Quote:
Originally Posted by pdurrant
Oddly enough, both Amazon and Kobo have per-book encryption keys. Amazon's scheme is based off a device-level key, so isn't exactly what you describe, but Kobo's scheme is precisely one key per book, key provided to the Kobo desktop reading software over the internet.
But all the keys must be stored by the reading software, to allow off-line reading. So it's just a question of getting access to the app's key store and reverse engineering the encryption scheme. [software name deleted]
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Okay, if the keys are in persistent storage, that makes it easier for now. However, that can change. In my job, I'm working with Trusted Execution Environments that allow stuff to be encrypted and decrypted on the device without the keys being accessible within the main OS, and the environment is becoming more widely available in systems with ARM CPUs. Using the TEE to encrypt the key store would make it hard to crack. You'll probably be back to trying to fish the key out of the app when it has the ebook open (assuming that they don't keep the key in the TEE and do all decryption inside it).
I hope I'm not giving the impression that I'm for DRM encryption; I despise it for various reasons. However, I'm afraid that the attitude that DRM encryption is nothing to worry about because we'll _always_ be able to circumvent it easily is wrong.