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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.

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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.

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