The Box.net repository enables users to copy files from Box.net into Moodle.
Enabling the Box.net repository
The Box.net repository may be enabled by a site administrator in Settings > Site administration > Modules > Repositories > Manage repositories.
Obtaining an API key
Create a Box.net account at http://www.box.net/.
Visit http://www.box.net/developers/api. Click on Start developing, then Create new application, fill out the form and 'Save service' to get your API key. For all the settings, Moodle doesn't care what you put in.