Warp wrote:

>   For example the PlayStation Portable supports running programs from
> the flash memory card directly (instead of the optical disc), but only
> ones approved by Sony. It will refuse to run anything else.
>   Of course in order to run them it needs to decrypt them, and to decrypt
> them it needs a decryption key. Couldn't this key just be read from the
> PSP's memory and use to encrypt third-party programs? The answer is: No.
> The decryption key can be read, but it cannot be used to encrypt the
> programs.

Asymmetric encryption. I can see how that would work. (OTOH, couldn't 
you just modify the firmware to not require this?)

>   Of course in the case of music you don't need any encryption key, as
> the decryption key is enough to do what you want. The only way to protect
> that is to protect the decryption key and the decryption process in such
> way that you can't get hold of it. Basically you would need a black box,
> which is the music player, which cannot be looked inside. That's, in fact,
> what the music industry is aiming towards, even if this "black box" is
> inside the user's PC or handheld device.

I see two possibilities.

1. There is one secret decryption key. Every iPod (or whatever) has this 
key burned inside it, with tamper-proof hardware to stop you getting at 
it. In this case, you don't *need* to decrypt the data; you can just 
copy the encrypted files and they will play perfectly on any iPod. So 
this is clearly a non-solution.

2. There is a unique key inside every iPod. That means that music which 
you have legally purchased can only ever be played on 1 device. So this 
is clearly also a non-solution.

I'm not seeing a way this can be made to work properly...

-- 
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*

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