|Originally posted by markkent
because of encryption. If someone is broadcasting something with an intent to allow only 1 or 0 copies then they will encrypt it so that only compliant hardware/software will be able to de-crypt it. By "compliant" I mean authorized hardware/software that follows the broadcasters intent.
Not just encryption--most importantly, authentication. A piece of equipment which wants to receive protected content (a "sink", like a recorder) must convince the piece of equipment which has that content (a "source", like a cable or DBS STB) that it is authorized to participate in DTCP. Once the two devices are satisfied with each other's credentials, they then exchange information (in an encrypted fashion) to determine the set of public keys that will be used to encrypt the MPEG-2 data before it's passed between them. You have to have the matching private keys to decrypt the data--only the device that requested it can make any sense of it.
If that initial authentication step is not successful, no protected video is placed on the cable to be captured. Even after it starts, every couple of seconds, the source issues a challenge that only the sink that authenticated the link can successfully respond to (to keep people from disconnecting the line after authentication to an authorized sink and connecting it to something else).
There are four levels of protection in DTCP (actually, they all stem from CGMS)--"Copy Freely", "Copy One Generation", "Copy No More" and "Copy Never". "Copy Freely" data is not encrypted and no authentication is performed before sending it. "Copy One Generation" data can be copied once by a compliant device, but the playback of those recordings must be marked "Copy No More", which no compliant device will record. "Copy Never" not only is not be to recorded by a compliant device (except a PVR, which isn't allowed to archive it, only to buffer it for pausing and rewinding, etc), it is protected by a second, much stronger form of authentication; recording devices other than PVRs are not factory-provisioned with the information that they'd require to pass that authentication--they basically can't even ask a source to send "Copy Never" content to them.
-- Mike Scott