Tapani Saarinen
Guest
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 Posted:
Wed Sep 28, 2005 12:30 am Post subject:
Newbie questions |
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I'm new to WMA DRM. Could someone please answer the following questions:
1. Is the WMA file encryption key device/user spesific or is it possible
to superdistribute the WMA file and acquire license (rights object) in
each device without downloading the content again?
2. If the WMA file is encrypted using device/user independent key and
the key is delivered inside the license, how is it ensured that someone
does not distribute the decryption key to all his friends? If the
license owner has the decryption key with right software he can decrypt
the content and convert it to MP3, right?
3. How does Windows Media Player acquire the license? Does it open some
web page where the user makes the purchase and downloads the license?
What about the mobile Media Player, does it open a web browser or what?
Is it possible to use some mobile application for the purchase instead
of the web browser?
4. Can I start encrypting and selling WMA files if I have the MS Media
DRM SDK and a way to bill credit cards or do I need some certificate or
something like that from Microsoft before I can encrypt the files or
create licenses?
Br,
Tapani
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Greg Rubin
Guest
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Wed Oct 19, 2005 12:30 am Post subject:
Re: Newbie questions |
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"Tapani Saarinen" <tsaari@r_emove.nic.fi> wrote in message
news:4339b650$0$27911$7b1e8fa0@news.nbl.fi...
| Quote: | I'm new to WMA DRM. Could someone please answer the following questions:
1. Is the WMA file encryption key device/user spesific or is it possible
to superdistribute the WMA file and acquire license (rights object) in
each device without downloading the content again?
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Yes. You only need to package (encrypt) the file once. You can then give
it out to as many people as you want.
| Quote: | 2. If the WMA file is encrypted using device/user independent key and
the key is delivered inside the license, how is it ensured that someone
does not distribute the decryption key to all his friends? If the
license owner has the decryption key with right software he can decrypt
the content and convert it to MP3, right?
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You've latched onto the fundemental weakness of all DRM systems. There user
of the information is not trusted. What happens here (roughly) is that
every Windows box has a unique key. When you give Alice a license, it
contains the key to the media file encrypted by Alice's Computer's key.
Thus, if Eve somehow gets a copy of Alice's license, it is useless because
she doesn't have the key associated with Alice's machine. The computer key
is carefully protected by the OS. So is the content key during the brief
period of time that it's decrypted so that it can be used to decrypt the
media.
I don't know about the final question, but I do know that MS works as hard
as they can to prevent that. As to they're level of success? I don't know.
| Quote: | 3. How does Windows Media Player acquire the license? Does it open some
web page where the user makes the purchase and downloads the license?
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Implicitly, yes. Each packaged media file contains a URL which the media
player will access and ask (via encrypted POST parameters) for a license.
The page returned can either by the license, in which case the content
simply plays and the user barely notices that anything has happened (This is
called "silent delivery" and generally is a better user-experience.), or the
page could be a valid HTML page which the media player will display in an
embedded IE window. You can manage logins/purchases/business logic here and
then deliver a license at the end.
| Quote: | What about the mobile Media Player, does it open a web browser or what?
Is it possible to use some mobile application for the purchase instead
of the web browser?
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I don't know.
| Quote: | 4. Can I start encrypting and selling WMA files if I have the MS Media
DRM SDK and a way to bill credit cards or do I need some certificate or
something like that from Microsoft before I can encrypt the files or
create licenses?
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IANAL, sorry.
Greg |
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