How to protect your C++ application from internet packet sniffer?

Question

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Good time of the day!
The question is in the header :)
I have an application that interacts with php scripts on my domain, and the entrance there contains several levels of protection (a special pattern of user agents, requiring authorization before entering the api and checking the unique computer identifier), what other ways can there be to protect from the entrance of an outside user?

Answer 1

Protect for what and from what?
There is no way to prevent packet sniffing.
Prevent access to content - you can if you use content encryption.
And the filter by user agent practically does not affect anything, since changing it is not a problem at all.