How is the Checkerboard Cipher structured?

The Checkerboard Cipher is structured in a way that requires a Polybius square, which is a grid used to encode letters into pairs of numbers. This grid is often personalized with a keyword that determines the arrangement of the letters within it, following the principles of the Polybius square system. In the classic setup, each letter of the alphabet is linked to a two-digit coordinate based on its position in the grid.

The use of a keyword allows for a more secure encoding by rearranging the letters based on the keyword’s placement, thereby ensuring that frequently used letters in plain text do not correspond to the same numbers as they typically would without such a setup. This adds a layer of complexity to the cipher that enhances its cryptographic strength.

While other choices mention aspects that are unrelated to the structure of the Checkerboard Cipher itself, the key aspect lies in its dependence on the Polybius method combined with the keyword setup, facilitating the method of encoding and decoding messages effectively.