Janus was the codename of a version of Windows Media DRM primarily for portable devices, whose marketing name was Windows Media DRM for Portable Devices (or in short form WMDRM-PD). It was introduced by Microsoft in 2004 for use on portable media devices which store and access content offline. Napster To Go was the first online music store to require the Janus technology. Supporting Janus often implies that the device also makes use of Media Transfer Protocol (MTP). Janus initially required supporting devices to not support non-Microsoft audio formats such as Ogg Vorbis, but this requirement was later removed.

Characteristics

To support Janus, devices must support: All of these are supported by way of challenge–response authentication commands.

Stores that required Janus on portable devices

Devices that used Janus