High Quality Content by WIKIPEDIA articles! The cipher system that Uesugi used is basically a simple substitution usually known as a Polybius square or “checkerboard.” The i-ro-ha alphabet contains forty-eight letters, so a seven-by-seven square is used, with one of the cells left blank. The rows and columns are labeled with a number or a letter. In the table below, the numbers start in the top left, as does the i-ro-ha alphabet. In practice these could start in any corner.