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Polybius square
In cryptography, the Polybius square, also known as the Polybius checkerboard, is a device invented by the Ancient Greek historian and scholar Polybius,〔(Hist. X.45.6 ff. )〕 for fractionating plaintext characters so that they can be represented by a smaller set of symbols.
==Basic form ==
The original square used the Greek alphabet, but can be used with any alphabet. In fact, it has also been used with Japanese hiragana (''see cryptography in Japan''). With the modern English alphabet, in typical form, it appears thus:
Each letter is then represented by its coordinates in the grid. For example, "BAT" becomes "12 11 44". Because 26 characters do not quite fit in a square, it is rounded down to the next lowest square number by combining two letters (usually I and J). (Polybius had no such problem because the Greek alphabet he was using had 24 letters). Alternatively, the ten digits could be added and 36 characters would be put into a 6 × 6 grid
Such a larger grid might also be used for Cyrillic script (of which the most common alphabet variant has 33 letters, though some have fewer, and some up to 37.)
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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