to read the whole project is a big task.
Is there any open-source, simple project which just for implement the signing function. It must be open source, no one will trust this kind of software, even Electrum .if I want to sign a message with more than 100 bitcoins, I really can not trust any software even with big companies. Do you think so?
I couldn't find any simple PHP code that can sign/verify the message.
The open-sourced that I provided above is owned by
fbueller who develop bit-wasp. He is no longer active since 2017.
If you can't trust that source why not run this offline?
Or do you want to run this on your website? If yes then you need to study his code to make sure the codes are safe.