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+# Widevine L3 Decryptor

+[Widevine](https://www.widevine.com/solutions/widevine-drm) is a Google-Owned DRM system that's in use by many popular streaming services (Netflix, Spotify, ...) to protect media contnet from being downloaded.

+

+But Widevine's least secure security level, L3, as used in most browsers and PCs, is implemented 100% in software (i.e no hardware TEEs), thereby making it reversible and bypassable.

+

+This Chrome extension demonstates how it's possible to bypass Widevine DRM by hijacking calls to the browser's [Encrypted Media Extensions (EME)](https://www.html5rocks.com/en/tutorials/eme/basics/) and decrypting all Widevine content keys transferred - effectively turning it into a clearkey DRM.

+

+## Usage

+To see this concept in action, just load the extnesion in developer mode and browse to any website that plays Widevine-protected content, such as https://bitmovin.com/demos/drm.

+

+Keys will be logged in plaintext to the javascript console:

+

+`WidevineDecryptor: Found key: 100b6c20940f779a4589152b57d2dacb (KID=eb676abbcb345e96bbcf616630f1a3da)

+`

+

+Decrypting the media itself is then just a matter of using a tool that can decrypt MPEG-CENC streams, like `ffmpeg`. e.g:

+

+`ffmpeg -decryption_key 100b6c20940f779a4589152b57d2dacb -i encrypted_media.mp4 -codec copy decrypted_media.mp4`

+

+## How

+In the context of browsers the actual decryption of the media is usually done inside a proprietary binary (`widevinecdm.dll`, known as the Content Decryption Module or CDM) only after receiving the license from a license server with an encrypted key in it.

+

+This binary is usually heavily obfuscated and makes use of third-party solutions that claim to offer software "protection" such as [Arxan](https://digital.ai/application-protection) or [Whitecryption](https://www.intertrust.com/products/application-shielding/).

+

+Some reversing job on that binary can then be done to extract the secret keys and mimic the key decryption algorithm from the license response.

+

+## Why

+This PoC was done to further show that code obfuscation, anti-debugging tricks, whitebox cryptography algorithms and other methods of security-by-obscurity will eventually by defeated anyway, and are, in a way, pointless.

+

+## Legal Desclaimer

+This is for educational purposes only. Downloading copyrighted matirials from streaming services may violate their Terms Of Service. Use at your own risk.

+