Analog protection

General	Audio-CD	Analog	Consoles	Storage	Obsolete
Ebook	Concepts	Software	Transmission

"I think its great, I really do. There's nothing anybody can do about it." - robbie williams on internet music piracy.

Digital technology is relativly recent. Analog has been used for decades, and will continue to be used for decades. Most televisions are still connected to VCRs and decoders by UHF lead. If its taking this long to switch to unmodulated formats, its going to take far longer to switch to digital. Analog will always be used, even if its just to drive a speaker.

The effect of analog technology on DRM is intresting. Unlike digital, analog cannot be encrypted. There is a loose equivilent, scrambling, but its very insecure. Analog was also not designed for DRM. All analog protection systems are improvised, with all the incompatability problems that implies. Without encryption and a key license there is nothing demanding analog equipment recognises or respects DRM. Analog is also so cheap and easy anyone with moderate electronics skills can build it. These factors allow one of the most popular attacks, "The Analog Hole".

Analog hole attacks intercept and record a signal in the analog domain, when it cannot be encryted. There is no way to prevent this attack. Speakers and headphones need analog signals. Even CRTs need to be driven from analog signals, through some fancy electronics is needed to convert the RGBHV back into something useable. Watermarking can make things harder, but not much.

Of course the Evil Empire doesn't seem to realise that. Over the years they have tried everything to protect their analog broadcasts and videos. The first recorded attempt to copy-protect an analog signal was a failed attempt to watermark records and radio broadcasts so casette decks would refuse to record. That attempt was a disaster. Manufacturers refused to make complient casette decks and lose sales. The watermark was audiable. The idea was rapidly abandoned. It was certinly not the end of analog protection through.

The first successful analog protection was probably Disney's Macrovision (now owned by Macrovision corporation). Macrovision was designed to protect rental tapes. The system worked well. Althrough electronics hobbyists quickly learnt how to build deprotectors Macrovision was quickly improved, until today. Macrovision has now been strengthed to the point is is causeing considerable compatability problems, and deprotectors are still available. More information is available below.

Althrough many companys are researching watermarks, success has been low. The analog hole is open and staying open :-). But analog protection still causes compatability problems, and can be annoying, so you should know about it anyway.

Macrovision	Moved.
Watermarking	The answer to the analog hole, or at least they will be if anyone every gets them working. A watermark (in theory) embeds a message into a signal which the viewer cannot see, but recorders can. Recorders seeing the watermark know its a copyrighted signal and wont record. An ideal watermark is robust, imperceptable and high-capacity. Actual watermarks are a case of pick-one. They can be seen or heard vith verying degrees of difficulty. They can be removed very easily. Unremoveable watermarks have been made but they make the signal unwatchable. Inperceptable watermarks have also been made, but they are very easy to remove. In between are watermarks which are both easily removed and easily seen. Audio watermarks are more successful than video watermarks. Some audio watermarks really are unaudible and still able to survive mp3 compression of d/a/d conversion. But they still dont last long against a deliberate attack. One semi-successful copy prevention system has used watermarks. The famous divx disc rental system watermarked the video signal. Viewers complained about the visible watermark, and it was still easily removed. Divx failed of course, but it was entirely economic. It couldn't compete with the better-marketed DVD. I have a collection of watermark-related files here. Some of the technical parts are very complicated.
CGMS	Moved.
Verance watermark	This is the audio watermark which will be used in DVD-audio and SDMI systems. Verance claims the watermark is robust, survives analog conversion and transmission and is unaffected by lossy compression. They also say the watermark has no effect on audio quality and the best "golden ear" quality judgers cant hear it. Sounds like their marketing departments overdoing things. No watermark can be that robust and still be inaudable. Verance has not released samples, so no independant assessments of the quality are available. I suspect an independant assessment would say it is very easy to hear. The watermark contains 72-bits of data comprising 4 CCI (copy control information) bits and 8 Usage Identifier bits every 15 seconds plus 60 Content Identifier bits every 30 seconds. Intrestingly, this watermark must survive both the obvious removal attacks and attempts to fake it. Some systems, such as SCMS, assume any analog inputs are infringeing. In future this watermark could be used to show otherwise, so the ability to fake a copy-freely mark could be very usful for more easeily exploiting the analog hole.
Camcorder Jamming	Moved.