Taking codebreaking, mathematics, intrigue and strategy into the classroom and beyond
The Babbington Plot - Teachers' notes
This exercise relates directly to the tale of Mary Queen of Scots the students heard during their Enigma Project visit.
By tallying the frequency of the symbols of the message, children should be able to identify the most commonly used letters in English (E, T, A and N) and then should be able to use reasoning, familiarity of the English language and their knowledge of the story to work out the rest of the message. It will not take long to count the frequencies in this extract. Letter frequencies fit those that you might expect for common letters.
The Plaintext message is:
To Anthony Babbington, I agree that you can murder Queen Elizabeth at the earliest time. From Mary.
Hints to give pupils as needed:
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What are the most common symbols in the coded message? Perhaps they match the most common letters in English, which are E, T, A and N.
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Can you guess any parts of the message? Who might it be to and who might it be from?
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Focus on any 1-letter words. What words have only 1 letter?
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Focus on any 3-lettter words. What are the common 3-letter words in English?
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If you know the story of Mary, who might she talk about in the message?
Further facts about the English language:
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The most common 2 letter words in English are: of, to, in, it, is, be
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The most common 3 letter words in English are: the, and, for, are, but
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The most common starting letters for words are: t, o, a, w, b
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The most common ending letters for words are: e, s, t, d, n
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The most common repeated letters are: ss, ee, tt, ff, ll, mm, oo
Follow up work on 'The Code Book CD-ROM'
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There are several texts in the 'Frequency Analysis Puzzle' suitable for children. On the puzzle page, click on 'Pick Ciphertext'. The junior puzzles are on the left. Ones particularly good for beginners include: 'The Mole', 'Alice in Wonderland', 'Ox and the Frog' and 'Mowgli'.
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Once the students are familiar with how the program works, you could set up a competition, working in groups to try and get the fastest time to solve a particular text. The clock starts running as soon as the text is chosen.
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The 'Frequency Analysis Tool' can be used to check the frequency of letters in everyday English. Texts can be cut and pasted into the Ciphertext box and the frequency of the letters found by using the 'Frequency of Individual letters' tool. Students can investigate the frequency of letters in different types of text eg The Times vs. The Sun (which should be the same if a large enough sample is used), or indifferent languages eg English vs. French.
The Babbington Plot
The following note has been coded using the cipher actually used by Mary Queen of Scots.
Can you crack it?
Frequency table
|
Symbol |
Tally |
Frequency |
|
|
||
|
Δ |
||
|
Ø |
||
|
O |
||
|
8 |
||
|
C |
||
|
|
||
|
∞ |
||
|
θ |
||
|
|
||
|
f |
||
|
|
||
|
m |
||
|
9 |
||
|
ą |
||
|
η |
||
|
ε |
||
|
|
||
|
|
||
|
|
||
|
|
Total |
81 |
The Enigma Project is part of the family of activities in the Millennium Mathematics Project, which also includes the Hands On Maths Roadshow and the NRICH, Plus and Motivate websites
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