Apple and Amazon have filed patent applications which suggest that the firms are planning to offer secondhand marketplaces for digital content.

According to the US filings, each company is seeking to win claim to technologies which, if granted, would describe a marketplace where users can transfer their rights to digital content to another party or device.

In the filings, both companies describe how users could agree to transfer the digital rights management (DRM) protections on a piece of digital content to another user. Apple’s filing details how the transfer could take place, while Amazon’s describes the structure of a web-based store for digital content.

The described stores would turn the DRM holdings into a transferable commodity, allowing users to buy and sell “secondhand” content by acquiring the DRM from peers in the way users can buy and sell books and recordings in physical marketplaces.

Should the patents be granted and implemented, both companies could add used content services onto their respective online media stores.

Amazon offers both digital book and music content through its online markets, while Apple allows users to purchase digital books through the iBooks store and music and video content through the iTunes store service.

The launch of the services could also trigger a fresh round of legal turmoil for the companies should publishers and studios take exception to a model which could partially or fully cut them out of the revenue loop.

Apple is already in hot water with the US government over its iBooks service. Antitrust officials have argued that the company’s revenue model, which allows publishers to set their own prices, unfairly forces other retailers to adjust their own prices based on publisher demands.