Learning #6: Infinite Monkey Theorem

Hello, I am back! Yes, I know what you are thinking. It was been many days since I last blogged and if you do some simple math, you have now come to the realization that it is impossible for me to blog everyday given that I have missed a couple days.

Not making any excuses, but I got a bit backed up on work and a bit overwhelmed – the learning curve hit me pretty hard. And then imposter syndrome hit. Do I belong here? The usual new job, new challenge excitement. I am sure most people have been there, done that. First week in a nutshell:

hit hard

But, I survived the first week and now I am back rocking and rolling!

Yo Adrian!

^ me calling to all my blog readers (substitue Adrian for your name)

And in these coming weeks I am hoping to stay in tune with what I believe is a good plan for accomplishing my goals this summer:

Will take some focus in the upcoming weeks and some serious commitment to training for both work and track:

Rocky Training

Back to the Usual Content

But enough blabering about my rocky week (pun intended). Y’all came here because you either clicked on the wrong link, stalked my GitHub profile, or interested in learning about some cool stuff.

Infinite Monkey Theorem

In doing basic research for my first task at the Stellar Development Foundation on Tuesday, I came across the Infinite Monkey Theorem. The theorem states:

“a monkey hitting keys at random on a typewriter keyboard for an infinite amount of time will almost surely type any given text, such as the complete works of William Shakespeare”Wikipedia.

Believe it or not, this theorem is very much real and even has a nice mathematical proof.


Consider the word banana. The odds that a single monkey types the word banana is, given a keyboard with 50 keys is 1/50. Thus, the odds of a monkey typing, at random, the word banana on the first try is (1/50) x (1/50) x (1/50) x (1/50) x (1/50) x (1/50) = 1/15,625,000,000 since these are all indepedent events. Consider then the odds that the monkey does not type teh word banana on its first try: 1 - 1/15,625,000,000. So, we get that the odds of a monkey not typing banana on its first try to be 0.999999999936. Consider a zoo of ten monkeys. If the zoo sat these ten monkeys down at ten desks and had them indepdently type six characters, the odds that none of the monkeys typed banana is:

0.999999999936 + ... + 0.999999999936 = (1 - (50 ^ 6)) ^ 10
                                      = 0.9999999993599997

Thus, as you get more and more monkeys, the probability of one of none of them typing banana on the first try approaches zero; at around 100,000,000,000 monkeys, the odds is: 0.0016615527035833107.

So, in the case of a single monkey at a single keyboard, given an infinite number of keystrokes and an infinite amount of time, the odds that it types banana is almost gauranteed.


This thereom has two very interesting takeaways in the context of fuzzing, what I am working on at Stellar.

  1. Given enough time (and this may be a LOT of time), almost all inputs will eventually be reached
  2. Given no direction, the odds of reaching all inputs in any reasonable amount of time is incredibly small

Thus, in implementing fuzzing for Stellar, I will need to use a fuzzer that is a bit smarter than a monkey and I will need to give it enough directions so it doesn’t bang away down nonsensical paths, investigating non-meaningful things.