Hi Sherief,
this is actually a complex problem. Thanks for trying to solve it.
With all due respect, I must say, what you are trying is just another hack to attempt to solve a problem at a higher level, which can not be solved at the level you are trying to solve it.
Some time ago, I wrote about it: [liberationtech] secure download tool - doesn't exist?!? https://mailman.stanford.edu/pipermail/liberationtech/2013-July/009620.html
See also my comments in Tor trac ticket 2340: https://trac.torproject.org/projects/tor/ticket/2340#comment:14
The whole approach of "you must download a verification tool or downloader to download what you really want to download" is something from an usability perspective, which only a small fraction of geeky users will do. I am sure, you can create something useful for a few people, I might even use it myself, but it's up to you if you want to solve it for the majority of users.
Do you speak C? If so, a solution which could work for more users, could be adding metalink + OpenPGP support to Firefox: https://bugzilla.mozilla.org/show_bug.cgi?id=331979
Then verification would work out of the box without installing other software.
If you agree with my points, I see two realistic ways to solve this. For one, solving the issue in Firefox. I am quite sure, Microsoft won't be helpful. Or ditch Firefox/Microsoft Windows at all and solve it in popular Linux distributions.
In case you are interested to solve the deeper issues, solving this is an interesting problem, which you could advocate. You could summarize the current problem why currently only a small fraction of downloaders uses verification, then do the draft work on how it could be solved (my comments in Tor trac ticket 2340), discuss it with Linux distributions how they would accept, then implement it and get Linux distributions to install it by default. The actual implementation could then also be done in python.
I'd do it myself, but I am already maintaining a Free Software project (Whonix), so I am happy that you showed up, interested to solve it.
Cheers, adrelanos