Week 7 Studio: Secret Message
Git Repository: https://classroom50.org/lis875/lis-875-f26/assignments/secret-message/accept
For today’s studio, I am going to give you a secret message. The secret message has been scrambled; your goal is to figure out what the message says. OR, more accurately, your goal is to write a program to help you figure out what the message says.
Here is the message:
hnronxttfao fi x lrnt rl knbxvfdb bphnbiifra.
hnronxttfao fi x vrrz, tske zfqb xa xnvfiv unsie rn x vd kxtbnx.
fv kraivnxfai gexv yrs kxa cr knbxvfdbzy,
usv xzir knbxvbi txay abg rhhrnvsafvfbi lrn favbnxkvfdb bphnbiifra.
In this message, each letter has been replaced with a different letter. So, for example, I might have replaced every a with a q, and every e with a z. (That’s not the actual replacements.) You need to figure out the key: what letters are replacing what other letters?
You could do this by hand. You could manually replace one letter with another, and see if it works. And keep track of whether it works. OR, you could automate this: you could try to program the computer to guess every combination of letter replacements to see which one works. Which will take the computer a long time – and it’ll be tough for the computer to know whether it got the right answer.
By far, the best way to do this is half-way between these two options: write a program to work with a user (you) to make guesses.
You should write a guessing program. The guessing program should ask the user for a letter in the message, and then a letter to replace it with, and then print out the message with the letters replaced. This way, the user (who will also be you) can see the message so far, along with your guesses. This way, you can make guesses, and the computer can do the tedious work of replacing letters and keeping track of old guesses.
I like to have the message printed in lower case letters, and any guessed letters replaced with upper case. So, for example, your output might look something like this:
Current Message: abcd cd f ghddfjh
What letter do you want to replace? a
What letter do you want to replace it with? T
Current Message: Tbcd cd f ghddfjh
What letter do you want to replace? b
What letter do you want to replace it with? H
Current Message: THcd cd f ghddfjh
What letter do you want to replace? c
What letter do you want to replace it with? I
Current Message: THId Id f ghddfjh
What letter do you want to replace? d
What letter do you want to replace it with? S
Current Message: THIS IS f ghSSfjh
What letter do you want to replace? f
What letter do you want to replace it with?
Your goal today is to write a program so that you can work with the computer to figure out the secret message above. Work in teams of 2-4 people to figure out the secret message.
Note: For TODAY, you are not allowed to use ChatGPT, Copilot, or other generative AI programs. The goal of this studio is to think about ways that you can program computers to work with humans to solve problems better than they can alone. Learning this may help you think about how generative AI can be used.
That’s it. That’s the whole of the instructions – form a group, write the guessing program, and then use the program to guess the message. Have fun with it.
What follows is just advice for doing it. You don’t have to follow my advice. Do whatever you want. This is just my experience in doing this, and you might want to do it differently.
Advice
Start simple, and build
The first thing to do is to get the program written. Start simple. Write a program that prints out the message. Run it to make sure it works. Then ask the user for a letter, and a new letter to replace it with. Store them in variables, and print them back out. Run it to make sure it works. Then add in the replacements, and make sure that works. Then put it in a loop so the user can make more than one guess.
Slowly add features to your program until it has all the things you need it do. Remember, the goal is to make an interactive program that will help you figure out the secret message. The program doesn’t figure it out itself; instead, it should support and help you to figure it out.
Multi-line Strings
The secret message is more than one line long. Normally, strings in python have to fit on one line: "hello". To put a multi-line string in your program, use triple double-quotes around it, like we did in Tuesday’s lab:
message = """
hnronxttfao fi x lrnt rl knbxvfdb bphnbiifra.
hnronxttfao fi x vrrz, tske zfqb xa xnvfiv unsie rn x vd kxtbnx.
"""
Replace
Python has a nice .replace() function that enables you to replace one letter (or substring) with another. It then returns the new string. So
original = "food for the guest"
new_thing = original.replace("g", "Q")
print(new_thing)
prints out
food for the Quest
If the replacement string appears more than once, then the .replace() function replaces all instances.
Use Case to your Advantage
The entire message right now is in lowercase letters. Use that to your advantage. When you replace a letter, replace it with a capital letter. That way, you can tell which letters are original, and which have been guessed. That’s what I did in the example above; as I guessed letters, I replaced the original, lowercase letters with the newly guessed capital letter.
One way to do this is to manually type in lower case letters and upper case letters when you are a user running the program. That will work! But it is hard to remember, and really really confusing if you don’t get it right.
You can make the program a bit easier to use by having the program automatically convert input from the user into lowercase or uppercase as appropriate. In python, if you have a string variable, you can convert it to uppercase with the .upper() function, and to lowercase with the .lower() function. (If the letter(s) are already uppercase and you ask for uppercase, then it doesn’t do anything.)
Count Letters
How do you know what letters to guess? Well, in the English language, some letters (like e) appear much more often than other letters (like q).
To help you guess, you could write a separate program that counts letters. Ask the user for a letter, and then count how many times it appears in the message. Remember – you are writing the program. You can write a second program easily – just open up a new file and start writing! You’ve done this before.
Once you have a program that counts how many times a letter appears, you can use it to help you. What letter is most common? Print out the frequency of each letter in the message. Then you can compare that to the frequency of letters in the English language to try to guess what letters replaced what other letters. For example, in English, the letter ‘e’ is the most common letter. In the message, what is most common? Guess that that is an ‘e’…
Hint: You can use a for loop to loop through the letters in a string.
for letter in message:
print(letter)
Hint 2: You can also check if the letter is the one entered by the user:
if letter == letter_from_user:
count = count + 1
Guess
Puzzles like these are called cryptograms. There is advice on the Internet to help you solve them.
Start Over
As a user of the program, sometimes your guesses will be wrong, and you will decide you are going down the wrong path. When that happens, you’ll want to start over. The easiest way to start over is to stop the program, and then run it again. Add some way to exit the program. For example, if instead of typing in a letter, you type “quit”, then it can exit the program. OR, if you just hit enter instead of typing in a letter, maybe it will exit the program.
Hint: The command sys.exit() allows you to quit the program. To use that command, you have to put the instruction import sys at the top of your python file.
Challenge: More Messages
Here are a couple of more messages. Use your program to help you figure out each of these messages. Note that each message uses a different key.
Message #1:
ymrov srk, pj ia jmt-vm-edihxk mqpjpmj, mdr imvt pjkcesdvtphxk vmdrwk mf islpw.
wsqshxk mf hmte pjfxpwtpjl pjbdra, sjo rkikoapjl pt.
― sxhdv odihxkomrk,
Message #2:
pdyn hjqm je ojqjhmi, ed idf'h gsehm jh ojxjfb edqmdfm moem'e ojcm.
idf'h vm hnsuumi vp idbqs – gljal je ojxjfb gjhl hlm nmeyohe dc dhlmn umduom'e hljfzjfb.
- ehmxm wdve
Message #3:
syk qnyg is qxjk iakd zjj, syk qnyg is bnyp iakd,
syk qnyg is wqnyg iakd zjj, zyp ny iak pzqrykff wnyp iakd
Extra Challenge
Write a program that will encode secret messages. It should ask the user for a (possibly multiple line long) message. Then it should randomly create a key, encode the message, and print out both the encoded message and the key.