Zip file to verify if not modified

I want to zip source code of my application and provide it to my client. I want to somehow assign to it an id or whatever which would describe the status of zipped files in official agreement between me and my client. I am not sure but i think there is something called checksum. Is that checksum something that will not change until someone would change anything inside the zip package? Therefore once files are zipped can i use such checksum id and put it into my agreement with customer or? If that’s the case what should i do once i zipp the files and how to get such id? Thanks in advance for your support.