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Comment by lifty | Hacker News Reader

Regardless of e2ee, they might have code bundled in the WhatsApp app that just deletes local video messages based on a hash. That wouldn’t break encryption.

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Same message doesn't mean same hash. Usually a nonce is used and if not: WhatsApp uses the Signal Protocol, which uses different keys for each message

The client can delete the message if the decrypted hash matches a certain blacklist. It doesn't have to happen on the FB servers.

Such a mechanism allows governments to turn WhatsApp into a propaganda machine very easily, though, so I'm not sure if I would consider such a mechanism for my app if I were in a similar position.

You cannot and should not be able to use a hash or rainbow table for encrypted messages. If that is possible (you don't use a nonce), then your encryption is broken since many common messages can be looked up in a rainbow table and you can use replay attacks.

That would have to happen on the device before encryption or after decryption.

Whatapp's client applications already do this before encryption to check against a list of hashes of child abuse material.

This is of course great, but such hash based filters for images or videos can be circumvented easily by just flipping one bit (without corrupting the file). I guess what we really need is some kind of ML trained filter that has a great rate of success and a very low false positive rate.

It was an event link, think:

  > The event next week:
  > https://....

(Neither of us remember if those two lines were distinct messages or two lines in the same message; regardless, neither is there anymore)

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