A Birthday Treasure Hunt With Three Cipher Levels

• Level 1: Caesar shift (ages 7+)
• Level 2: Affine cipher (ages 10+)
• Level 3: Vigenère (ages 12+ or adults)
• Practical tips
• Making the materials

Codes turn a treasure hunt into a mission. The trick for a mixed-age party is to raise the difficulty gently, so younger kids crack the first clue and older ones still have something to chew on at the end.

§Level 1: Caesar shift (ages 7+)

Write the first clue with a shift of 3, so A becomes D. Give every team a paper cipher wheel; turning the wheel is half the fun. Keep the message short, such as “LOOK UNDER THE MAT”.

§Level 2: Affine cipher (ages 10+)

The affine cipher multiplies each letter’s position before shifting. Print a small table of the result for each letter, so players only need to look things up. The clue can point to the next hiding place: “CHECK THE BOOKSHELF”.

§Level 3: Vigenère (ages 12+ or adults)

Use a short keyword, ideally the birthday child’s name. Each letter of the key gives a different shift, so letter-frequency tricks stop working. Give the keyword as a riddle on the previous clue.

§Practical tips

• Test each clue by decoding it yourself from the printed sheet.
• Use capital letters and leave spaces between words for younger players.
• Keep a spare answer sheet in your pocket in case a team gets stuck.

§Making the materials

The Caesar cipher wheel can be printed or shown on a tablet. The affine and Vigenère tools on caesarcipher.org let you encode each clue and double-check it before the party.

Disclosure: written by the caesarcipher.org team.