so, the first well known cypher, a substitution cypher, was called the “caesar cypher,” because, apparently, Julius caesar used it in 58 bc. he shifted each letter in his military commands to encrypt his messages, so if the enemy intercepted it, they would make no sense. Lets say Alice and Bob used a Caesar cypher to communicate from a distance without Eve (a codebreaker who is always listening) Knowing what they are saying. first, they would have to agree on the shift, say 3. so, every letter should be shifted by 3. so

a = d

b = e

c = f




and so on. so this message:


would become:


that is super weird! so… how could Eve break this? well…a lock is only as strong as its weakest point. so… this is a pretty weak cypher. this is called a “Leak Of Information” and it was found by an Arab mathematician 800 years layer. he broke the Caesar cypher by using a important property of english. if you count up the letters of any book and look at which letters are most common, you see this pattern:

but, if eve looked at this message and found that H was the most common letter, then she could deduce that the shift was probably 3. so… how do we stop the leak? that is for part two!
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