Transposition ciphers

Transposition encryption methods involve rearranging data to be encrypted to make them incomprehensible. This may mean, for example, geometrically re-ordering data to make them visually unusable.

The Assyrian technique

The Assyrian cipher technique is probably the main proof that encryption methods were used in Greece as early as 600 BC to disguise messages written on papyrus strips.

The technique involved:

• rolling a strip of papyrus around a cylinder called a scytale;
• writing the text lengthwise on the rolled strip (the message in the example shown above is "comment ça marche").

The message, when unrolled, is no longer meaningful ("cecaeonar mt c m mh"). The recipient simply has to have a cylinder with the same diameter to be able to decrypt the message. In reality, a code-breaker (there were code-breakers at the time!) can decrypt the message by trying cylinders with a series of different diameters; this means the method can be broken statistically (the characters just need to be taken one by one, separated by a certain distance).

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