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 client then uses the K content as an RC4 key to decrypt the licensed media stream.Īs 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:Īn 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. The server also sends a content key ID, unencrypted. The server encrypts the key before transferring it to the client with a globally predefined 160-bit ECC key, ECC 1.
According to the specification, the client software obtains a 7 byte plain-text content key K content from the license server.
In May 2007 Microsoft published the network protocol behind its license acquisition mechanism.
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