Private or public key. Which should I use for DFU secure bootloader

SDK17.0.2 example dfu\secure\bootloader

in the dfu_public_key.c it say's that "This file was generated with a throwaway private key, that is only inteded for a debug version of the DFU project."

and "Please see github.com/.../README.md to generate a valid public key."

and "/** @brief Public key used to verify DFU images */"

It seems a bit confusing to me since 'This file was generated with a throwaway private key.' and then '/** @brief Public key used to verify DFU images */'

I assume I am supposed to create a public key but I would like to be sure.

So, my questions are:

1, Should I create a private or public key?

2, What is the difference between a private and a public key?

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