DIANA cryptosystem
A one-time pad you can really use: one table, no arithmetic, and it works both ways round.
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Scytale
A rod and a paper strip. The oldest code machine there is, and it takes five minutes.
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Caesar wheel
Two card discs and a split pin. Turn it and the whole cipher changes.
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Alberti disk
The same build with a scrambled inner ring. Turn it mid-message and you have invented a harder cipher.
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Cardano grille
A card with windows cut in it, so a dull letter about the weather carries a secret.
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Rotating grille
A six by six card that turns four times and fills every cell. Working out where to cut is the puzzle.
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Jefferson wheel
Six rings of letters on a pencil, invented by a president and still in use a century later.
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Knot code
A length of cord and a marked strip. A message you can wear on your wrist.
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Semaphore flags
Two dowels and two tea towels. Best used across a garden at a shouting distance.
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Morse signal lamp
A torch, a code card in your pocket, and a friend at the end of the garden.
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Invisible ink
Lemon juice and a warm lamp. An adult holds the lamp, and never a flame.
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Paper cone record player
A sewing needle, a paper cone and an old record. No electricity, and you will hear music come out of a scratch.
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Music box drum
A comb, a cardboard tube and pins. Turn it and you have built a machine that remembers a tune.
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Before you print a template
Printers shrink pages unless you stop them. Set the scale to 100 per cent, not fit to page, or your two discs will not line up. Every template carries a ruler line so you can check.
Print the sheets