WAIEL JASLE PTEGS RAELD A!

Well done for cracking the code! Now read on...

The next type of cipher we’re going to play with is substitution. The letters of the plain-text alphabet are substituted by others according to any number of possible systems. The simple Caesar cipher involves rotating the alphabet along a particular number of letters – if rotating along three letters (ROT-3, as it would be abbreviated), we’d encrypt ‘alphabet’ as ‘doskdehw’. We’re going to use something slightly trickier for this puzzle – a key-based substitution. Let’s take as our example the key phrase THE DANA CENTRE. We write out the plain-text alphabet A to Z, then write our key underneath (ignoring duplicates) first of all and then continue with the remaining letters in alphabetical order.

So WELCOME TO CRACK THE CODE! would encrypt to the title of this page.

Notice how it’s like a variable rotation, where the code alphabet reverts back to the plain-text alphabet after the last letter of the keyword is reached (U–Z in our example)?

As this cipher only uses one code alphabet, it’s known as monoalphabetical. This makes it relatively easy to crack – frequency analysis is one useful tool if we know the language it’s written in. As E is the most common letter in English, then we’d expect a message encrypted using the above to have E (coincidentally) as the most common letter.

Polyalphabetical substitutions have many code alphabets that the coding process switches between, so the first letter is coded with one code alphabet, the second with another, and so on. The famous Enigma machine that encrypted Germany’s communications during the Second World War used a fiendishly complicated polyalphabetical substitution, where the mechanism clicked into a new code alphabet every time a character was encrypted.

Here’s the next puzzle – not an Enigma! It may look very long, but that length will help you when it comes to analysis – and although there’s no punctuation, I decided to leave the word groupings in after my guinea pigs fed back their comments. When you’ve decrypted it all, you’ll know what to do next. Two spoiler clues follow but I’ll tell you two things that may help – it’s in English (phew!) and it’s a letter to me from the expert who is our mystery setter.

TCBN FIGAEB

AQ VADD LC NBQPCN HSG AH ISN BSTACGEC TIG’Q KGIV BQ QPC ISQOCQ VPAEP IH SO CWJCNQO AO QPC FXOQCNX OCQQCN. ESNAIOAQX FBX KADD EBQO LSQ AQ ECNQBAGDX VPCQO QPC PSFBG BJJCQAQC, BGT A GCUCN FSEP EBNCT HIN EBQO. B ENXJQIYNBJPCN VISDTG'Q TCAYG QI YCQ ISQ IH LCT VAQPISQ ESNAIOAQX, DCQ BDIGC TCTAEBQC QPCAN DAHC QI YNBJJDAGY VAQP QPC VAQO IH QPC CGCFX.

BO B JDBAGQCWQ HIN QPC KCX JPNBOC OSLOQAQSQAIG, VPX GIQ SOC QPAO FCOOBYC? QPCNC BNC CBOX EIGQCWQSBD EDSCO. NAEPBNT, CUCN QPC JNCEIEAISO IGC, OSYYCOQO QPCX CFBAD XIS BQ XISN OEACGEC FSOCSF TIQ INY BTTNCOO VAQP QPC KCX JPNBOC JDBEC BO QPC OSLRCEQ PCBTAGY. A BF OSNC QPAO VADD FBKC OCGOC QI XIS, AH A PBUC FX TIQO BGT INYO EINNCEQ. A BF OQADD BFBZCT BQ PIV CBOADX PATTCG AG QPC JPIQI IH XISN PBGT IG KCXLIBNT AO QPC QAGXSND EITC HIN FX BTUBGEC NBFLDAGYO.

KAGT NCYBNTO

RIBG

Best wishes

Monica Smith
Programmes Developer
Dana Centre

4 points for solving it...

...but you'll lose 1 by clicking for a mild spoiler clue HERE

...and you'll lose 2 by clicking for a big spoiler clue HERE

By the way, there’s no guarantee that your friends will be on the same team as you on the night – so don’t give clues away cheaply!