UPDATE 2017/09/23: This post has been solved! View the solution here.

Here’s Challenge #7 for September 20, 2017. (Published a bit late. My apologies.)

A SIMPLE SUBSTITUTION

Today’s cipher is a one-step polyalphabetic substitution that’s not a Vigenère. If you know how to count, you shouldn’t have a problem figuring out this method.

The answer is a quote from a famous book on arithmetic.

The ciphertext is:

X K W L Y N L A N X

T Z R T X W L J X M

V J A U H T I V K I

X O N V I O C A J V

X S Y L A Y V N X Z

R C B N O D J V O Q

A K Y K A I B R V J

P B V P P M D V F T

L W B X P B C O Y R

V P D D R U V C

Good luck!

With CodeAWeek.com, I hope to release one cipher, puzzle, or mystery every Wednesday evening. Anyone can attempt to solve. The winner is the first person to send a correct solution and a description of the solve method to codemaster@codeaweek.com. Once a correct solution is e-mailed, I will publish a follow-up post, congratulating the winner and revealing the secrets of the code.

You may post questions or theories in the comments, but DO NOT POST SOLUTIONS. E-mail them to codemaster@codeaweek.com.