Code cracking is often handled unrealistically in movies and TV shows. Make your games more realistic by having codes be completely unguessable and uncrackable - without social engineering to obtain the codes from someone who knows them, by stealth or deception.

Well, unless you're running a game in a school and people are using the pigpen cipher.

Transcript

Luke: You just made up a code! That's not how codes work!
Han: It'll work. It'll work.
{cut to Jhoff}
Jhoff: Check it out, Admiral. These buffoons are in the stolen shuttle.
Admiral Piett: Interesting fact: The odds against guessing the correct code are 78,364,164,095 to 1.
Jhoff: Never tell me the odds again. They got it wrong, anyway.
Darth Vader: Where is that shuttle going?
Admiral Piett: They want to go to the Peace Moon. I was going to blow them to kingdom come.
Darth Vader: Make it so.
{cut to Luke on the shuttle}
Darth Vader: No. Wait... Give them a trajectory and landing clearance. I shall deal with them.
{cut to shuttle}
Jhoff: {over radio} Shuttle Tydirium, transmitting flight path.
{cut to Jhoff}
Han: {over radio} Yeah! They fell for it. Suckers!