Challenge 20: Overclocking

Update 2018/01/22: Bill Briere made quick work of this one and solved it in less than a day. He gets one point on the Leaderboard. I will post the solution soon.

---

Here’s Challenge 20 for January 21, 2018. It’s a picture puzzle:

Be sure to click the image to enlarge it. To win, you must provide the plaintext AND describe how the cipher works.

Here are a few hints:

1. It reads left to right. When you get to the end of a row, continue to the beginning of the next row.
2. An X in the plaintext could be an X or a Z.
3. The following symbol is a D:

---

With CodeAWeek.com, I hope to release one cipher, puzzle, or mystery each week. 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.