GAMFT has the capability of running local commands. Utilizing that functionality, you can take a file that has been uploaded or currently exists and pass that into the local command to generate the MD5 or SHA1 hash of the file, returning that value to the GAMFT Workflow.
Now, it's just a matter of doing comparisons against your specified named list. Search a Table, CSV, XML, etc... compare against value generated and you have your conditions identified.
Named list cleanup can be done separately.
You could also create a custom task that does this for you as well. Pass the file name into the custom task and it returns the SHA1 value for you.
Either way, you have the information you need for processing.