What happens when I include parts of code(maybe logic/algo, design approach and change its implementation or implement it in a different programming language) of an open-source copy left software in my software and try to make it proprietary? So how will proprietary license issuing authorities verify authenticity of my software(code)? I will claim it as my original work and will never acknowledge that I built it by referencing an open-source work.
What “proprietary license issuing authorities”? There is no such thing.
You sell your software for money with a proprietary license. Someone suspects you copied someone else’s code and tells the copyright holder. The copyright holder can be nice and ask you to stop selling under a proprietary license, tell all your customers that your software is under an open source license, and/or pay them money.
Or they take you straight to court. You will be forced to show the evidence (your source code) to their lawyers, they will find the evidence, and sue you for the maximum damages.
BTW Making false claims in court is a serious crime, like lying that you never copied any one’s code.