Secondary cipher challenge part 6

7939 /www/nrich/html/content/id/7939/ 1 2011-12-21T11:18:06 <?xml version="1.0" encoding="UTF-8"?> <mdoxml version="1.0">This is the last part of the <a href="/7934">Secondary Cipher Challenge</a>. <h3>Part 6</h3> <div class="pdm"> Kn pqf gcv iglh vpzu, gitg ngwp fweg! Elka fpp aca mgcc vwlis! Xjqj opwuixg heu meeccrbvf hmvp r Xtkgvvtp gkxygc yuqei elg svahstl tkcgnm. Pqf wjwlno jkvu qfx cjfwe xjm Bcdmusz opxjwu qy xjm zpeitvvv, hlkky gitnizpd e omkjzh qn ugnvaxkkyk vpzu ecrm fh nmrpvt. Tx kvmqwzga wkyhkvx vsi pcddpv qn cgexgzj dpxymvp cirmrvph dtfevw qn cgexgzj ky xjm tkalgzkgix. Vpzu tw nqbgwc vw sg l qwtkkapg ww vsi nmeiel qn kjp oggnqch. Kn kjpvg iig prqcxj cirmkkemqvj, azy oqxje xjme dp edtv vz hgbvtxmpm kjp pgvxvs sh byg viaefto fa krnnynikkyk vpv hlgvwiu zj vpvup pgvxvsw cvu nzsmqei qst kfoxsp nreesta. Njj rqb ktj epl ttpevm pqfv qee ettjmi cyh vmjv tx qv pqfv hzzgyhu vfy! </div> If you want to work on a computer to solve the problem, you can download this cipher as a <a href="/content/id/7939/cipher2.txt">text file</a> which doesn't contain any line breaks. You can use the <a href="http://nrich.maths.org/7983">Cipher Challenge Toolkit</a> to help you decipher it. If you have managed to solve Part 6, do submit a solution to tell us the techniques you used to solve the Cipher Challenges.</mdoxml> <?xml version="1.0" encoding="UTF-8"?> <mdoxml version="1.0">This one was fun! Here are some of the insights we got. Andie, from Nottingham Girls' High School, said: For part 1, you have to work out what 'I' and 'A' are and then you can carry on. Correct - why do you think that's easiest? The keyword here was "rainbow". Andie also gave us a hint for part 2: For part 2, you swap A with Z, B with Y, and so on. So: <pre> ABCDEFGHIJKLMNOPQRSTUVWXYZ </pre> <pre> -------------------------- ZYXWVUTSRQPONMLKJIHGFEDCBA </pre> and the keyword is "teacake". Aleena, Tiana, Katie and Lottie, from the same school, gave us their thoughts on part 3: We have found out the code to part 3. To find the code, you have to figure out what the letters represent. The lettersare jumbled up rather than just shifting it or reversing it. This makes the code harder to crack. But there a loads of clues to help you crack it. Example: A-E B-P C-G Great - and the keyword was "musical"! Pranjali, Lottie, Tiana and Katie noticed the trick for part 4: To crack the code in part 4, you had to notice that it was all in a spiral! All the words were jumbled up, and you had to figure them out separately. Correct, and the keyword here was "cheese". Thanks also to Rosie, Livvy, Georgina, Lucy, Alina, and others, who also submitted solutions. By the way, the keyword for part 5 was "special". Congratulations if you managed to break all of the codes!</mdoxml> <?xml version="1.0" encoding="UTF-8"?> <mdoxml version="1.0">If you can read this, very well done! This one was very tough! This message was encrypted with a Vigenere cipher using the keyword circle. You should find out about the Kasiski method on the internet, which explains a method of decrypting this type of cipher. It involves finding the number of letters between repeated blocks of letters in the ciphertext. This is likely to be a multiple of the length of the keyword. If there are enough repetitions, you might then be able to determine the length of the keyword by calculating the factors of these lengths and looking for common factors. Why not try and create your own cipher and test it on your friends now! Keyword: circle</mdoxml> 2 5 0 0 1 1 0 Secondary cipher challenge part 6 Here is the final part of a six-part challenge. Can you crack the final message?