[Gllug] [OT] CF card mp3 players?

[Mike Brodbelt]

On Thu, 2004-10-14 at 22:48, Richard Jones wrote:
> On Thu, Oct 14, 2004 at 10:51:28PM +0100, Russell Howe wrote:
> > http://encyclopedia.thefreedictionary.com/Secure+Digital
> > 
> > Note the bit about open source drivers being prohibited
> > 
> > Then I decided to check Wikipedia, to see if it had a better entry...
> > deja vu!
> > 
> > http://en.wikipedia.org/wiki/Secure_digital
> > 
> > I wonder who is copying whom...
> 
> Hmmm .. well Wikipedia is the original in case you hadn't guessed.  SD
> has some sort of digital restriction management (DRM), but how on
> earth this is supposed to work given that it presents a pure /dev
> device to Linux I have no idea ...

SD presents a superset of the functionality of MMC. An MMC card
basically contains addressable memory and a memory controller chip,
IIRR, and most readers just present a USB mass storage interface to the
host. SD is the same, with one addition - it also has a "protected"
region for holding keys, which can be used to lock content to devices
containing the correct keys.

As far as I understand/remember, SD implements the SDMI specifcation of
CPRM. So, if you download an mp3 track using say, a mobile phone, the
track will be encrypted, and a device-locked key stored in the protected
region. This effectively locks the track to the original device, as only
that has the correspondong key to get at the key needed to decrypt the
data.

In practice, this means that open source drivers for SD card readers and
similar devices are no problem - the only bit that requires the closed
source spec is the DRM stuff, and there's not many reasons to want to
use that anyway. The same kind of thing is present in MagicGate memory
sticks as well. I have a USB Sandisk SD/MMC reader that works just fine
under Linux, both for my MMC cards, and my 256Mb SD card, which I use
mostly with my PalmPilot.

Mike.

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