Code of the Week!

view of the enigma machine

For your chance to win your very own signed copy of Simon Singh's Code Book try out your codebreaking skills with the "Code of the Week".

Solution for the "Code of the Week!" week starting 3rd March 2008

This hot country with a population of approximately twenty million is in the Southern Hemisphere where guys are referred to as blokes and girls are sheilas

The country is: Australia

Code of the Week 16 (week starting 3rd March 2008

Playfair Cipher

The Playfair Cipher uses a 5x5 grid containing a keyword. The keyword is written across the first cells of the square. The keyword that is used in this Playfair Cipher is "ENIGMA"


E

N

I

G

M

A

B

C

D

F

H

K

L

O

P

Q

R

S

T

U

V

W

X

Y

Z

To decipher the Playfair cipher, you must consider where the pair of letters are in the grid. The letter pair will fall into one of three categories both letters are in the same row, or both letters are in the same column, or the letters share neither a row nor a column.

  1. If both letters are in the same row, then they are replaced by the letters to the immediate left of each one. 'GI' becomes 'IN'. If a letter is at the beginning of a row, it is replaced by the letter at the end; 'HK' becomes 'PH'.

  2. If both letters are in the same column, then they are replaced by the letter immediately above each one; 'CL' becomes 'IC'. If a letter is at the top of a column, it is replaced by the letter at the bottom; 'GD' becomes 'YG'.

  3. If the letters are neither in the same row nor the same column, the rule differs. To decipher the first letter, look along its row until you reach the column containing the second letter; the letter at this intersection replaces the first letter. To decipher the second letter, look along its row until you reach the column containing the first letter; the letter at the intersection replaces the second letter. Hence, 'TL' becomes 'SO'.

You can use this set of "Golden Rules" to decipher the Code of the Week

For more information on the Playfair Cipher see http://en.wikipedia.org/wiki/Playfair_cipher

Good luck!

Where in the world?

Ciphertext

QO CX KP SD PT GR TW XN QO FH PH SP DQ GL GK AB LZ KU LY GE DQ IH GY VN GR ZG CS SC KG CX GI QO IQ PT QO NQ EK NE CX HK NQ NV QA QN MT XT BQ NQ MA NQ QN OY HD RC OP HN QC GB MG SK QC QN QL NG HC XI