Caesar Cipher Lab: Check Your Shift Direction
A Caesar cipher moves every letter by the same number of positions. Before trying to decode a message, write down your alphabet and whether the key means a forward or backward move. Use A=0 through Z=25 for the arithmetic below.
A worked example
With a forward shift of 3, A becomes D and Z wraps around to C. HELLO becomes KHOOR. To recover HELLO, subtract 3 rather than shifting forward another 3 places. In arithmetic, encryption is (x+3) mod 26 and decryption is (x-3) mod 26.
Try it yourself
1. Predict the output for XYZ at key 3 before using a tool.
2. Check that the result is ABC.
3. Decode ABC with the same key and confirm XYZ returns.
4. Repeat with a sentence containing punctuation. Record whether spaces and punctuation are preserved by your chosen tool.
Interactive practice: https://caesarcipher.org/ciphers/caesar
More classical cipher learning tools: https://caesarcipher.org/
Common mistakes
Counting A as 1 while using a formula that expects A=0 creates an off-by-one error. Mixing forward and backward key conventions creates another. If your decoded output is nonsense, inspect these conventions before guessing another cipher.
For an unknown key there are only 26 rotations, including the unchanged text. Read several candidate outputs and judge them in context; a very short sample can have several plausible answers. Classical ciphers are educational examples and are unsuitable for protecting private information.