Year 8 Cryptography

The topic for Year 8 ICT this Half Term is “Crytpography” (which links in with their History trip to Bletchley Park later in the term). In the first week we discussed the topic of code-breaking and cryptography and the children were set the challenge of cracking a code. They were given a piece of text that had been encrypted using a simple Caesar cipher and asked to work in pairs to crack the code and they were given no further information. The quickest pair cracked the code in 15 minutes.

This week we discussed why certain data we send over the Internet would need to be encrypted such as bank details. We looked at the idea of encryption keys and how algorithms were used to encrypt the data and the key was needed to unlock the code at the receivers end.

The children were then presented with a series of encrypted co-ordinates such as…


Key = 5

They were told that the original co-ordinates had been encrypted by adding the key to each digit, then dividing by the key and finally subtracting the key.

To decrypt the co-ordinates they had to do the inverse so they first split the code into pairs of digits and added the key…

50 35 . 25 40 35 , 20 . 30 45 60

…then they divided by the key…

10 7 . 5 8 7 , 4 . 6 9 12

… and finally subtracted the key to reveal…

5 2 . 0 3 2 , -1 . 1 4 7

… which when entered into Scribblemaps revealed the secret location as Brackley.



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