which is the safest way to include a pair of key (public/private) in a apk

Question

I'm developing an application for android and I have to maintain a secure communication with a server through a pair of private and public key. Which is the safest way to storage the private key in my apk? Obviously I'm going to obfuscate the code but I want more security. I have thought the following option:

If I create a native share library with the methods for sign the transaction information, The apk only have to contain the .so file and this file is in machine code, so the decompilation could be difficult, isn't it?

any ideas? Thanks