You can generate keys like This open terminal, this only to generate a public key!
git clone https://github.com/Tiktodz/signed
git clone https://github.com/LineageOS/android_development development
bash signed/generate_key.sh
Then following this steps
If you have already pushed it to the repository, now is the time to do it. an example is just like this: 1 2 3
Remember that each ROM source has a different placement definition, it's better to always check the source first.
This is just a personal script, and is not mandatory for you to use..If you want to try it there's no harm in it, always generate a new key every time you build a different ROM because this is a public key.