Answer: Secret Code #145

The secret message says:

DATA

The shift was 9.

The secret note decoded: DATA
The note, decoded.

Letter by letter

Secret letterCJM
Real letterTAD

Decode it with Python

This program does the decoding for you. Change the secret and the shift to crack other messages!

secret = "MJCJ"
shift = 9
message = ""

for letter in secret:
    if letter.isalpha():
        number = (ord(letter) - ord("A") - shift) % 26
        message = message + chr(number + ord("A"))
    else:
        message = message + letter

print(message)

When you run it, it prints:

DATA

Did you know? Shift codes are very old. A Roman writer called Suetonius said that Julius Caesar wrote secret letters by shifting the alphabet by three. That’s why it’s often called the Caesar cipher.