A passage from Cory Doctorow's Little Brother that caught my attention was "[t]he problem had been that Turing was smarter than the guy who thought up Enigma. Any time you had a cipher, you were vulnerable to someone smarter than you coming up with a way of breaking it (99)." It first caught my attention because we just recently discussed World War II and Bletchley Park, where Alan Turing broke Enigma. Second, when Marcus, the main character of the novel, said "you were vulnerable to someone smarter than you coming up with a way of breaking it," I was reminded of the several in-class discussions about always assuming your cipher is breakable.
Throughout history, there have been several instances where cipher makers have been overconfident in the security of their ciphers. For example, in the 16th century, Mary Queen of Scots employed a substitution cipher, using numbers and symbols. Unfortunately for her, she placed too much confidence in both her cipher and her contacts, and by the use of frequency analysis, her cipher was broken, and her plot to escape imprisonment and murder Queen Elizabeth I was unveiled. In 1587, Mary Queen of Scots was executed.
Another example of cipher overconfidence came from the Germans during WWII. Their Enigma was incredibly secure, so naturally the Germans assumed that it was unbreakable. However, the British had a team of highly intelligent mathematicians on their side, including Alan Turing, who discovered a flaw in Enigma, and was therefore able to break it. He created a machine called a "bombe" that was able to break the daily German Enigma key. The Germans were unknowingly sending intercepted and decipherable messages. Their overconfidence in their cipher led to their ultimate downfall.
Overconfidence in one's security plays a large role in Little Brother. With the Department of Homeland Security monitoring nearly everything from transportation routes to Internet usage, Marcus and his friends were in serious need of ciphers and codes to protect their privacy. Marcus learns early on that with every bright idea, there exists another that is better. Most likely, there is always someone who's smarter.