AVS Forum banner

Status
Not open for further replies.
1 - 6 of 6 Posts

·
Registered
Joined
·
430 Posts
Discussion Starter #1
Is an HD signal broadcast encrypted or does the STB encrypt it based on some copy protection flag in the stream?

I've always assumed at the source. I know this question has been asked before, but I don't think it's ever been answered.


Is the stream compressed before or after the being encrypted? It must be encrypted before being compressed if the stream is broadcast encrypted. Otherwise, how could HDCP and 5C co-exist?


If it is encrypted by the STB, how will existing STBs behave when they receive a copy protected broadcast? Will they ignore the copy protection flag?


If it broadcast encrypted, how will existing STBs be able to deal with it at all, much less down convert it?
 

·
Registered
Joined
·
632 Posts
If the STB is to do a transparent overlay of guide or graphics it will have to decrypt.


I assume they will have to reencrypt before the content is output on a DVI port.


Actually most boxes will have to decrypt at they take the compressed DBS or OTA signal and output an uncompressed output - I assume you can not decompress while encrypted. (Not all OTA signals need to be free. Subchannels can be encrypted. )



I guess the low end boxes could take a encrypted signal and output it over FireWire/5C ports without decryption.



[This message has been edited by ADent (edited 07-26-2001).]
 

·
Registered
Joined
·
430 Posts
Discussion Starter #3
Joe,


Thanks for your response, although I didn't really get what I was after.

Quote:
Free to Air broadcast TV is supposed to remain unencrypted...
"Supposed" is the key word here. I remember that the ATSC standard was designed with copy protection in mind. I remember hearing mention of copy protection flag in the ATSC stream. Per this standard, is an HD broadcast supposed to be encrypted by the broadcaster or the STB?


One the reasons I was asking this question was because I own a Panasonic TU-DST50 STB. It is unclear whether this STB or the TU-DST51 supports 5C or how it will behave if it receives a copy protected signal via over-the-air or cable. Many owners of the TU-DST50 have avoided having their units serviced to fix the blue sparkles problem, in hope that the unit will continue to work even if broadcasters start to use copy protection.


I realize that DirecTV and Dish are closed systems. They can basically do anything they please, but I'm sure broadcasters cannot. Cable companies as well probably will standardize.


Does anyone have more info on the in and outs of how 5C encryption works? We all know that decryption will take place in the display, but again where will the encryption take place? How are the encryption keys exchanged?


[This message has been edited by belmore (edited 07-26-2001).]
 

·
Registered
Joined
·
50 Posts


For those DST50 owners who think they are better of for their STB lack 5c. This is a misconception, 5c-equiped devices contain digital circuit to descrypt the content.


Typically, prior to transmitting the encrypted content, the

sink device must be authenticated by the source device so that the source device can provide the "key" for which the sink device uses to decrypt the content. This process is called AKE (authentication and key exchane) as specified in DTCP protocol. During transmition, the source periodically

change the "key" it uses for encryption and communicates this information to the sink device. The sink device will

"recalculate" the new "key" for decryption. The roburstness of 5c makes hacking very difficult that why it is chosen.


So I suggest you should upgrade your DST50 to include 5c.

 

·
Registered
Joined
·
19,568 Posts
Quote:
If the STB is to do a transparent overlay of guide or graphics it will have to decrypt.

I assume they will have to reencrypt before the content is output on a DVI port.
That wouldn't necessarily be true, right? The digital connection could allow for the transmission of overlay data that will be handled by the display device couldn't it? As long as the overlay data doesn't have to iteraction with the underlying image data, and it doesn't, then that would work well enough I would think.


I don't know that that is the case, I'm just saying that it should be reasonably doable.


And it might be moot anyway, since the encryption used to get it to your STB might not be (probably won't be, right?) the one that is used between the STB and the display device so it would already be doing the decrypt/encrypt cycle anyway I would think.



------------------

Dean Roddey

The Charmed Quark Controller
[email protected]
www.charmedquark.com


If it don't have a control port, don't buy it!
 

·
Registered
Joined
·
1,270 Posts
You've raised a few good points. Much of this has already been covered by others, but I'll try to put things in perspective for you.


1) Free to Air broadcast TV is supposed to remain unencrypted since the companies using the RF spectrum for Free to Air TV and Radio are doing so with RF spectrum that was loaned to them by the American people. Cable and satellite are not Free to Air and can encrypt anything they want using whatever technology they chose.


2) Encryption can be applied at any stage, but is usually only done at the time of broadcast. Digital data is just bits. Encryption is just a fancy way to scramble bits. The current technology being used by Cable and Satellite is a broadcast encryption with a public - private key. For example, DirectTV takes an analog signal and converts it to digital. Then the digital data is encrypted. Now the encrypted data is sent to the satellite and finally down to your house. The STB was designed by DirectTV and knows how to unencrypted the data. This is all proprietary and it's federal offense to take apart your DirctTV STB in order to try to understand how it works.


3) Future Satellite and Cable STB will encrypt the raw HDTV data using a new format specified by the 5C or HDCP standards. This digital data will be sent to your display device. The display device will decrypt this data and display it only if the copyright holder allows it to do so. The other option is that S-Video outputs will be provided so that your current HDTV can be used with newer STB. One thing that will be missing are are RGB or HD component outputs. If these are present, they will be deactivated if any copy protected material is being received by the STB.


4) 5C and HDCP will coexist as a means for allowing a secure method for copying HD material and as a method for displaying HD material. In short, 5C will be used for devices that allow copying and HDCP will be used for display devices. There is nothing that really prevents either one from being used as either display or recording technologies, but it seems that there is a compromise being struck somewhere that is resulting in having both systems in place.

 
1 - 6 of 6 Posts
Status
Not open for further replies.
Top