The "safe" looks like Windows Calculator.
A code is entered with numeric keys. A code opens an Explorer-like window to select files for "storage".
OR, files can be dragged & dropped onto/into the safe. Another code shows what files are being stored, and yet another opens a window from which stored files can be clicked on and dragged onto desktop for retrieval.
There is a very old version of such a product around not nearly as comprehensive as what i described. The safe need NOT be windows Calculator, any other benign windows accessory can be used. Calculator lends itself well for the obvious input method.
this is a product I plan to use with friends to keep files safe/private. I might want to sell the product or offer it as freeware initially.