Windows Media DRM or WMDRM, is a Digital Rights Management service for the Windows Media platform. It is designed to provide delivery of audio or video content over an IP network to a PC or other playback device in such a way that the distributor can control how that content is used. WMDRM includes the following components: Windows Media Rights Manager (WMRM) SDK for packaging content and issuing licenses Windows Media Format SDK (WMF SDK) for building Windows applications which support DRM and the Windows Media format Windows Media DRM for Portable Devices (WMDRM-PD) for supporting offline playback on portable devices (Janus) Windows Media DRM for Network Devices (WMDRM-ND) for streaming protected content to devices attached to a home network (Cardea) Windows Media DRM was replaced in Windows 10 Anniversary Update in favor of Microsoft PlayReady. How it works In May 2007 Microsoft published the network protocol behind its license acquisition mechanism. According to the specification, the client software obtains a 7 byte plain-text content key Kcontent from the license server. The server encrypts the key before transferring it to the client with a globally predefined 160-bit ECC key, ECC1. The server also sends a content key ID, unencrypted. The client then uses the Kcontent as an RC4 key to decrypt the licensed media stream. As an anti-spoofing measure, additional fields such as playback rights and a random number are encrypted with three more predefined ECC key pairs either by the client or server software: client software ECC key pair KC, client machine ECC key pair KM, server software ECC key pair KS. An analysis of version 2 of the DRM scheme in Windows Media Audio revealed that it was using a combination of elliptic curve cryptography key exchange, the DES block cipher, a custom block cipher dubbed MultiSwap (for MACs only), the RC4 stream cipher, and the SHA-1 hashing function. Windows Media DRM is designed to be renewable, that is, it is designed on the assumption that it will be cracked and must be constantly updated by Microsoft. The result is that while the scheme has been cracked several times, it has usually not remained cracked for long. Version 1 was released in April 1999 and supported basic business rules such as expiration dates. Version 2 was released in January 2003 and is also known as version 7.x and 9, to keep in sync with the equivalent versions of