[Taylor514ce]

In several of the DRM / Piracy threads, I've mentioned the idea of using Public Key Cryptography as a system for allowing unlimited personal use of purchased media without shackling that use to a particular format or device.

The result has been a resounding brief silence, and then the resumption of the thread with ideas like watermarking or embedded chid-porn tracking viruses... umm, ok... what's wrong with using a system that already works?

I'm no expert, but the central idea behind public key cryptography is that your key comes in two parts, a public part you share, and a private part you keep private. It's just a big number, so

Core Concept #1: You can store your key anywhere you like, such as on an SD card or USB device.

To purchase a book, the book seller would encrypt your personal copy of your book with your PUBLIC key, which you can "give" them as part of the transaction. This could be completely automated. To read the book, decrypt it with your private key. Again, all this can be automated, and has been, in several systems (email, https, WiFi, etc.)

Core Concept #2: Nothing in this scheme ties you to a specific device.

What if I lose my key? Most key's are generated via a seed value, such as a simple password. For example WEP encryption on WiFi routers use a seed value. That's why you can have several different computers on your home WiFi network, but exclude all of your neighbors. If you lose your key, you can regenerate it (usually).

This seems like a perfect way to sell individual, unique copies of books, without limiting the buyer to specific devices or number of devices.

Keep your library of encrypted books anywhere you like, on a PC, on an SD card, on an e-book reader. Keep your key on an SD card. Combine the two, read your books.

What am I missing?