7934 /www/nrich/html/content/id/7934/ 1 2011-12-21T11:08:02 <mdoxml version="1.0"><p>This is the start of a six-part challenge.</p> <p><strong>Can you get to the end and crack the final message?</strong></p> <p>The ciphers in this challenge use some of the techniques discussed in the problems <a href="/4957">Substitution Cipher</a> and <a href="/7940">Transposition Cipher</a>, so you may want to have a go at those first.</p> <p>Each message when decrypted gives a small clue to how the next challenge has been encrypted, and gives you a keyword that allows you to access the next challenge.</p> <p>Good luck!</p> <p> </p> <h3>Part 1</h3> <div class="pdm">Ltaa sdct udg hdakxcv iwt uxghi du iwt CGXRW Hipvt Iwgtt pcs Udjg rxewtg rwpaatcvth! Iwxh inet du rxewtg xh rpaats p Rpthpg hwxui pcs xh cpbts puitg Yjaxjh Rpthpg, iwt Gdbpc Tbetgdg, lwd jhts xi id rdbbjcxrpit lxiw wxh vtctgpah. <p>Iwt htrdcs rxewtg rwpaatcvt lxaa jht p sxuutgtci btiwds du tcrgneixdc. Wtgt pgt hdbt ixeh id wtae ndj id hdakt xi:</p> <p>Pgt iwtgt pcn hxcvat atiitgh? Lwpi bxvwi iwtn qt?</p> <p>Pgt iwtgt pcn hwdgi ldgsh? Rpc ndj iwxcz du pcn hwdgi ldgsh iwpi pgt jhts duitc?</p> <p>Pgt iwtgt pcn pedhigdewth? Lwpi ldgsh sd ndj zcdl iwpi rdcipxc pedhigdewth? Sdth iwpi vxkt ndj pcn wxcih pqdji iwt atiitgh iwpi bxvwi qt jhts?</p> <p>Uxcpaan, ndj ctts id zcdl iwt ztnldgs id prrthh iwt htrdcs rwpaatcvt. Xi lph p rdas pcs vaddbn spn lwtc X lgdit iwxh egdqatb, hd X rwdht p qgxvwi pcs rwttguja ztnldgs: gpxcqdl.</p> </div> <p><br></br> If you want to work on a computer to solve the problem, you can download this cipher as a <a href="/content/id/7934/cipher1.txt">text file</a> which doesn&#39;t contain any line breaks.</p> <p>We have created a <a href="http://nrich.maths.org/7983">Cipher Challenge Toolkit</a> with some tools to help you crack different types of code.</p> <p> </p> <p><strong>Once you&#39;ve decrypted this message, you should have a keyword.</strong></p> <p>You can access Part 2 of the Cipher Challenge at http://nrich.maths.org/???<br></br> by replacing the ??? with the keyword.</p> <p> </p> <div class="framework"><strong>Notes and Background</strong><br></br> <br></br> You may find the Plus article <a href="http://plus.maths.org/content/cracking-codes">Cracking Codes</a> a useful and interesting read before embarking on the Cipher Challenge.</div></mdoxml> <mdoxml version="1.0"><h3>Why do this problem?</h3> <p>Together with <a href="/7943">Substitution Transposed</a>, this problem provides a challenging follow-up for students who have worked on <a href="/4957">Substitution Cipher</a> and <a href="/7940">Transposition Cipher</a>.</p> <h3> </h3> <h3>Possible approach</h3> <p>As this problem is quite lengthy, with some quite challenging codes towards the end, it could be offered as an extension for those students who have sailed through the easier codebreaking problems.</p> <p>One possible approach for the whole class is to divide the group up into teams so that each team can tackle the challenges collaboratively, in competition with the others.</p> <p>If a computer room is available, introduce students to the <a href="/7983">Cipher Challenge Toolkit</a> and give them plenty of time to explore it and learn how to use the tools.</p> <h3> </h3> <h3>Possible extension</h3> <p>The <a href="/7081">Stage 5 Cipher Challenge</a> offers a set of seven very difficult linked ciphers to crack.</p> <p> </p> <h3>Possible support</h3> <p>The challenges have been carefully chosen to get progressively more difficult; the first three should be accessible to anyone who has completed <a href="/4957">Substitution Cipher</a>.</p></mdoxml> <mdoxml version="1.0"><p>A good first step is to calculate the number of times each letter appears, and try to guess what type of cipher has been used.</p> <p>If it&#39;s a monoalphabetic cipher (one that substitutes the same letters throughout the message), you may be able to guess what the most common letters in the ciphertext are.</p> <p>You might then be able to guess what some of the short words are, particularly if they are repeated often in the message.</p> <p>If you get stuck on the later challenges, there are lots of articles online about different codebreaking techniques and cipher methods, so do a little research and then come back and try again.</p></mdoxml> <mdoxml version="1.0"><p>Caesar shift: p</p> <p> </p> <p>Well done for solving the first of the NRICH Stage Three and Four cipher challenges! This type of cipher is called a Caesar shift and is named after Julius Caesar, the Roman Emperor, who used it to communicate with his generals.</p> <p>The second cipher challenge will use a different method of encryption. Here are some tips to help you to solve it:<br></br> Are there any single letters? What might they be?<br></br> Are there any short words? Can you think of any short words that are used often?<br></br> Are there any apostrophes? What words do you know that contain apostrophes? Does that give you any hints about the letters that might be used?</p> <p>Finally, you need to know the keyword to access the second challenge. It was a cold and gloomy day when I wrote this problem, so I chose a bright and cheerful keyword: rainbow.</p></mdoxml> 2 4 0 0 1 1 0 Here is the start of a six-part challenge. Can you get to the end and crack the final message? Applications Codes and cryptography Handling, Processing and Representing Data Comparing data Handling, Processing and Representing Data Frequency tables and diagrams