https://news.ycombinator.com/item?id=12089993 … < On WhatsApp not working in Saudi. Calls are filtered by firewall, so the UI just blocks them rather than timeout.
Suppose as an example the call were mp3 streams. Encode the ciphertext as quantized DCT coeffs in valid mp3 streams.
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Now you need audio analysis (moderately expensive for firewall) to determine if the call is encrypted.
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you can block any audio stream which are not known protocol. If I understand you correctly, you pay a lot BW for stegn
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Steganography to fool humans or smart analysis tools costs a lot in BW. OTOH what I described is just a few % BW cost.
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then I don't understand why can't you sample the mp3 and block ones with high entropy in DCT coeff
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Roughly the same reason gzipping an mp3 doesn't get you much.
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Of course more advanced analysis is possible, but there are development and runtime costs, hopefully high.
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I don't claim this is a fully-developed solution, just a possible framework for how it could be done.
End of conversation
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