‘16-‘17 General Discussion for Lesson 4.5


Use this thread to discuss your questions and comments about how to run the lesson.


Does anyone have the codes text that students are supposed to get after they use the tool. I am struggling with getting the answer? Also, does anyone have a good explanation for the frequency relationship?



@jmclean I will check to see if there is a key to the encoded text. One of the encoded paragraphs is a song.

With frequency relationships, they should look for word or letter patterns. Since “e” is the most repeated letter in the alphabet, they can start with looking for letters that repeat. For example if they see a word “wyyt” the “yy” could be “ee” or oo.



Yeah, this is one level type where we (curriculum team) can’t show teacher-only answers - the feature is just not implemented.

I assume the random substitutions are what’s giving you trouble. Here is the key:

Title	    Answer                              First line
-------     --------------------------------    --------------------------
Sample 1    Hitchhiker's guide to the galaxy    Far out in the uncharted backwaters of the unfashionable..."
Sample 2    Aloe Black song                     Feeling my way through the darkness...
Sample 3    Gettysburg Address                  Four score and seven years ago...
Sample 4    I'm Happy Lyrics                    It might seem crazy what I'm about to say...
Sample 5    I Have a Dream speech               so even though we face...


Student Question: Why did you make the widget so that the frequencies don’t match up?


hey, @carmichaelc! the widget shows the frequency of letters across the whole english language with the blue bars, and the frequency of letters within the selected text in the orange bars, which is why they won’t match up perfectly. you can check out the frequency analysis technique in more detail, here.


Here is an answer that was given by a student to the following Reflection Question about Frequency Analysis: “Knowing what you know now about frequency analysis, would you feel comfortable sending your password over the Internet using a substitution cipher?”

Answer:Yes I would, because my password is not something like a full message, where words can be guessed based on patterns throughout the message. My password is normally just a certain arrangement of letters, so there would still be 26! different patterns one must try to make sense of the password, and even then one might not know whether it was my password or not.

Can anyone respond whether this is a valid response or was he not really answering the question?

Thanks, Jen


@jmclean that is a great question! I think as a teacher I would accept the answer - the student is thinking critically about the question/content and they address the frequency piece by saying that frequency would not make a difference in their password because of how their password is chosen.

That being said, I would also clarify with the student that we still want a stronger encryption method - I think the video in lesson 6 does a good job of explaining that. I think it is tricky for students to wrap their heads around how long it would take a computer to solve some of these problems - it can be tricky for me! I think I would re-visit the response to this question after they do the asymmetric key lesson to show how much stronger public key encryption is. I am interested in what others think too though!


The “discussion question” at the beginning of the lesson was a great way to shift to encryption from Big Data. We talked about using “Pig Latin” when students were younger and other students who take ASL talked about signing as another way to communicate. Some students got stuck on “I don’t tell anyone” or “I talk to them quietly” as their answer, but overall it was a fun way to brainstorm and motivate the need for encrypting information. I was also sure to bring up the internet unit where we saw that anything could be read to connect it to previous learning.

This lesson ran a little short for me today so we has a little time to review the vocabulary from lesson 4.6 and apply it here right away.

I caught one student admitting that cracking the random substitution cipher was “fun” :slight_smile: Overall it was engaging for students. We even had a little time to talk about the difference in time it would take to crack these two codes, which, as a math teacher, I enjoyed!


Thank you. I did discuss that even though the password he created was strong, he should still not want to send his password over non-secure channels such as in an e-mail. I think his argument was if frequency analysis was the only method used it would be impossible to crack, which in this case would be true.


A colleague asked for a video showing a walk through of solving the random cipher. In case it’s helpful for anyone else, here it is: https://youtu.be/vf7VIB6xe5A?hd=1


One thing to note as well on breaking a random cipher is that the frequency tool shows you 2 things: the frequency of letter usage in the English language in general, and the frequency of letters used in the encrypted message. While this information can be very helpful in matching up what a letter has been changed to, it will not be a perfect process since the encrypted message is not an exact representation of the entire English language. For example, the phrase “Zebras love pizza” is very short, and a “z” turns out to be the most commonly used letter. This would be misleading, but we must remember that a very short message is less likely to reflect the general commonalities of English letter usage.

So the tool (widget in this case) gives us guidance, but it is not a perfect system, so we still rely on logical conclusions like starting with small words (1 or 2 letters) like in the video linked above. As we crack those small words, the longer words will hopefully become easier (again looking for words where we are only missing 1 or 2 letters after the update).