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I recently flew with United Airlines and I used their free messaging wi-fi plan.

I could text my friends on Whatsapp, but I could not send (nor receive) multimedia content like images, videos or audio clips.

I'm wondering how this works and whether it is secure. Since they're able to selectively block traffic, I'm assuming that this blocking goes beyond a simple white-listing. Somehow they managed to inspect my traffic and block byte-heavy content.

As far as I know Whatsapp has end-to-end encryption, so honestly I'm at my wits' end regarding how this works. Would they be able to read my texts? My online searches haven't helped so far.

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  • WhatsApp probably sends images over different ports than text messages. Breaking the encryption is almost impossible
    – UndercoverDog
    Aug 18, 2022 at 14:54
  • Relevant: security.stackexchange.com/questions/254736/…
    – schroeder ♦
    Aug 18, 2022 at 15:08
  • Size of text message is smaller than chunks of multimedia. They can block those packets that are larger than the average size of text messages. On whatsapp, this will timeout the upload and will prompt you to retry.
    – defalt
    Aug 18, 2022 at 15:11
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    They don't need to see the content of the traffic to be able to see the size of the traffic.
    – schroeder ♦
    Aug 18, 2022 at 15:13
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    I think what you need to google is "whatsapp block attachments" and you will find out how it is done. There are tons of references to how this is done.
    – schroeder ♦
    Aug 18, 2022 at 15:14

1 Answer 1

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Whatsapp uses different servers to process attachments. They are hosted on different domains. All they need to do is to block those multi-media processing domains.

Reference: paper 2015

These types of filters are available pre-configured on some firewalls and URL filtering services.

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