Have them read Edgar Allan Poe’s The Gold-Bug, which is basically the story of someone going through the process of breaking a simple substitution cypher. I found it enjoyable when I read it about that age. (I actually read a “Children’s version” of the story, but it kept all the crypto, just lowered the reading level.)
Then give them similar problems to the one in the book and have them break it by looking for character frequencies to guess the cypher.
Try the Vigenère cipher. It’s easy if you know Babbage’s method (AKA Kasiski examination), but otherwise should be pretty challenging. Another advantage is that it has a lot of factors that could be manipulated to change the difficulty of the task, e.g. the key size or single letters of the plaintext.
Which kind of cryptography puzzles would appeal to a child who is doing fifth grade math level work?
Have them read Edgar Allan Poe’s The Gold-Bug, which is basically the story of someone going through the process of breaking a simple substitution cypher. I found it enjoyable when I read it about that age. (I actually read a “Children’s version” of the story, but it kept all the crypto, just lowered the reading level.)
Then give them similar problems to the one in the book and have them break it by looking for character frequencies to guess the cypher.
There’s a Sherlock Holmes story, The Adventure of the Dancing Men, that has the same thing.
Try the Vigenère cipher. It’s easy if you know Babbage’s method (AKA Kasiski examination), but otherwise should be pretty challenging. Another advantage is that it has a lot of factors that could be manipulated to change the difficulty of the task, e.g. the key size or single letters of the plaintext.