Idea: The ultimate CD/DVD auditing tool

[Tyler Durden]

As a basic idea it seems relatively workable. However, there's one detail 
that perhaps you might want to know about:

"We can push the idea a step further, making a stripped-down CD/DVD drive
that would be able basically just to follow the spiral track with its head
in constant linear velocity"


Unlike a vinyl record, the CD grooves don't form a spiral...they are 
concentric circles. Also, the beginning of the CD is towards the center, the 
end towards the edge.


-TD




>From: Thomas Shaddack <shaddack at ns.arachne.cz>
>To: cypherpunks <cypherpunks at lne.com>
>Subject: Idea: The ultimate CD/DVD auditing tool
>Date: Sun, 6 Jul 2003 04:13:32 +0200 (CEST)
>
>Pondering. Vast majority of the CD/DVD "protection" methods is based on
>various deviations from the standards, or more accurately, how such
>deviations are (or aren't) handled by the drive firmware.
>
>However, we can sidestep the firmware.
>
>The drive contains the moving part with the head assembly. There is an
>important output signal there: the raw analog signal bounced from the
>disk and amplified.
>
>We can tap it and connect it to a highspeed digital oscilloscope card. And
>sample obscene amount of data from it. In comparison with fast-enough
>ADCs, disk space is cheap. The problem can be in bandwidth, but for the
>drive speed set up to possible minimum (or for "normal" players) the
>contemporary machines should be sufficient. Real-time operating system
>(maybe RTOS-Linux) may be necessary.
>
>We get the record of the signal captured from the drive's head - raw, with
>everything - dirt, drop-outs, sector headers, ECC bits. The low-level
>format is fairly well documented; now we have to postprocess the signal.
>Conversion from analog to digital data and then from the CD representation
>to 8-bit-per-byte should be fairly straightforward (at least for someone
>skilled with digital signal processing). Now we can identify the
>individual sectors on the disc and extract them to a disc image file that
>we can handle later by normal means.
>
>We can push the idea a step further, making a stripped-down CD/DVD drive
>that would be able basically just to follow the spiral track with its head
>in constant linear velocity (easier to analyze than CAV) mode, with the
>ability to control the speed in accordance with how fast (and expensive)
>ADC, bus, and disks we have, and the possibility to interrupt/resume
>scanning anytimes in accordance with how much disk space we have (or to
>scan just a small area of the disc).
>
>As a welcomed side effect, not only we'd get a device for circumvention of
>just about any contemporary (and possibly a good deal of the future ones)
>optical media "protections", but we would also get a powerful tool for
>retrieving data from even very grossly damaged discs, for audit of
>behavior of CD/DVD writers and CD vendors (eg, if they don't attempt to
>sneak in something like a hidden serial number of the writer), and for
>access to all areas of the discs - including the eventual ones unreachable
>through the drive's own firmware.
>
>If we'd fill this idea with water, would it leak? Where? Why?

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