33 lines
2.4 KiB
Markdown
33 lines
2.4 KiB
Markdown
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# Widevine L3 Decryptor
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[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.
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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.
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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.
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## Usage
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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.
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Keys will be logged in plaintext to the javascript console:
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`WidevineDecryptor: Found key: 100b6c20940f779a4589152b57d2dacb (KID=eb676abbcb345e96bbcf616630f1a3da)
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`
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Decrypting the media itself is then just a matter of using a tool that can decrypt MPEG-CENC streams, like `ffmpeg`. e.g:
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`ffmpeg -decryption_key 100b6c20940f779a4589152b57d2dacb -i encrypted_media.mp4 -codec copy decrypted_media.mp4`
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## How
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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.
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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/).
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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.
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## Why
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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.
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## Legal Desclaimer
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This is for educational purposes only. Downloading copyrighted matirials from streaming services may violate their Terms Of Service. Use at your own risk.
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