The Greek Square Cipher or the Polybius Checkerboard
This week’s cypher is based on a system developed by Polybius, a Greek historian and cryptographer, about 2,000 years ago.
54 34 45 / 32 45 43 44 / 13 23 11 33 22 15 / 24 33 / 34 42 14 15 42 / 44 34 / 43 45 42 51 24 51 15
The key to this code is made by setting up a 6 x 6 square. Leaving the first square blank, number 1 – 5 down and across. Then fill in the remaining squares with the alphabet. Since the English alphabet has 26 letters, it will not fit. I and J occupy the same space, number 24. To encode something, determine first the row then the column number for each letter. A = 11, Z = 55, S = 43.
To determine if a Greek Square is being used, notice that all letters have two numbers and no number is higher than 55.
| 1 | 2 | 3 | 4 | 5 | |
| 1 | A | B | C | D | E |
| 2 | F | G | H | I, J | K |
| 3 | L | M | N | O | P |
| 4 | Q | R | S | T | U |
| 5 | V | W | X | Y | Z |
The solution to this week’s cipher is:
You must change in order to survive. ~ Pearl Bailey