wm-drm on linux

schneidz · 07-10-2007, 01:18 PM

this is more a question of how drm works...

but if you have a (legally obtained) kid/sid pair in a text file, would one be able to decrypt the .wmv by x-or-ing the kid and/ or sid against all the bytes in the .wmv file ?

basically i would like to program a player that will use a legally obtained key to decrypt a drm'ed wmv.

how would i find information on how windows media player does it ? (i.e.- does it circular shift bits, x-or bytes, add ff to each byte...)

let me know what you think.

thanks,

kummiliim · 07-11-2007, 06:31 AM

"The ASF container provides the framework for digital rights management in Windows Media Audio and Windows Media Video. An analysis of an older scheme used in WMA reveals that it is using a combination of elliptic curve cryptography key exchange, DES block cipher, a custom block cipher, RC4 stream cipher and the SHA-1 hashing function."
http://en.wikipedia.org/wiki/Advanced_Systems_Format

Not going to be easy : D, best of luck. I'm not sure but hasn't that already been done?

schneidz · 07-12-2007, 03:28 PM

the only thing i know of that does this is windows media player in windows. that is partially how i got the key into a text file.

i know that xine, mplayer, ... dont have the ability to ask a webserver for a certificate but if it already had one i figured it would be trivial to program how to use it when spitting out bytes from a stream.

i guess i was thinking too ambitiousely.

thanks,

sundialsvcs · 07-12-2007, 10:09 PM

Nevermind. DRM is a dead dodo. It just hasn't fallen over yet. But it will soon.

jschiwal · 07-12-2007, 10:24 PM

Quote:

basically i would like to program a player that will use a legally obtained key to decrypt a drm'ed wmv.

Even you purchased the key, even talking about how to use it (as if I knew) might be illegal. The MS way of doing things is for you to use their magic sdk. Without studing their patent, or being an encryption expert, you probably will have a hard time.

kummiliim · 07-13-2007, 08:52 AM

Things like this make me glad I still live outside DMCA.