A Roman conversion?

7704 /www/nrich/html/content/id/7704/ 1 2011-10-24T11:53:39 <?xml version="1.0" encoding="UTF-8"?> <mdoxml version="1.0"> Zhoo grqh, brx'yh fudfnhg wklv frgh! Kdyh brx zrunhg rxw krz wklv phvvdjh kdv ehhq hqflskhuhg? Wkh ohwwhu 'd' zdv pdsshg wr 'g', 'e' wr 'h' hwf. Wklv lv fdoohg d Fdhvdu vkliw, zlwk d vkliw ri wkuhh ohwwhuv lq wklv fdvh. Zh dovr pdgh wklqjv d elw hdvlhu eb ohdylqj sxqfwxdwlrq dqg wkh vsdfhv ehwzhhq wkh zrugv lq. Krz glg brx ghflskhu wklv? Brx pdb kdyh wulhg orrnlqj iru uhshdwhg wkuhh ohwwhu zrugv vxfk dv 'wkh', ru frxqwhg krz pdqb ri hdfk ohwwhu dsshduhg lq wkh flskhuwhaw dqg jxhvvhg wkdw wkh prvw frpprq ohwwhu fruuhvsrqgv wr 'h'. Wklv vhfrqg phwkrg lv wkh edvlv ri d phwkrg fdoohg iuhtxhqfb dqdobvlv dqg lv yhub xvhixo iru prqrdoskdehwlf flskhuv. Li brx nqrz krz wr surjudp, brx fdq vdyh brxuvhoi d orw ri wlph eb zulwlqj vrph frgh wr gr lw iru brx! Grq'w zruub li brx grq'w wkrxjk, wkhuh duh orwv ri zdbv brx fdq gr lw. Wkh 'ilqg dqg uhsodfh' wrro lq d zrug surfhvvlqj surjudp fdq eh yhub xvhixo, mxvw pdnh vxuh brx grq'w fkdqjh djdlq wkh ohwwhuv brx'yh douhdgb uhsodfhg! Rqh zdb durxqg wklv lv wr wxuq wkh zkroh phvvdjh lqwr orzhu fdvh, dqg wkhq xvh fdslwdov iru wkh ghfusbwhg phvvdjh. Wkh qhaw phvvdjh zloo eh voljkwob kdughu, jrrg oxfn! </mdoxml> <?xml version="1.0" encoding="UTF-8"?> <mdoxml version="1.0">Have you managed to solve the entire <a href="http://nrich.maths.org/7081">Stage 5 Cipher Challenge</a>? Solutions are now closed, but perhaps you want to take up the full challenge. Successful solvers of this part were Amy, England Khishigbadral Ganzorigt, Li Po Chun United World College, Hong Kong Ibrahim EL-Serafy, Slough Grammar School, England Ben James, Wilson's School, United Kingdon Mahdokht Mohamady, Farzanegan of Kermanshah Patrick, Woodbridge School, England Narika and Juhi, Claremont High School Academy Trust, England Jasmine Velani, Salcombe Preparatory Luke, Cottenham Village College, England Louis, Parkside School, England Rhea from England Matthew from Wilson's School, England An Anonymous Solver, from Somewhere Jospeh, from Hong Kong Adam, from England Well done to you all! The solution is as follows Well done, you've cracked this code! Have you worked out how this message has been enciphered? The letter 'a' was mapped to 'd', 'b' to 'e' etc. This is called a Caesar shift, with a shift of three letters in this case. We also made things a bit easier by leaving punctuation and the spaces between the words in. How did you decipher this? You may have tried looking for repeated three letter words such as 'the', or counted how many of each letter appeared in the ciphertext and guessed that the most common letter corresponds to 'e'. This second method is the basis of a method called frequency analysis and is very useful for monoalphabetic ciphers. If you know how to program, you can save yourself a lot of time by writing some code to do it for you! Don't worry if you don't though, there are lots of ways you can do it. The 'find and replace' tool in a word processing program can be very useful, just make sure you don't change again the letters you've already replaced! One way around this is to turn the whole message into lower case, and then use capitals for the decrpyted message. The next message will be slightly harder, good luck! Caesar shift +3</mdoxml> <?xml version="1.0" encoding="UTF-8"?> <mdoxml version="1.0">This challenge cipher forms part of a very difficult <a href="http://nrich.maths.org/7081">sequence of ciphers</a> suitable for keen groups or individuals, maths clubs and very optional homework challenges. Don't try this in the classroom!</mdoxml> <?xml version="1.0" encoding="UTF-8"?> <mdoxml version="1.0">This is the first of our <a href="https://nrich.maths.org/7081">challenge ciphers</a>. We recommend that you attempt them in order, as the solution of each challenge gives a small (and necessary!) hint for the next challenge.</mdoxml> <?xml version="1.0" encoding="UTF-8"?> <mdoxml version="1.0"> Well done, you've cracked this code! Have you worked out how this message has been enciphered? The letter 'a' was mapped to 'd', 'b' to 'e' etc. This is called a Caesar shift, with a shift of three letters in this case. We also made things a bit easier by leaving punctuation and the spaces between the words in. How did you decipher this? You may have tried looking for repeated three letter words such as 'the', or counted how many of each letter appeared in the ciphertext and guessed that the most common letter corresponds to 'e'. This second method is the basis of a method called frequency analysis and is very useful for monoalphabetic ciphers. If you know how to program, you can save yourself a lot of time by writing some code to do it for you! Don't worry if you don't though, there are lots of ways you can do it. The 'find and replace' tool in a word processing program can be very useful, just make sure you don't change again the letters you've already replaced! One way around this is to turn the whole message into lower case, and then use capitals for the decrpyted message. The next message will be slightly harder, good luck! Caesar shift +3 </mdoxml> 2 5 0 0 0 0 1 A Roman conversion? First cipher Applications Codes and cryptography