There is nothing like market key password or any types of password to control whole stock market (There can be password for individual traders). Haven't watched the movie you have mentioned above and i don't think i will watch it in future. Its just a script made by some random guy who don't have any idea about how stock market works.
Probably that is just an entertainment which might not be dealing with practical security measurements of exchanges. Moreover I am understanding this idea like they might be imagining an exchange system similar to bank lockers and all the funds are being protected with only one key which is not at all existing with respect to modern security measurements.
I am quite surprised to see 7.5/10.0 rating they got.
IMDB ratings are not for logical things, it is for how good the movie in entertainment scale. Moreover it is user driven rating might have been bumped by paid reviews too (just to have some good fame).