CAESAR CIPHERS
Codes used for messages, ciphers, and the breaking of these codes, have been of importance in espionage (e.g. the breaking of the German 'Enigma' cipher in the Second World War was vital) but it is now industrial espionage that is more likely to use ciphers than international spies!
Here is a message in cipher code.
F R P HW R P S K H O S Q R Z
Can you crack It? It is an example of a SHIFT cipher in which each letter has been shifted a certain number of places along the alphabet.
Problem 1Given that the shift is of length 3, decode the message above.
An easy way to decipher messages that have used a shift is to construct two concentric circles with the alphabet spread out equally on each circle (see reverse of sheet). The inside circle can be rotated to the desired position. This type of cipher is known as a CAESAR SHIFT as it was first used by Julius Caesar.
Problem 2Decipher the following messages:
a)PSXN YED XKWO YP ZOBCYX MKBBISXQ ZVKXC (shift 10)
b)HNK VBIAXK BL UKHDXG NLX T GXP HGX (shift 19)
c)XI HIN WIHNUWN GY ZIL NQI QWEM (shift unknown).
It is not difficult to break a single shift cipher, so various complications have been introduced. One of these requires having a KEY, which is a set of numbers, such as
7 3 9 1 6
and this tells you the shift used for each letter of the message. For example, in the message shown below, this key is used to determine the shift for each letter
DH FJRS EAJTN KNMV HW MBCU
73 9167 39167 3916 73 9167
Problem 3Decode this message.
Problem 4Use the KEY8421to code the message
MEET AT THE STATION AT MIDDAY
EXTENSION Design your own cipher using a KEY and see if anyone can crack it.
This is the first of a series of sheets on ciphers which are a special form of codes. They were crucial for Allied success in both World Wars and although still used in spying, they are now of more importance in international industrial espionage. This sheet deals with SHIFTS, and you might find it helpful to use the the two templates below for determining what a particular shift does.
ANSWERS
1.COME TO MY HELP NOW.
2.a) FIND OUT NAME OF PERSON CARRYING PLANS. b) OUR CIPHER lS BROKEN USE A NEW ONE.
c) DO NOT CONTACT ME FOR TWO WEEKS (shift of 20, or 6 in reverse direction).
3.WE WILL BRING HELP AT DAWN.
4.UIGU IX VIM WVBBMQO IX OJLHCZ