Thread by @doctorow

With the world in lockdown, most "white-collar" crime (AKA "world-destroying corruption and looting") now takes place over Zoom. If you witness such a crime, you might be tempted to record the meeting and leak it to a journalist.

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But leaking Zoom recordings is seriously fraught because they are full of personally identifying details. Some of these are "traitor-tracing" mechanisms, others are intrinsic to Zoom, and still others come from your end of the recording.

theintercept.com/2021/01/18/lea…

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Nikita Mazurov's guide to anonymizing Zoom videos for @theintercept tackles each of these classes of identifiers.

Traitor-tracing: Zoom meeting hosts have the option to add visual and audio watermarks to their videos.

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The visual ones are perceptible - displaying your name/email on the screen so that it will be present in any video-grab - but the audio watermarks are a series of ultrasound chirps with unique identifiers in them.

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It's not clear where the audio watermark is inserted; Marzurov hypothesizes that the ultrasonic watermarks are inserted by your copy of the Zoom client, so using an external recording tool might bypass them.

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Another important identifier in Zoom recordings is the arrangement of the other participants; this is different for every viewer.

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Any recording will reveal information that could identify the leaker: not just the user's OS, but also pop-up alerts about emails and messages.

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Source protection with Zoom captures is really hard - but that's all the more reason for this discussion to take place in earnest.

eof/