5. Codebreaking

In this how-to episode, we talk about Codebreaking, with Steve, Dan, and Codemaster Cole. Codebreaking is an important skill, even if you're just trying to understand your baby sister, and even if this episode can't help you much with that, it will hopefully help you to find little things in letters. Plus, hear a thrilling mystery about an unbroken code. Oh, and could you tell a friend about the show? It would be a big help.

Here are the links from the episode:
Crack the Code
Explorer Academy Codebreaking Activity Adventure

The background music used in this episode is Bio Unit, Moving Sun, Apex, Zone, Pummel, Disco Tokyo, and Lonely Satellite, all by Bio Unit, and our theme song is Mosquito by Caspar Babypants.

 You can find Dr. Gareth's work at drgarethmoore.com. He has released many puzzle and cipher related books for kids, as well as a lot of stuff for adults, too. 

Thank you for listening.

Transcript

Barnabas  01:42
Welcome to the Kids' Code Podcast. I'm Barnabas, your host, and today we will be talking about codebreaking. Codemaster Cole, Steve, and Dan are in the studio with me. If you want to find out what the enemy is doing, you will want to be able to be able to break codes. If you're not a professional spy (like me and everyone else I know), codebreaking is still a good puzzle-solving skill. So, let's get into how to crack codes with these procedures from Top Secret by Paul B. Janeczko.

Barnabas  02:25
To start, you need some tools. The most important one is probably a frequency chart, a sheet of paper with the alphabet written along the left side. Depending on the length of messages you receive and the size of your paper, you might be able to write another alphabet in the middle of the page so that you can have 2 frequency charts from one piece of paper. You use the chart to count how many times each letter appears in the message. add a tick next to each letter you find. That is important because it tells you whether the message is a substitution cipher or a transposition cipher. A Substitution cipher is a cipher in which each letter is substituted for another letter, symbol, or word. A Transposition cipher is a cipher in which either the letters are mixed up in some way or there are letters added in (for example, Null ciphers have nulls). You will also need a plaintext alphabet, a strip of paper with the alphabet across it. You write letters in the cipher that you figure out below the English letter. I'll be back to these later. Finally, you need a frequency list. This would include most frequently used letters, least frequently used letters, and likely some other things, like most frequently used 2, 3, and 4 letter words, most used first and last letters, and most common double letters. The most common letters in English are E, T, A, O, N, I, S, R, H, and L. The least frequently used are Z, J, Q, X, K, V, and G. So, if the message has lots of Es, Ts, As, and Os, it's probably a Transposition cipher, but if there are a lot of Vs, Zs, Xs, and Hs, it's probably a Substitution cipher. Remember, though, that many messages, especially shot ones, will not have this exact frequency.

Steve  04:55
Yeah, like one message he cracked that had more Ts than Es.

Barnabas  05:01
It's interesting to note that frequencies from some other languages are similar to those in English. Here are some examples:

• Spanish: E, A, O, S, N.
• French: E, N, I, R, S.
• German: E, A, I, S, T.
• Italian: E, A, I, O, N.

Looking at those examples, you can see that in all of these languages, E is the most common letter, just like in English. Also, German is the only language of these that has T in the top 5 letters. And it's only number 5.

Steve  05:48
I also noticed that I is number 3 in French, German and Italian, and that S is in the top 5 for Spanish, French, and German, but they are 6 and 7 in English, respectively.

Barnabas  06:04
It can be fun to find these things, but it's also a good skill for codebreaking. For example, it will be easier to find double letters that appear multiple times. Here are some more frequency lists. Dan, could you help us with them?

• Most frequently used 2-letter words: Of, to, in, it.

Dan  06:31

• Most frequently used 3-letter words: The, and, for, are.
• Most frequently used 4-letter words: That, with, have, this.

Barnabas  06:48

• Most frequently used first letters: T, O, A, W, B, C.

Barnabas  06:55
Here is the process of cracking a code, starting with this message. Write it down if you want to go along with this procedure: DRO WKZ SC SX NKXQOB. WOOD DRO QXOXD DYNKI KD DGY SX PGYXD YP CDYBO. LO BOKNI DY VOKFO. Now it's time to crack the code. Codemaster Cole is checking a frequency chart. Keep in mind that E, T, A, O, and N are the most common letters in English. I think that Codemaster Cole is done. If think that you figured it out too, you can pause the episode and shout it to the person nearest to you.

Steve  08:13
Unless, of course, that person is your baby sister.

Barnabas  08:18
Right. Codemaster Cole, what did you find?

Codemaster Cole  08:22
That it has to be a Substitution cipher. O appears 11 times, D appears 10 times, and K appears 7 times, but E, T, and A don't appear at all.

Barnabas  08:38
Yes. Though O, the 4th most common letter in English, appears the most, it doesn't matter as much as T or E. Here, E could be O or D, but probably not K, Because it appears 4 times less than O. For our first guess, we'll say that O equals E and D equals T. Breaking a substitution cipher includes a lot of guessing, but you end up with a deciphered message. Now, put in E for O and T for D and look for common letters or words.
This is were the frequency list comes in. Look at the message and you frequency list and see if there are any clear words. There are three things I see. First, the three letter cipher word DRO, which appears twice in the message, includes D and O, which we think are really T and E. THE is the most common in English, so even though it could be TIE or TOE, THE makes the most sense, so let's add two Hes for two Rs. Second, we've guessed that the last three letters of the first word of the second sentence are e,e, and t. There are only a few words that end in eet. Feet and beet don't seem to fit, but meet works. So, I will add two ms for the two ws in the message. Third, we know that the first letter of the third word of the last sentence is probably T. The only common two letter word that starts with T is to, so Y is probably O. Now we have 11 Es, 10 Ts, 6 Os, 2 Hs, and 2 Ms.
Now, take another look at the message to see if the new letters show something else. I see something! Look at DGY in the second sentence. We know that D and Y are T and O, W is the only letter in English (other than a repeated O) so G must be W.
Now we should take a risk and see if it is correct, marking K, the third most common letter in the message, as A, the third most common letter in English. This gives us AT, the fifth word in the second sentence,

Barnabas  22:48
Steve and Dan are shadowing the Evil Ant. They followed him past stores, past houses, past the fire station and police station. They never got farther away from him, but they never got closer to him either. It was very frustrating. Then, the Evil Ant suddenly turned down an alleyway out of sight. They tried to follow him, but couldn't find him anywhere. Nowhere they looked could they find him. Not on a front porch, not behind the Bakery, nowhere. Then, Steve found a small piece of paper lying on the road. He picked it up. It had a coded message on it. They went back to their headquarters and reported all of this to Codemaster Cole, and they started trying to break the code. First, they checked it on a frequency chart. The most common letters were O and D. I won't go into the details, but Steve figured out the message, and it was:

Evil Ant  19:46
The map is in danger. Meet me in front of the store. Be ready to leave.

Barnabas  20:00
They realized that the Evil Ant was going to meet with Dangerous Dave in front of the department store. Then, Steve, Dan, Codemaster Cole, and Caw the Crow went off to spy near the store. After a little while, they saw Evil Ant came, and then, a little while after that, Dangerous Dave came up. The Evil Ant gave Dangerous Dave 2 papers and said

Evil Ant  21:02
Our next bank-robbing job is Tuesday.

Barnabas  21:11
Then, Dangerous Dave said

Dangerous Dave  21:17
Meet you there. and left.

Steve  21:22
Okay. Now we know the time of their next robbery, but we don't know the location.

Codemaster Cole  21:32
That's what we need to find out.

Barnabas  21:37
When the Evil Ant left the store, they started following him. Meanwhile, at the prison, Emily End had escaped! The jail guards hadn't seen anything, and the police were completely baffled. How did Emily End escape?