Exploring the Vigenere Cipher Answer Key


I noticed that on the answer key it stated that “The amount of shift is determined based on the “key” which translates letters of the alphabet to an amount of shift. So A=1, B=2, C=3 and so on.” Wouldn’t it be A=0, B=1 and C=2?


Hi @jmclean,

Thanks for alerting us to this! You are correct it should say A=0 B=1 C=2. I have updated the answer to reflect this.



CSP Team


Regarding the last bullet (“What if I told you that…”):
At the end of the first sentence of the prompt, should we clarify that "and the key I used was 10 characters long, without repeated characters. That way, the math of part 2 of the answer will be correct. The other option is to have the math read 26^10, however this allows for keys like AAA, BBB, etc which we established earlier in the worksheet were simple Cesar Ciphers. I would lean towards the latter, as we need to include keys like BDBD that have repeated characters. Sorry, it’s the math nerd in me.


I think you make a good point. I have noticed that sometimes the math get’s a little “hand-wavy” - some students LOVE the math, but others get nervous about it.

I wonder if there is a good space to guide math-y students to doing some more independent research on math-related topics in the practice PTs. For example, suggest students who like learning about the math research how the combinatorics behind certain encryption schemes works. That might provide some of those students more satisfying experiences with the content but also allow less confident math students to engage with the content in a different way.


Good idea, Kaitie. Maybe I’ll try this too.