1. http://nrich.maths.org Transposition Cipher

2. http://nrich.maths.org Suppose we want to encrypt the following message: “Now run along and don't get into mischief, I'm going out.” from “Peter Rabbit” by Beatrix Potter

3. http://nrich.maths.org Start by removing the punctuation and the spaces between the words: nowrunalonganddontget intomischiefimgoingout

4. http://nrich.maths.org Add 4 extra padding characters at the end, to take the message up to 48 characters: nowrunalonganddontgetin tomischiefimgoingoutxxxx

5. http://nrich.maths.org Write this message in 4 rows, each 12 letters long: nowrunalonga nddontgetint omischiefiam goingoutxxxx

6. http://nrich.maths.org Read the letters in order down the columns, instead of along the rows: nowrunalonga nddontgetint omischiefiam goingoutxxxx nnogodmowdiiroshuncgntho agiuleetotfxniixgnaxatmx

7. http://nrich.maths.org Suppose the enemy intercepts and wants to decipher our message. What might they do?

8. http://nrich.maths.org 48 characters can be encoded using grids of one of these dimensions: 1×4848×1 2×2424×2 3×1616×3 4×1212×4 6×88×6

9. http://nrich.maths.org n nogodmowdiirosnuncgntho a giuleetotfxniIxgnaxatmx 1×48 doesn't rearrange the message at all. 2×24 gives: Reading down the columns gives "nangoigu...."

10. http://nrich.maths.org Next we try a 3×16 grid. And then a 4×12 grid. And then …

11. http://nrich.maths.org n nog o dmo w dii r osn u ncg n tho a giu l eet o tfx n iIx g nax a tmx Eventually we get to the 12×4 grid. This time, reading down the columns gives us the original message!