I made a key mold out of a 2 part chemical mix. I have a lot of this lying around because I had a friend who had a lot of miniatures and he let me make molds of them. It works like a normal mold. You poor your material through the opening at the "top", let it cool, open it up, and remove your key.
I made it In school using as a school project the steps shown in the instruct able file. We were told to use the materials we had to "make something". I worked alone, as the project required.
I made it in my schools engineering department. I chose this because I have made several molds before and I was confident that it would get me an A on the project.
My biggest challenge was suspending the key in the mold wile it was drying. I usually do this with play dough but i forgot to bring that to school so I had to make do with what i had. If i were to do this again i would remember the play dough and probably have the poor hole on the side of the altoids tin instead of on top.