PHP: Download files stored in SQLite (BLOB)

I need help with this:

On my server, I have a SQLite3 database with several files and a PHP (5.2) download page. In the DB, files are stored in a table with SHA1 (TEXT) and the File (BLOB).

The URL is like this: http://ift.tt/1MQcP9R...

The idea is: when a user go to a download url and submit the SHA1, the PHP script read the associated DB entry (the BLOB with binary data) and start the download.

I'm quite noob to PHP, so I don't have any idea of how to make this. I tried to find how to make this in Google without result. Additionaly, my english level is bad, sorry if this is mistranslated.

Thanks in advanced.