This task tests your understanding of encryption, and its uses. Encryption is an interesting and important technique that is used to keep our information secure when we transmit it across the internet.
The following links might also interest you if you like this task:
Bletchley Park - the site of code-breaking activities during the second world war, and now a museum near Milton Keynes
GCHQ - the government's replacement for Bletchley Park, which was established after the war
Enigma Simulator - a web-page that shows you how an Enigma machine works
Paper Enigma - print yourself a machine to encipher and decipher messages
Substitution Ciphers - decrypts substitution ciphers; a web-based alternative to using the Vignere Square below
NB. All links on this page open in a separate tab or window so that you can have the two pages open at the same time.
A substitution cipher is one in which letters are represented by other letters. It can be deciphered by someone knowing the order of the cipher alphabet used.
One method of hiding messages in this way was invented by Julius Caesar, a Roman Emperor over two thousand years ago. It is known as the Caesar cipher.
To encode a message, for example:
THIS CODE WAS INVENTED BY JULIUS CAESAR
take each letter, go three along the alphabet and use that letter instead (e.g. A becomes D, B becomes E, etc. - see the Vignere Square at the bottom of this task). The message then becomes:
WKLV FRGH ZDV LQYHQWHG EB MXOLXV FDHVDU
It looks strange, doesn't it? That's because the letters don't appear with the same frequency as they do in English (e.g. there are more Qs and Xs than in real words), and there's no U after the Q, etc.
What does the following message say? The letters might not be shifted by three, like they are in the example.
JRQH WR ZDWFK KDUOHTXLQV. EDFN DW VHYHQ.
BPQA PIA JMMV APQNBML JG MQOPB
VXKT BT RWTTHT EATPHT
In a Caesar shift cipher, all of the letters in the alphabet are still in order, it just starts in a different place. If the coded alphabet is not in order, we have what is called a substitution cipher, for example:
This is more secure because there are many more possible ways of decoding the message and each letter must be worked on separately..
ZHCVHYP NYDCTG SJL GCMO
E T A O N R I S H D L F C U M G P Y W B V K X J Q Z
You will probably need a pen and piece of paper to help you make a table of likely substitutions - or you could use a web-page such as this: Decipher.
AUHC MVKFC V BYZUGC V IZMC CJ GUMBZYAZD UKUVM VC HZZGZB CJ GZ HCJJB PD CFZ VYJM KUCZ AZUBVMK CJ CFZ BYVWZ UMB OJY U IFVAZ V TJNAB MJC ZMCZY OJY CFZ IUD IUH PUYYZB CJ GZ