Along with my friend and colleague Lucy Simko, I have been working on a an activity/interactive presentation themed around secret messages that is suited for a wide age range of students.
Secret message puzzle
We originally developed the activity for the CSE Computing Open House in December 2017.We used a different secret message themed activity developed with colleagues Anna, Ada, and others in a previous Open House, which is why some of the files I reference may have roman numeral II in their name.
The goals of this activity are:
- Expose students to basic concepts of encryption and simple ciphers
- Demonstrate that simple ciphers can be broken with frequency analysis
- Brainstorm (collectively) ways in which a cipher and/or message can be changed to create a stronger code (hopefully students will naturally come across concepts that have been used in cryptography)
In the Open House setting, middle and high school students and their parents wander around the CSE building at their own pace and stop into various booths or rooms for short periods to participate in activities. Activities need to be designed in a way that allow the students to dive into them mostly on their own and asynchronously with other students.
Materials for this activity are available:
Although the message solving aspects of the activity were successful in the Open House setting, we felt that the questions and deeper applications or connections of the activity would have been more interesting to discuss with a larger group of students in something closer to a classroom setting (like the Open House, students did not have access to computers for the activity).
We adapted the activity for a presentation during the UW GEAR UP Early Engineering Institute (to middle school students) in June 2018. With this new setting in mind, we added two additional goals for the activity:
- Highlight the significance of math in solving this puzzle
- Learn about the historical significance of secret messages, substitution ciphers, and frequency analysis
We further adapted the activity to be suitable for high school girls during a UW CSE Summer Camp for a group of high school girls participating in the Girls’ Creative Project group later in June 2018. For this group, we created an iPython Notebook version of the activity so that we could interactively solve the puzzle and test out the students’ brainstormed ideas for making the code or message more challenging.
The iPython/Jupyter Notebook is available on my Github page: here.
Unfortunately, Github doesn’t display the notebook as nicely as my local copy, but hopefully the idea is still clear (and if you are familiar with iPython/Jupyter notebooks, you can download and open it locally for a better view).
One of my favorite aspects of the iPython Notebook based version of this puzzle is the ability to use an online cryptogram solver and compare its performance on different versions of the puzzle. I think students will be surprised at what changes it is robust to and what changes cause it to fail. A summary of the cryptogram solver’s performance is included in the notebook and in the figure below.
Online cryptogram solver’s performance on variations of puzzle
The motivation for creating this secret message using symbols rather than an easier-to-type/write substitution cipher using just letters was to illustrate that for substitution ciphers (which includes caesar ciphers), the key (which letters are chosen to represent which other letters) is not particularly important in many cases.
Aspects of history brought up in our presentation included: (1) the origins of frequency analysis, which date back to 9th century studies of the Qur’an; (2) uses of ciphers and secret messages in war (particularly WWII), (3) anthropological uses of frequency analysis to guess the linguistic origins of unknown texts, and (4) the file compression properties that frequency analysis enables (for instance, Morse Code uses shorter sequences to encode more common letters and longer sequences for the least common letters).
Although we did not touch on these connections in our presentation, other school subjects such as Literature could also be incorporated into a lesson on secret messages and frequency analysis. Edgar Allan Poe’s poem “The Gold Bug,” for instance, contains a cryptogram that can be solved with frequency analysis.
A public version of the presentation slides is still under development and will be added soon.
Camille Cobb 