[FFmpeg-devel] Would a crypto file be acceptable?

[Mark Gaiser]

On Wed, Dec 21, 2022 at 4:44 PM Mark Gaiser <markg85 at gmail.com> wrote:

> Hi,
>
> The ffmpeg crypto protocol handler [1] allows one to play encrypted media.
>
> The great thing here is that it allows playback of any media format that
> ffmpeg supports!
> Have a container format like mkv as an encrypted blob, no problem for the
> crypto plugin!
>
> I'm explicitly mentioning mkv (though there's many more) here because that
> isn't possible in HLS/MPD. While those streaming formats handle encryption
> too, they are very limited in terms of supported codecs and containers.
>
> Playback of encrypted data works like this:
> ffplay encrypted_file -decryption_key $AES_KEY -decryption_iv $AES_IV
>

To amend, a more accurate example of how it currently works is this:
ffplay crypto://encrypted_file -decryption_key $AES_KEY -decryption_iv
$AES_IV


> While this works just fine, it's limited in use because the cryptography
> details have to be passed on the command line. Applications that might well
> support much of ffmpeg functionality can't easily hook into the crypto
> functionality. Take KODI for example, it allows playback of many of the
> formats ffmpeg supports but anything with crypto just isn't possible. In
> fact, anything that requires custom command line arguments isn't possible.
> [2]
>
> My idea is to make a new file format that would be implemented and specced
> within [1]. My proposed format would be:
>
> ---
> CRYPTO-VERSION:1
> CRYPTO-KEY:URI:.....
> CRYPTO-IV:URI:.....
> encrypted_file
> ---
>
> The URI would be a format type identifier where you can choose between URI
> (to pass a URL to a key blob), BASE64URL (key encoded as base64url) or HEX.
>
> The above proposed format should be stored in a file with ".crypto" as
> extension. The crypto plugin [1] would then handle that file. The arguments
> would be filled based on the "properties" in the file. So for example the
> `decryption_key` argument would be populated with the blob returned from
> CRYPTO-KEY:URI:<url>. Or with one of the other types.
>
> The "encrypted_file" would just be passed through ffmpeg's
> "ffurl_open_whitelist" like the crypto plugin currently does. Meaning that
> the file could be anything ffmpeg supports.
>
> Playing encrypted media would be as simple as:
> ffplay file.crypto
>

To amend this too.
The result should be no need to provide "crypto://". The ffmpeg file format
detection should detect that ".crypto" should be handled by the crypto
plugin.


>
> With this mail I'm looking for a confirmation if the above concept would
> be allowed as a patch for ffmpeg? And if not, how can I achieve the same
> results in a way that would be acceptable? [3]
>
> Best regards,
> Mark Gaiser
>
> [1] https://github.com/FFmpeg/FFmpeg/blob/master/libavformat/crypto.c
> [2] there are plugins to make it possible but then you have the extra
> requirement of a plugin
> []3 No, not HLS/MPD! They serve a different purpose. Extending them to
> serve my purpose is a lost goal to begin with so let's not even go there.
>