Password protect binary files on database.

Hi! I am currently working on a project that involves uploading binary files onto a MySQL database(know that I should be avoiding this, but is is one of the requirements of the project). The binary files then need to be downloaded. Uploading and downloading the files, is not a problem. Now, the problem is that I need to "password protect" this files on the database before downloading. Does anyone know if this if possible, and if it is, point me in the right direction? Thanks Renato