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In Telegram messenger, latest update, there is an option to set connection type to MTProto Proxy.

Note: There is a detailed description by Telegram team on MTProto.

Now telegram officially announced that the Data encrypted in MTProto Proxy can not be deciphered by any third party due to the usage of end-to-end encryption.

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Logically, Is it possible to implement a method that proxy server is not able to interpret passing data to Telegram Server at all?

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Logically, Is it possible to implement a method that proxy server is not able to interpret passing data to Telegram Server at all?

That's not specific to Telegram. If you are using a HTTP or SOCKS proxy to visit site with HTTPS you still have end-to-end encryption, i.e. the proxy sees only encrypted traffic. It is different when having a SSL intercepting proxy which one usually finds in companies but also as local proxy in antivirus products. In this case the proxy will decrypt end re-encrypt the traffic in order to analyze it. But this would also mean that your client is explicitly trusting the proxy to do this, see Does https prevent man in the middle attacks by proxy server? for more details about SSL interception.

But even if an SSL intercepting proxy is used it would still be possible to add yet another level of end-to-end encryption on top of it with fixed information of what kind of end-system is expected, i.e. similar to certificate pinning. Even an SSL intercepting proxy will only see the encrypted traffic and might decide to pass it or block it but will not be able to look further into it.

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