CRYPTOGRAPHY FOR MIDDLE SCHOOL STUDENTS IN
AN EXTRACURRICULAR LEARNING PLACE
Nadine Bergner, Jan Holz and Ulrik Schroeder
Computer-Supported Learning Research Group, RWTH Aachen, Ahornstr. 55, Aachen, Germany
Keywords: Extracurricular Learning Place, Course Design, Learning Methodologies, Blended Learning, Collaborative
Learning.
Abstract: In order to inspire middle school students for computer science topics we developed a two-day-course about
cryptography. Thereby we try to counteract the relatively low interest in STEM (science, technology,
engineering and mathematics) topics by offering engaging insights into computer science. This course is one
of several workshops within our extracurricular learning place for computer science called InfoSphere. The
fundamental idea of the presented workshop is to provide a first insight into the world of cryptography for
middle school students. During the course groups of three to five students discover the four different
cryptographic methods Skytale, Fleißner Template, Caesar Encryption and Vigenère Encryption on their
own. We designed the course according to the didactic principle of exploratory learning, so the participants
can learn action-oriented and at their individual learning rate. In conclusion we discuss the results of a first
evaluation with a test group of 23 students (17 girls and six boys).
1 INTRODUCTION
Now and in the future Germany, like many other
countries, has the problem of having too few well
educated computer scientists. One reason for this is
the low interest in STEM (science, technology,
engineering and mathematics) among school
students. We try to counteract this by offering
engaging insights into computer science for school
students. The presented course is one of several
workshops within our extracurricular learning place
for computer science called InfoSphere. These
courses are developed to motivate children to get in
contact with computer science topics.
We chose the topic cryptography, because it is
not included in regular school lessons, but is suitable
to show that computer science has to offer much
more than just programming. This is part of our
overall goal to convey an idea about computer
science which is as realistic as possible. Furthermore
we particularly aim at addressing girls and students
who are generally less interested or less promoted in
STEM topics, as can be seen within our project
IGaDtools4MINT. We try to motivate especially
these target groups by discussing security aspects
with a strong link to the students’ everyday lives
(e.g. login on websites like Facebook).
The cryptography workshop is designed as a
two-day-workshop for twelve to twenty participants
at the age of eleven to fourteen. The course itself can
be visited by heterogeneous groups with students of
different ages, so that they can benefit from each
other because of their different prior knowledge.
The participants work in four parallel groups of
three to five students and they develop the different
tasks and puzzles step-by-step on their own. We
created various hands-on learning materials to
address as many senses as possible and manage the
whole course without classical worksheets. Our
inspiration comes from Janette Griffin: "[...]
important features of programs which engender
long-term learning and interest are: planning;
consideration of the unique learning opportunities of
the institution rather than mirroring school-type use;
variation in the activities during the visit; sparing
use of worksheets; and emphasis on first-hand
experience and observation." (Griffin, 1994, S. 121)
Within this concept the students are able to learn
at their own speed, which is a very important
didactical advantage (see Aepkers et al., 2002). To
support an individual learning rate, a specifically
developed software program leads the students
through the course step by step. To continue within
265
Bergner N., Holz J. and Schroeder U..
CRYPTOGRAPHY FOR MIDDLE SCHOOL STUDENTS IN AN EXTRACURRICULAR LEARNING PLACE.
DOI: 10.5220/0003920002650270
In Proceedings of the 4th International Conference on Computer Supported Education (CSEDU-2012), pages 265-270
ISBN: 978-989-8565-07-5
Copyright
c
2012 SCITEPRESS (Science and Technology Publications, Lda.)
the program the students have to understand each
cryptographic method and give correct answers to
corresponding questions. Therefore it is unnecessary
to control the students at any time.
We will start with explaining the idea of the
extracurricular learning place for computer science
called InfoSphere. After this we give an overview
about the cryptography course with our motivation,
the main idea and the structure of the two-day-
workshop. Section 3 describes the workshop in
detail and gives an insight in the used learning
materials. Afterwards we summarize the results of
the first test run with a group of 23 middle school
students. Thereby we report our impressions and the
feedback of the participants, resulting in an outlook
on our future work. Closing up Section 6 gives a
final summary.
2 INFOSPHERE - AN
EXTRACURRICULAR
LEARNING PLACE FOR
STUDENTS OF ALL AGES
An extracurricular learning place serves to teach
specific topics of one field to students of different
ages. The InfoSphere is an extracurricular learning
place especially for computer science topics. It
opened in summer 2010 under the leadership of the
Computer-Supported Learning Research Group of
the RWTH Aachen University (see Lehr- und
Forschungsgebiet Informatik 9). The InfoSphere
offers several perspectives on numerous facets and
applications of computer science for students of all
ages and types of school beginning with class three.
The InfoSphere provides courses as an addition
to regular school lessons. In Germany, North Rhine-
Westphalia there are no obligatory computer science
lessons in school. This is the reason why many
students do not get in contact with computer science
topics during K-12. This in turn leads to the problem
of many first-year students in computer science
having a wrong idea about computer science studies
(Heine, 2006); (Maass und Wiesner, 2006). High
dropout rates during the first semesters at university
are the result (Heublein et al., 2010). Besides
correcting the students’ idea of computer science
and encouraging interest in this field we try to
reduce these dropout rates by providing a publically
available extracurricular learning place.
For achieving this, the InfoSphere offers a wide
range of courses for half a day, a full day, or several
days. These courses provide experimental and
action-oriented learning with a link to the students’
everyday experiences. One of the essential features
of InfoSphere courses is the very individual access
they offer for the different topics. Combined with
self-directed learning and peer-teaching, this should
encourage school students to discover the various
aspects of computer science on their own. Our idea
is to enable a learning process that is as natural,
exciting and self-discovering as possible. By this
these courses should help to raise interest in
computer science even for those who are not tech-
savvy or did not get in contact with computer
science so far. Another motivation to open an
extracurricular place of learning was to assist
computer science teachers and students in teacher
training in teaching novel topics and becoming more
familiar with modern learning materials, methods
and media. InfoSphere has been designed as a
research laboratory to test and practice different
learning experiences. Moreover, it offers a plethora
of modern media and technology (e.g. multi touch
tables, smartphones and interactive whiteboards) to
help trainee teachers implement innovative learning
scenarios. Furthermore, students in teacher training
get the chance to acquire crucial media competences
in practice. For these reasons the courses are
designed by two to four students in teacher training
under supervision of the members of the teacher
training chair.
Within the InfoSphere we investigate the
following research questions.
• How can an extracurricular learning place like
InfoSphere help to convey a realistic picture of
computer science?
• What are the most significant criteria to change
the existing stereotypes about computer science?
• How can we correct the picture for different
target groups?
• What should a workshop look like to create this
picture as realistic as possible?
• What are the crucial differences between male
and female participants?
3 PROCEDURE OF THE
CRYPTOGRAPHY COURSE
At the beginning of the first day we start with a get-
to-know-round, because the students know neither
each other nor us. After this we randomly split the
participants into four groups. To increase motivation
we show each student group a treasure chest which
is locked and send them on a hunt for the right key.
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Afterwards each group gets a laptop and starts the
accompanying program. In the first step they can
choose one of four avatars, which lead them through
the program and a name for their group (see Figure
1: Screenshot of the intro screen).
Figure 1: Screenshot of the intro screen.
After this, Skytale is introduced as the first
cryptographic method (Hebisch 2010); (Kaul, 2006).
It is a very easy method, which was used by the
Spartans around fifth century BC. To encrypt a text
you have to wrap a small paper strip around a
wooden stick (see Figure 2: Skytale), write the text
horizontally on the paper strip and loose it from the
stick.
Figure 2: Skytale.
After this a foreign person cannot read the text
because the letters are disordered. To decode the text
the receiver has to know which diameter the stick
must have. Otherwise s/he has to try all possible
diameters of the stick until s/he can read the
message.
Instead of explaining the method to the students
we provide some wooden sticks and labelled paper
strips and let the students guess how this technique
works. The program requests two words from the
encrypted text to see if the group has decoded it
right. The supervisors keep themselves in the
background unless the students ask especially for
help. In these cases the supervisors give little hints
to help the students to find a solution on their own.
For detailed information about the didactical method
“discovery learning” see Aepkers (Aepkers et al.,
2002).
After every student has understood the way to
decode a text with the Skytale method, they have to
encode another text. Only when the group can en-
and decode a text with the Skytale method, the
program allows them to get to the next section.
The second cryptographic method the students
get to know is the Fleißner Template (see Brätz,
2010). This method exists since 1881 and needs only
a square paper template (see Figure 3: Fleißner
template). A specific restriction of this method is
that the text has to consist of 4, 16, 36 or 64 etc.
letters because of the 2x2, 4x4, 6x6 or 8x8 square. In
the following we use a 36 letter example. To encode
a text you have to write the first nine letters into the
gaps of the template from top to bottom and from
left to right. After that you have to rotate the
template clockwise by 90° and go on with the next
nine letters. Finally you have a square of 36 letters
which seems to be arranged in a random manner. To
decode such a square of letters the receiver has to
know how the Fleißner template has to look like,
that means where the gaps are. Otherwise s/he has to
try all possibilities for a 6x6 square with 9 gaps.
Figure 3: Fleißner template.
Similar to our procedure with the Skytale method
we give a Fleißner template and a paper with a
square of 36 letters to every group of students. The
program again requests the students to guess how
this method works. When they use the given
template in the right way they can read a simple
question. After entering the correct answer into the
program, it shows the students a new message,
which then should be encoded with the Fleißner
template. Only if the groups enter the decrypted
message in the program (see Figure 4: Screenshot of
the section Fleißner template) and shows that they
understand the de- and encryption with the Fleißner
template the program allows them to discover the
third cryptography method.
As a third method the students get in contact
with the Caesar Encryption (Freiermuth, 2010). This
method works with a shift of all letters by a defined
code letter in the alphabet. For example if you shift
every letter by the code letter “D”, you have to
replace an “A” by a “D”, a “B” by an “E” etc. To
simplify this process you can use a disk with two
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267
alphabets on it, so that you only have to rotate it to
the right position (see Figure 3: Caesar disc). After
this you can replace every original letter by the one
next to it on the disc. If the receiver does not know
the right code letter s/he has to try all 26 different
possibilities.
Figure 4: Screenshot of the section Fleißner template.
Figure 5: Caesar disc.
Like the two times before the groups get the
learning material and can check out the different
options on their own. In this case they get a text
where the first letters are already decrypted to give
them a hint how they have to turn the Caesar disc.
After the students have found out the right code
letter, they can decrypt the whole text without any
problems. The second step is to encrypt an answer
message to send it back. When the students solve
this task as well the program leads them to the last
cryptographic method.
The last introduced cryptographic method is the
Vigenère encryption (Freiermuth, 2010). This
method is an extension of the Caesar method, where
every letter is encrypted by a different Caesar shift.
That is the reason why you need not only one code
letter, which determines the shift, but a code word
(here for example “KEY”) so that each letter defines
a different shift. If you want to encrypt the letter “D”
as the first letter of your text, you have to use the
first letter of your code word “K” and therefore
replace the “D” by a “N” (see Figure 6: Screenshot
of the section Vigenère encryption).
Figure 6: Screenshot of the section Vigenère encryption.
When all four groups have finished the program,
each group gets the task to prepare a short
presentation about one of the four cryptographic
methods including its advantages and disadvantages.
In the following discussion round we talk about how
save each method is respectively how much effort is
necessary to crack the method. It is important not
only to know how the methods work but also for
which texts they are useful. Therefore they can take
pictures with digital cameras of themselves and the
material or produce short video films to explain the
different methods. The students are encouraged to
design a creative presentation, which they present to
the other participants, the supervisors and their
families. Furthermore we look out on computer
assisted methods, which can be developed in an
advanced workshop.
At the end of the workshop the students are able
to open the treasure chests from the beginning and
unpack the sweets, which is a great reward for them.
4 RESULTS AND FEEDBACK
First of all the list of participants with 23 students
(17 girls and 6 boys) on it shows that the topic
cryptography is popular among twelve to fifteen
year old students (the aimed maximal number of
participants was 20). It seems to be especially
interesting for girls. The rate of female to male
students (female: 73.9 % to male: 26.1%) is
extraordinary for a computer science workshop.
Mostly there are much more boys than girls in the
groups visiting us (34.1 % girls on average in 2011).
The overall outcome of our test run is that the
students’ learning rate is higher than expected. The
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participants completed the whole course in about 6
hours.
The course itself shows that it is very worthwhile
to design workshops with a lot of teamwork. It is
really remarkable how much the students learn from
each other and how little help of the supervisors is
needed. Also the students report back that it is (a lot
of) fun to work in groups (see Diagram 1:
Percentage values to: "It was fun to work in
groups.").
Diagram 1: Percentage values to: "It was fun to work in
groups."
Some of them say that it would be greater to
choose the groups on their own, but we intentionally
mix the groups so that everybody has the chance to
get to know new people. Otherwise it is very
difficult for single participants to get into contact
with an existing group. Besides this remark all
participant enjoyed it to work in groups.
As expected the four groups do not work at the
same speed because of the different ages and prior
knowledge. This fact was calculated in advance. So
we integrated special tasks and encourage the
students to help each other.
Additionally the evaluation shows that the course
motivates the majority of participants to follow up
other topics of computer science because they
experienced that computer science is really
interesting. Some students were very surprised that
computer science includes topics like cryptography
as well. To evaluate what students associate with the
term computer science we ask the students before
and after the course which three words they
associate with computer science. In both surveys the
most frequently mentioned answer was “computer”,
but in opposite to “programming”, “mathematics”,
“studies” and a list of programming languages
before the course, after the course some students
answer “cryptography”, “puzzles”, “problem
solving” and even “fun”. For detailed data see
Diagram 2: keywords before the course and Diagram
3: keywords after the course.
Diagram 2: Keywords before the course.
Diagram 3: Keywords after the course.
Diagram 4: Students’ ideas of computer science.
Furthermore we analyzed the student’s idea of
“computer science” in general. To figure out if the
cryptography course is able to change this idea a bit,
we consult the students before and after the course.
Diagram 4: students’ ideas of computer science
contrasts the results. This shows that the
cryptography course is able to change the students’
idea of computer science a little bit in short time, but
there is no evidence for a long lasting change. Our
assumption regarding long term changes is that it is
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269
helpful and necessary to offer multiple courses over
a longer time.
5 FUTURE WORK
On the basis of the test run we plan to expand the
course with a fifth cryptography method (Enigma
decryption). We are going to convey the history and
functionality of the Enigma. This would be an
additional part, which can be used flexible
depending on the learning group. Furthermore we
are going to develop an advanced cryptography
workshop about computer assisted methods.
Based on the limited space in front of the
laptops, we are going to reproduce all materials to
enable a group size of three.
Furthermore we aim to publish the materials on
our website, so that middle school teacher can use it
for their courses in school if they do not have the
possibility to visit the InfoSphere. However this
would mean a lot of preparatory work to build all the
hands-on materials.
In order to reach additional target groups we are
going to develop equivalent courses for other classes
with different computer science topics. Currently we
are working on courses for computer graphics in
class twelve and logical circuits in class eight.
6 CONCLUSIONS
Altogether the cryptography course is a great way to
reach out to those students, who are not yet excited
by computer science. Especially for girls teamwork
is very important. Apart from that female and male
students enjoy it to be creative in designing
presentations and like it to present their own work. It
is essential to present computer science to middle
school students in an interesting and exciting way,
because this is the time of life where most of them,
especially girls loose the interest in STEM topics.
Above all we are going to add this course to the
regular offering at our extracurricular learning place
for computer science topics InfoSphere.
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