachi, Intel, Matsushita (Panasonic), Sony, and Toshiba--the five companies.