This is a classical cipher from 16th century Japan.
The Uesugi cipher is described in a military strategy book written by Sadayuki Usami, a military strategist in the Sengoku period (under Uesugi Kenshin, a warlord of the period).
The cipher uses a 7x7 grid. You write down the 48 characters of the Iroha syllabary in the 7x7 grid, with one square being left empty. After that, each character can be encoded as two numbers: the first number corresponds to the row, and the second number corresponds to the column.
This is similar to a Polybius square.
Table
七 | 六 | 五 | 四 | 三 | 二 | 一 | |
---|---|---|---|---|---|---|---|
ゑ | あ | や | ら | よ | ち | い | 一 |
た | り | ろ | 二 | ||||
れ | ぬ | は | 三 | ||||
そ | る | に | 四 | ||||
つ | を | ほ | 五 | ||||
ね | わ | へ | 六 | ||||
な | か | と | 七 |
Cultural references
In Dr. Stone: Science Future, the Uesugi cipher is used for radio communication without the messages being intercepted by the enemy. The messages are intentionally kept brief, to avoid making Frequency analysis possible.