This Doesn't look like a exact replica, but it does release and serves the purpose of a hidden blade, every gamer that plays Assassin's Creed should make one...
This is my first tutorial.
Check it out in action on Youtube: https://www.youtube.com/watch?v=OHSBf6c1E6I

Step 1: Materials

Here are the materials that you will need:
1. Altoids Can
2. Blade
3. Wire (1 and 1/2 foot to be safe)
4. Aluminum Foil
5. Zip-Ties or Wire
6. Strap or Cut Belt ( Better if adjustable)
7. Drill
8. Knife
9. Binder Clip
10. Spray Paint (optional)
11. Electrical Tape (optional)
12.Screwdriver (optional)

Step 2: Step 1. Altoids Tin

I am using the completed version for pictures, which I spray painted black.
Step 1. You will need to cut a hole for the blade, and the wire that is used to deploy the blade.
The way that I made the hole for the blade is as follows, i pushed the blade through the Altoids Tin from the inside.
The reason you want to push it from the inside is because it makes for a smoother deploy
The way that I put a hole for the wire ( located right under the blade hole) is as follows, I put a Phillips head bit on a drill and I pushed the drill onto the Altoids Tin and after a few seconds you have a smooth hole for the wire to run through.

Step 3: Blade

Step 2. The next step is dealing with the actual blade itself.
You will have to attach the wire to the back of the blade
I recommend that you wrap the wire around the blade a few times and finish it off with electrical tape.
Be aware that you have to put the wire on the right side, which can be determined by how you made the hole with the blade.
After you have connected the wire to the blade, and wrapped it in electrical tape, put the binder clip on the back of it

Step 4: Lid With Arm Mount

Step 3. You will have to drill two holes parallel to each other as shown in the picture
I recommend using the drill for the holes
When the holes are drilled use a zip-tie to hold the belt or strap down
I used a wire.
If that doesn't hold well I would reccommend using one or two pieces of electrical tape to help hold it down.

Step 5: Assembly

Step 4. in this step we will assemble the inner workings of the blade.
I recommend that you fold up some aluminum foil and place it on the bottom till the blade can lie flush with the blade hole
After you insert the foil you should but the blade in the blade hole and run the wire out its hole
Put on the lid, Attach it on your arm and your middle finger and blade away.