Unit
5.2
We are cryptographers
Cracking codes
1 About this unit
Software: Scratch 2.0, The Black Chamber (website)
Apps: Snap!, The Black Chamber in the web browser
(Safari)
Hardware: Laptop/desktop computers
Outcome: Morse and semaphore messages, encrypted and
decrypted messages in various ciphers
UNIT SUMMARY
The pupils learn more about communicating
information securely through an introduction to
cryptography (the science of keeping communication
and information secret). They investigate early methods
of communicating over distances, learn about two early
ciphers, and consider what makes a secure password.
CURRICULUM LINKS
Computing PoS
Use logical reasoning to explain how some simple
algorithms work and to detect and correct errors in
algorithms and programs.
Understand computer networks including the
internet; how they can provide multiple services,
such as the world wide web; and the opportunities
they offer for communication and collaboration.
Use technology safely, respectfully and
responsibly; recognise acceptable/unacceptable
behaviour; identify a range of ways to report
concerns about content and contact.
Suggested subject links
Maths: Encryption and decryption use
mathematical functions. Frequency tables play a
role in cracking substitution ciphers.
History: There are interesting stories involving the
use of cryptography throughout history.
PSHE: Privacy, safety and identity can link to
topics in the school PSHE curriculum.
D&T and science: The pupils could make simple
electrical telegraph circuits.
TRANSLATING THE COMPUTING PoS
22
Computer networks, including the internet, are
not secure. To reduce the risks of this when using
the internet for communication and collaboration,
data is often encrypted – stored in a secret code.
While these systems are complex, the pupils can
gain some understanding by looking at earlier
systems. These will enable the pupils to develop an
understanding of how some algorithms work.
The security of personal information online is
often based on the use of passwords. Many
web-based services now demand that passwords
meet minimum complexity standards (although
this provides no protection when users choose to
tell others their passwords!). Keeping passwords
secure is an essential aspect of using technology
safely and responsibly.
LEARNING EXPECTATIONS
This unit will enable the children to:
be familiar with semaphore and Morse code
understand the need for private information to be
encrypted
encrypt and decrypt messages in simple ciphers
appreciate the need to use complex passwords
and to keep them secure
have some understanding of how encryption
works on the web.
The assessment guidance on page 30 will help
you to decide whether the children have met these
expectations.
VARIATIONS TO TRY
The pupils could investigate the historical contexts
in which cryptography and cryptanalysis have
developed and been applied.
The recommended resources could be replaced
or supplemented by using a spreadsheet or
programs in Python or Logo.
The pupils could study the way in which different
types of information, such as images and sounds,
can be digitised by computers.
2
Getting ready
THINGS TO DO
Read the Core steps sections of Running the task.
Decide which software/tools are most accessible/
appropriate for use with your class.
Download your chosen software/tools (see Useful
links) and spend some time familiarising yourself
with them.
Watch the Software in 60 seconds walkthrough for
this unit.
Think about the individuals and groups you have in
your class. Could you use any of the Extensions on
pages 24–29 to extend your more able children?
Could you use any of the suggestions in Inclusion
CD-ROM RESOURCES
Software in 60 seconds – Introduction to Snap!
Scratch cryptography scripts for pupils and
teachers (see Steps 2–5)
Semaphore reference sheet
Morse code reference sheet
Cipher template
Unit poster – Can you crack the codes?
(The answers to the codes are in Steps 1–3.)
List of prime numbers
Semaphore flag template
Pupil self-assessment information
E-SAFETY
The pupils will be making use of the web
throughout the unit, so the usual precautions over
online access should be in place.
If the pupils upload work they create for others
to see, make sure precautions are in place
to protect their identity, contact details and
intellectual property.
One of the key messages in the unit is the need
for password security. The pupils should
understand that they should not share passwords
with anyone else.
The unit also introduces the pupils to the use and
importance of encrypted internet connections.
Check with your network manager whether the
integrity of encrypted (HTTPS) connections is
observed by the school and its service provider.
INCLUSION
As with other programming work, aspects of this
unit make considerable intellectual demands
on the pupils. Some pupils may need additional
(see below) to support children with specific
needs, e.g. SEN or EAL? Have you considered
how a Teaching Assistant will support you and the
children, if one is available?
Ensure you have sufficient computers/laptops/
tablets and other equipment booked in advance.
If you will be going off site for this work, make the
necessary arrangements.
THINGS YOU NEED
Two flags per pupil
Torches
Electrical circuit equipment (optional): light bulb,
long wires, batteries and battery holder, crocodile
clips, switch
support and encouragement.
There are language packs built in to Scratch to
support pupils for whom English is a second
language. The statistical properties of other
languages differ from English.
The unit calls for attention to detail when working
with text, and some pupils might find additional
support useful for this.
WWW
USEFUL LINKS
Software and tools
Scratch is free software available to use without
registration: http://scratch.mit.edu.
Snap! is free open source software. Use online at
http://snap.berkeley.edu/snapsource/snap.html.
The example scripts used in the unit are at
http://scratch.mit.edu/projects/11939624 and
on the CD-ROM; you and your pupils are free to
modify these. A collection of cryptography function
blocks for Snap! are online at http://snap.berkeley.
edu/snapsource/snap.html#present:Username=mg
berry&ProjectName=crypto.
Simon Singh’s ‘The Black Chamber’:
www.simonsingh.net/The_Black_Chamber/
chamberguide.html.
Online tutorials
Introduction to Scratch 2.0: http://scratch.mit.edu/
help/videos.
Videos on cryptography: http://simonsingh.
net/media/online-videos/cryptography/ and
www.youtube.com/watch?v=EtYOXDr7u_E.
Information and ideas
Simon Singh has further resources available
online, as well as a curated collection of links; see
http://simonsingh.net/cryptography/crypto-links.
Further teaching materials, produced in association
with Bletchley Park’s National Code Centre:
www.cimt.plymouth.ac.uk/resources/codes.
23
24
3
Running the task – We are cryptographers
Software: Scratch 2.0, The Black Chamber (website) Apps: Snap!, The Black Chamber in the web browser (Safari) Hardware: Laptop/desktop computers
Outcome: Morse and semaphore messages, encrypted and decrypted messages in various ciphers
Core steps
Step 1: Transmitting information in semaphore
RESOURCES
Semaphore reference sheet
Unit poster reverse – Can you crack
the codes?
WWW
Semaphore interactive worksheet:
www.cimt.plymouth.ac.uk/resources/
topical/semaphore/semaphore.htm
POSSIBLE OUTCOME FOR THIS STEP:
Ask the pupils how people communicated over long
distances before the telephone and internet were invented.
What if they wanted to communicate as quickly as possible?
Introduce the pupils to semaphore, in which messages are
communicated by breaking them down into individual letters
and sending each letter over line-of-sight distances by using
a simple flag code. Give out the flags and the semaphore
reference sheet, assign pupils to partners and ask them to
practise sending and receiving messages in semaphore.
Ask them to decode the semaphore on the unit poster. (The
answer is: The smallest bone in your body is in your ear.)
Ask the pupils how they might use semaphore to communicate
over longer distances where the communicators cannot see
each other. Prompt them to think of a sequence of semaphore
signallers copying down messages and then passing them
onto the next in the chain. Attempt to send at least one
message like this. It’s helpful to have at least two pupils at
each point in the chain; one to receive, the other to send.
Note that it’s possible to pass the message on letter by letter
rather than waiting for the whole message.
Make connections between the way messages are transmitted
using semaphore and how internet routers pass on data
packets. See Step 2 from Unit 3.4 – We are network engineers.
Extensions
SCHOOL
Encourage the pupils to learn more
about semaphore signalling lines. A
good place to start is http://en.wikipedia.
org/wiki/Semaphore_line.
HOME
Ask the pupils to complete the interactive
exercise on semaphore at www.cimt.
plymouth.ac.uk/resources/topical/
semaphore/semaphore.htm.
Step 2: Using Morse code
RESOURCES
Morse code reference sheet
Unit poster reverse – Can you crack
the codes?
WWW
Morse code translator:
http://morsecode.scphillips.com/
jtranslator.html
Letter count tool: http://scratch.mit.
edu/projects/11939624/
POSSIBLE OUTCOME FOR THIS STEP:
SCHOOL
Assign the pupils a partner, and hand out a torch to each pair.
Challenge the pupils to work out how they can use the torch to
pass a message to their partner, and then compare solutions.
Introduce the pupils to Morse code, explaining that this is a
binary code (a code that uses only two symbols, in this case
on and off), in which each letter is represented by a particular
sequence of short or long pulses of light or sound, separated
by gaps.
Give out the Morse code reference sheet and ask the pupils
to practise sending and receiving messages using Morse code
over line-of-sight distances using a torch. Can they decode
the Morse code message on the unit poster? (The answer is:
A hippopotamus can run faster than a man.) Ask the pupils
to compare Morse code to semaphore. Which did they find
easier to use?
Ask the pupils to suggest why some letters, such as E and T,
have short codes, but others, such as Q, Y and Z, have longer
codes. Explain that some letters of the alphabet are much
more common in English than others, and Samuel Morse
designed the code to be as efficient as possible by assigning
the shortest codes to the commonest letters.
Ask the pupils how Morse code could be used over longer
distances. The pupils may suggest a similar receive and
resend method as with semaphore. Ask them about other
possibilities. Suggest that the torch could be modified, using
a long cable between the switch and the bulb.
Demonstrate this by connecting a light bulb to a battery and a
switch via long wires. Give the pupils time to experiment with
sending and receiving messages when one partner is out of
sight of the other.
Again, draw parallels with the internet, emphasising that on/
off electrical signals form the basis of communication at the
hardware level, although the code is different from Morse’s.
The pupils could create tally charts for
short passages from books of their
choice, to analyse how often each letter
occurs, or use the letter count tool in the
Scratch project at http://scratch.mit.edu/
projects/11939624/.
Some pupils could become proficient
at Morse using the practice machine
at http://boyslife.org/games/onlinegames/575/morse-code-machine/.
HOME
You could ask the pupils to research the
history of the electrical telegraph. A good
starting point is http://en.wikipedia.org/
wiki/Electric_telegraph.
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26
Core steps
Step 3: Using the Caesar cipher to create and crack codes
RESOURCES
Cipher template
Unit poster reverse – Can you crack
the codes?
WWW
Scripts for pupils: http://scratch.mit.
edu/projects/11939624/
Scripts for teachers: http://scratch.
mit.edu/projects/18994340/
Caesar cipher tool: www.simonsingh.
net/The_Black_Chamber/caesar.html
POSSIBLE OUTCOME FOR THIS STEP:
Ask the pupils how they might transmit a secret message
using semaphore or Morse code. Explain that they could agree
a cipher with their recipient in which, say, each letter of the
message was shifted one place along the alphabet. So ‘hello’
would be transmitted as IFMMP. Give the pupils time to send
messages to one another. Can they decode the message on
the unit poster? (The answer is: The word dinosaur comes
from the Greek language and means terrible lizard.)
Show the pupils the encrypt script in the Scratch project (see
Resources). Give them time to work out what each part of the
script does. (Comments are provided on this code.) Show how
the Scratch script can be changed to use a different Caesar
cipher by shifting the alphabet along a different number of
places. (Note that the cipher alphabet ends with a space.)
Give the pupils a chance to explore the Caesar cipher tool
at The Black Chamber (see Resources). Then give them
a message encoded in a Caesar cipher with an unknown
shift, e.g. P WXVW-FJPAXIN RDBEJIXCV TSJRPIXDC
TFJXEH EJEXAH ID JHT RDBEJIPIXDCPA IWXCZXCV PCS
RGTPIXKXIN ID JCSTGHIPCS PCS RWPCVT IWT LDGAS.
(The message reads: ‘A high-quality computing education
equips pupils to use computational thinking and creativity
to understand and change the world.’ The cipher used is a
shift of 15 places, from a to P, b to Q, etc.) Once a pair are
successful, ask them to explain the algorithm they used to
decrypt the message (e.g. repeatedly changing the number
of places they shift along the alphabet by 1, and checking to
see if the message makes sense).
Encourage the pupils to encrypt further messages using
the Caesar cipher, challenging their partner to decrypt them
without knowing the key, i.e. how far along the alphabet the
letters are shifted.
Extensions
SCHOOL
Some pupils could explore the pigpen
cipher at www.simonsingh.net/The_
Black_Chamber/pigpen.html. This is
available as a font at www.fonts2u.com/
pigpen-regular.font.
HOME
The pupils might like to experiment
further with encrypting and decrypting
messages in Caesar ciphers with their
parents, carers or siblings.
Step 4: Substitution ciphers and frequency analysis
RESOURCES
WWW
Encryption, decryption and letter count
tools:
http://scratch.mit.edu/
projects/11939624
www.simonsingh.net/The_Black_
Chamber/monoalphabetic.html
www.simonsingh.net/The_Black_
Chamber/letterfrequencies.html
www.simonsingh.net/The_Black_
Chamber/substitutioncrackingtool.
html
POSSIBLE OUTCOME FOR THIS STEP:
Explain that the security of the Caesar cipher rests on
keeping the key secret (i.e. how far along the alphabet the
letters of the message are shifted) but that this is a weak
encryption system as it’s easy to test all the possibilities.
Brainstorm ideas for how this could be made more secure.
Explain that there’s no need for the cipher alphabet to be
kept in the same order. Demonstrate how to encode a
message by substituting letters in the plain text alphabet
for the letter in the corresponding position of a mixed-up
alphabet such as EPHUBNJTGAWCSZLVQDOXYKFIRM.
Start with a short phrase, e.g. ‘hello’ becomes TBCCL.
Show how the Scratch scripts in http://scratch.mit.
edu/projects/11939624/ can be used to create a random
substitution cipher by changing the cipher alphabet to a
random order. Show the pupils the equivalent tool at www.
simonsingh.net/The_Black_Chamber/monoalphabetic.html.
Give them time to create and use random substitution ciphers.
Ask the pupils to think about the security of this system.
Would it still be easy to test all the possible keys? (No, as
there are very many of them.) This system can be quite easily
broken, though, because some letters come up more often
than others in English, as do some words. Ask the pupils to
think of examples (such as the letters ‘e’, ‘t’ and ‘a’, and the
words ‘the’, ‘to’, ‘and’, ‘of’ and ‘a’).
Ask the pupils to look at the letter count script at http://
scratch.mit.edu/projects/11939624/ and explain how it
works. Demonstrate the equivalent tool at www.simonsingh.
net/The_Black_Chamber/letterfrequencies.html.
Demonstrate how to use letter frequencies and common
words to crack a substitution cipher, working through
an example with a randomly chosen cipher text and
key at www.simonsingh.net/The_Black_Chamber/
substitutioncrackingtool.html.
SCHOOL
Some pupils could use and crack the
Vigenère cipher. See www.simonsingh.
net/The_Black_Chamber/vigenere_
cipher.html and related pages.
HOME
The pupils could ask their parents or
carers to use The Black Chamber tools
to send them messages encrypted
using a random substitution cipher. The
pupils could then decrypt the messages
using The Black Chamber’s substitution
cracking tool.
27
28
Core steps
Step 5: Password security
RESOURCES
WWW
Password guessing scripts:
http://scratch.mit.edu/
projects/11939624
POSSIBLE OUTCOME FOR THIS STEP:
Extensions
SCHOOL
Ask the pupils to think about all of the web-based services
they use, and ask them for which of these they have a
password. Make clear that their passwords are often the only
way they can prove their identity to the web server they’re
using, and that if anyone else uses their password the web
server will assume it’s them using it.
Some pupils could explore the
mathematics of password complexity,
e.g. see http://en.wikipedia.org/wiki/
Password_strength, or work to improve
the password-guessing script in the
Scratch project.
Brainstorm some of the consequences that might follow if
someone else were to use their account.
Emphasise how important it is that they never tell anyone
their password for any web-based services. Ask the pupils
to suggest some of the ways in which someone might try to
persuade you to tell them a password. The pupils might like
to do a role-play in which one partner tries to persuade the
other to give up a (in this case fake) password.
Explain that a good password shouldn’t be easy to guess,
either by people or computers. Ask the pupils to experiment
with the password-guessing script in http://scratch.mit.edu/
projects/11939624, starting with three-, then four- and finally
five-letter passwords, noting how much longer the script
takes to find their password as the length goes up. Ask them
to use logical reasoning to explain how this script works.
Ask the pupils to think about ways in which they could make
passwords harder for people or computers to guess. Typical
approaches on the web include using symbols, numbers and
both upper and lower case letters. Another approach is to
use much longer passphrases, made up of, say, four random
words from the dictionary. Typically, these are easier to
remember and harder to guess. See http://xkcd.com/936/.
HOME
Ask the pupils to review their passwords
for any web-based services they use,
and to use complex passwords where
they are not already doing so.
Step 6: Security on the web
RESOURCES
List of prime numbers
Pupil self-assessment information
WWW
Simon Singh’s Science of Secrecy
episode ‘Going Public’ (in two parts):
www.youtube.com/watch?v=_
ZTWLAqYf9c and www.youtube.
com/watch?v=oR0_LPbWxe4
POSSIBLE OUTCOME FOR THIS STEP:
SCHOOL
Explain that there’s a problem with using really good
passwords on the web if they are transmitted openly between
the user’s computer and the web server via the internet, as
all the routers would be able to read the password. Ask the
pupils to think about ways round this problem.
Computer scientists have found a way around having to
agree the key to code in advance. Their method is a bit like
keeping the key, but sending a padlock, so that the other
person can lock a message in a box and send it back to you,
but only you have the key to unlock it.
The maths involves using prime numbers. Give the pupils
some pairs of primes to multiply, e.g. 31 × 13 or 29 × 11 (see
the CD-ROM for a list of some prime numbers). This should
be relatively easy. Next, ask the pupils to work out which two
primes were multiplied to make, e.g. 2993; this is likely to be
much more difficult (41 × 73).
Watch Simon Singh’s Science of Secrecy episode, ‘Going
Public’ (see Resources). Discuss the ideas in the programme.
The mathematics is beyond primary level, but there’s no need
for the pupils to understand the details of the algorithm.
Show the pupils the difference between how http:// and
https:// ages are shown in their web browser.
Show them how to check the security certificates of encrypted
web pages, and warn them that they should pay attention to
the warning messages their browser displays if it has doubts
about whether encrypted pages should be trusted.
Ask the pupils to look back over the unit and to summarise
what they’ve learned. Encourage them to discuss the extent
to which this will affect how they use the web.
Finally, the children should evaluate the success of their
work.
Some pupils could write a Scratch
program to do prime factorisation,
perhaps using lists.
HOME
The pupils could talk to their parents or
carers about the importance of using
(and checking) https:// when entering
passwords and personal information.
29
4 Assessment guidance
Use this page to assess the children’s computing knowledge and skills. You may wish to use these
statements in conjunction with the badges provided on the CD-ROM or community site and/or with your
own school policy for assessing work.
BADGE
ALL CHILDREN SHOULD BE ABLE TO:
Send and receive messages
using Morse
LOGICAL THINKER 2 LOGICAL THINKER 2 COMMUNICATOR
and semaphore
COMMUNICATOR
Encrypt and decrypt messages using
the
LOGICAL THINKER 2
Caesar and substitution ciphers
COMMUNICATOR
Recognise the importance of keeping
CONTENT CREATOR 2CONTENT CREATOR 2
passwords entirely secret
E-SAFETY 2
Recognise the need for encryption when
LOGICAL THINKER 2 CONTENT CREATOR 2COMMUNICATOR
using the web
COMPUTING PoS REFERENCE
PROGRAMMER 2
Understand
opportunities for
PROGRAMMER 2 PROBLEM SOLVER 2 PROBLEM SOLVER 2
communication
Understand
networks
and the
PROGRAMMER 2
PROBLEM SOLVER 2
opportunities they offer for
communication
E-SAFETY 2
E-SAFETY 2
Use
technology safely and responsibly
SEARCHER
SEARCHER
Understand how the internet can
PROGRAMMER 2
PROBLEM SOLVER 2
SEARCHER
provide the world wide web
MOST CHILDREN WILL BE ABLE TO:
Send and receive messages
using Morse
LOGICAL THINKER 2 LOGICAL THINKER 2 COMMUNICATOR
CONTENT CREATOR 2COMMUNICATOR
and semaphore beyond line-of-sight
PROGRAMMER 2
E-SAFETY 2
Decrypt messages using
the Caesar cipher
LOGICAL THINKER 2 LOGICAL THINKER 2 COMMUNICATOR
with an unknown key
PROGRAMMER 2
COMMUNICATOR
Understand
opportunities
for
SOLVER 2 PROBLEM SOLVER 2
PROGRAMMER 2 PROBLEM
SEARCHER
communication
Understand
networks and the
PROGRAMMER 2 PROBLEM SOLVER 2 PROBLEM SOLVER 2
opportunities they offer for
communication
Recognise the importance of using
complex
CONTENT CREATOR 2CONTENT CREATOR 2
passwords
E-SAFETY 2
E-SAFETY 2
Use
technology safely and responsibly
SEARCHER
Understand how to check if a web
page is
CONTENT CREATOR 2CONTENT CREATOR 2
encrypted
E-SAFETY 2
E-SAFETY 2
Use
technology safely and responsibly
SEARCHER
SEARCHER
SEARCHER
SOME CHILDREN WILL BE ABLE TO:
Compare and contrast Morse and
LOGICAL THINKER 2
semaphore with the internet
Explain the algorithm for
the Caesar cipherCOMMUNICATOR
LOGICAL THINKER 2
Understand
computer
networks
PROGRAMMER 2
PROBLEM SOLVER 2
including the internet
COMMUNICATOR
LOGICAL THINKER 2 PROGRAMMER 2
Decrypt messages using
a THINKER
general
LOGICAL
2 LOGICAL THINKER 2 COMMUNICATOR
COMMUNICATOR
substitution cipher with an unknown key
CONTENT CREATOR 2
using frequency analysis
Understand what constitutes a complex
CONTENT CREATOR 2
password
E-SAFETY 2
Understand how to check the security
CONTENT CREATOR 2CONTENT CREATOR 2
certificates for a web page
E-SAFETY 2
PROGRAMMER 2
E-SAFETY 2
Use logical
reasoning
to explain
how PROBLEM SOLVER 2
PROBLEM
SOLVER 2 PROGRAMMER
2
some simple algorithms work
COMMUNICATOR
Understand
networks and the
PROGRAMMER 2 PROBLEM SOLVER 2 PROBLEM SOLVER 2
opportunities they offer for
SEARCHER
communication
Use technology safely and responsibly
CONTENT CREATOR 2 SEARCHER
E-SAFETY 2
E-SAFETY 2
Use
technology safely and responsibly
SEARCHER
SEARCHER
PROGRESSION
The following units will allow your children to develop their knowledge and skills further.
Unit
Unit
30
5.4 – We are web developers
6.1 – We are app planners
SEARCHER
5 Classroom ideas
Practical suggestions to bring this unit alive!
DISPLAYS AND ACTIVITIES
Morse and semaphore messages, as well as
encrypted and decrypted messages using a range
of ciphers, could make an interesting classroom
display.
Signalling in semaphore and Morse code is best
done away from the computer lab, either outdoors
or in the school hall.
There’s scope for circle time activities around
broader issues of privacy and identity.
Role-play is an effective approach to exploring,
and building resilience against, some of the ‘social
engineering hacks’ through which malicious
people attempt to obtain passwords.
WWW
WEBLINKS
One of the US’s leading experts on cyber security:
www.schneier.com/.
How one brand of internet firewall provides
decryption of HTTPS traffic: www.paloaltonetworks.
com/resources/demos/controlling-ssl-and-ssh.html.
CS Unplugged resources and links on
cryptography: http://csunplugged.org/
cryptographic-protocols.
This Royal Institution Christmas Lecture from 2008
includes some information about cryptography:
http://richannel.org/christmas-lectures/2008/2008chris-bishop-/christmas-lectures-2008-chrisbishop--untangling-the-web.
Google’s guide to online safety and security:
www.google.co.uk/intl/en/goodtoknow/.
The Cyber Security Challenge, sponsored by
GCHQ: https://cybersecuritychallenge.org.uk/
school-competitions.php.
Southampton’s National Cipher Challenge:
www.cipher.maths.soton.ac.uk.
Materials on cyber security for schools from the
US NSA: www.nsa.gov/kids/.
VISITS
It’s hard to beat a trip to Bletchley Park near
Milton Keynes for this unit – there are details of the
education programme at www.bletchleypark.org.
uk/edu/pgm.rhtm.
Bletchley Park is also home to The National
Museum of Computing, which is a separate
organisation with its own education programme.
See www.tnmoc.org/learn/educational-visits.
BOOKS
Gardner, M. Codes, Ciphers and Secret Writing.
(Dover Publications Inc, 2003)
Hodges, A. Alan Turing: The Enigma. (Vintage, 1992)
Newman, D. Top Secret Code Book.
(Macmillan Children’s Books, 2012)
Petzold, C. Code. (Microsoft Press, 2000)
Singh, S. The Code Book. (Fourth Estate, 2002)
Standage, T. The Victorian Internet.
(Bloomsbury Publishing, 2014)
6 Taking it further
When you’ve finished, you might want to extend the project in the following ways.
Cryptography and cyber security are huge topics.
There’s further material that pupils could explore
independently on The Black Chamber site and
elsewhere. See Useful links on page 23 and
Weblinks on this page for some suggestions.
The cryptographic work by Alan Turing, Tommy
Flowers and others at Bletchley Park in World War II
was of great significance in British history and in the
history of computing. The Bletchley Park website
(see Weblinks) is one starting point for finding out
more about this. For those in schools with NEN
internet connections, www.hoc.lgfl.net provides a
useful resource on the history of computing.
The pupils might like to explore some of the press
coverage over alleged routine monitoring by the
NSA and GCHQ of internet communications, e.g.
via www.theguardian.com/world/prism.
Broader issues around online rights and security
might be worth discussing. The US Electronic
Frontier Foundation (www.eff.org) and Open
Rights Group (www.openrightsgroup.org) are
active pressure groups in this area.
The pupils could explore steganography (the study
of hiding information).
31