well for the file, the qt5-sqlcipher should do.
For being hacker proof, its very important you dont store anything
clearly in the exe file.
That goes for the variables too.
When u read into memory, make sure its not easy to locate
and read. ( in mem)
so do not store passwords or user names as clean text inside program.
all must be encrypted.
That will only keep noob hackers out.
Anyone pro, will most likely be able to get access if
unlimited access to app and data.