On Sunday 02 June 2002 08:24 pm, Joseph Ashwood wrote:
The MPAA has not asked that all ADCs be forced to comply, only that those in a position to be used for video/audio be controlled by a cop-chip. While the initial concept for this is certainly to bloat the ADC to include the watermark detection on chip, there are alternatives, and at least one that is much simpler to create, as well as more benficial for most involved (although not for the MPAA). Since I'm writing this in text I cannot supply a wonderful diagram, but I will attempt anyway. The idea looks somewhat like this:
analog source ------>ADC------>CopGate----->digital
Where the ADC is the same ADC that many of us have seen in undergrad electrical engineering, or any suitable replacement. The CopGate is the new part, and will not be normally as much of a commodity as the ADC. The purpose of the CopGate is to search for watermarks, and if found, disable the bus that the information is flowing across, this bus disabling is again something that is commonly seen in undergrad EE courses, the complexity is in the watermark detection itself.
The simplest design for the copgate looks somewhat like this (again bad diagram):
in----|---------------buffergates----out ----CopChip-----|
Where the buffer gates are simply standard buffer gates.
This overall design is beneficial for the manufacturer because the ADC does not require redesign, and may already include the buffergates. In the event that the buffer needs to be offchip the gate design is well understood and commodity parts are already available that are suitable. For the consumer there are two advantages to this design; 1) the device will be cheaper, 2) the CopChip can be disabled easily. In fact disabling the CopChip can be done by simply removing the chip itself, and tying the output bit to either PWR or GND. As an added bonus for manufacturing this leaves only a very small deviation in the production lines for inside and outside the US. This seems to be a reasonable way to design to fit the requirements, without allowing for software disablement (since it is purely hardware). Joe
Bzzzzztttt! Wrong Answer ! How do you prevent some hacker/pirate (digital rights freedom fighter) from disabling the "CopGate" (by either removing the CopChip, finding a way to bypass it, or figure out how to make it think it's in, "Government Snoop" mode ) ? Then the watermark can be removed. Remember it only requires ONE high-quality non-watermarked analog to digital copy to make it on the net and it's all over. -- Neil Johnson, N0SFH http://www.iowatelecom.net/~njohnsn http://www.njohnsn.com/ PGP key available on request.