Patent ID: 7818811

Claim:
A method comprising: authenticating off-line each other between a first user and a second user; checking off-line whether the second user has a valid account with a service provider; negotiating freely off-line a price via an off-line sales transaction for a secure off-line transfer of a digital media content from a first media playback device of the first user to a second media playback device of the second user, wherein the off-line sales transaction comprises: receiving a cryptographically secure purchase request from the buyer; verifying the cryptographically secure purchase request using a public key of the buyer; sending a cryptographically secure transaction receipt to the buyer who verifies the cryptographically secure transaction receipt using a public key of the seller; and receiving a receipt acknowledgement from the buyer, wherein the receiving completes the sales transaction; securely storing off-line a proof of the off-line sales transaction between the first user and the second user in both of the first media playback device and the second media playback device, wherein the second user can enjoy the digital media content off-line without limitations and without paying the price right after the off-line sales transaction; providing a first percentage of the price, by the first user, to an owner of a copyright of the digital media content based on the proof stored in either the first media playback device or the second media playback device; and receiving a second percentage of the price by the first user based on the stored proof, wherein the off-line authentication, the off-line checking, the off-line negotiating, and the secure off-line storing comprising a peer-to-peer link involving no communication link to the world outside of the first media playback device and the second media playback device.