Lab 1: Message Decryptor

Problem 0 - Get to know each other!

Welcome to CSCI 0111 Lab! We're so excited to work with you. Now that you're with your partner(s), discuss one/some/all of these questions:

• What is your favorite food?
• What's the last song you listened to?
• What do you do for fun?

Problem 1 - Following Steps

Exchange your program-steps.pdf from Homework 1 with your partner's. Follow their written steps to create the image they had in mind.

Once both of you have finished creating the images, compare them to the program-image file that it was supposed to look like.

What was challenging about creating an image from written steps vs. the visual reference?

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CHECKPOINT:

Call a TA over to discuss the question above and show them your images!

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Problem 2 - Cracking Encryptors

You're on a top secret mission and need to communicate an encrypted message containing important code. However, the instructions to your encryption machine were accidentally thrown out, and it’s up to you to figure out how it works!

The encryptor machine has 10 black-box functions that encrypt a String. Your first task is to test various inputs and figure out how each function changes the input based on the output.

Once you have an idea of what an encryption function does, write a version of the function that encrypts a String in the same manner and run it through the checks in the support file. If all checks pass, then you’ve successfully built an encryptor for covert communications!

Instructions

Include this at the top of your program:
import shared-gdrive("lab1-support-2022.arr", "1kS_-rd0eE9-DLndIYw-0Bez8c6J73MRK") as support

Now you will be able to access all of the encryptors and their testers in your Pyret file.

The encryptor functions are named

support.encryptor1,
support.encryptor2,
support.encryptor3,
support.encryptor4,
...
support.encryptor10

The encryptor functions take in Strings as input (e.g: support.encryptor1("mystery")) and produce an encrypted result.

Please keep a record of what Strings you use to test each encryptor – you should be prepared to explain your choice of Strings to a TA. They will be useful for you to reference, too!

The tester functions are named, inspiringly:

support.test-encryptor1,
support.test-encryptor2,
support.test-encryptor3,
support.test-encryptor4,
...
support.test-encryptor10

To use them, you must use the name of your function as an input. For example, after giving some inputs to support.encryptor1, you may think it always returns the String "cs0111" (HINT: it doesn't do this – just an example). Then you would write the function:

​fun my-cool-encryptor(str :: String) -> String:
​    "cs0111"
end

You would test whether your function is correct (meaning it does the same thing as encryptor1 for all inputs) by running:

​support.test-encryptor1(my-cool-encryptor)

Hint: The encryptors are composed of functions from the Pyret Strings library. Start by reading through it.
Hint: When choosing Strings to use as inputs to the encryptors, it will be useful to vary your inputs – think about why this could be. In what ways can you vary your Strings?

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CHECKPOINT:

1. Call over a TA after you have finished encryptors 1-4
2. Call over a TA after you have finished encryptors 5-8.

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Problem 3 - New Encryptor Swap

Oh no – the previous encryptions have been compromised! It's up to you to create new encryption functions which can't be decoded as easily.

Instructions

In a new document, write an encryptor function. Call it new-encryptor. It must take in a single String and produce some output. You may use any combination of functions from the Pyret Strings library to build your function.

Once you're done, press the "Publish" button in the Pyret Code Editor and copy the import statement (the second link that you are given after you publish, it should include import as) into this spreadsheet in an empty row in the "Problem 3" section.

Important considerations for proper imports

• Make sure that you have provide * and provide-types * at the top of your file before you share code with the other team
• Be sure to save your files

Now it's time to prove your encryptor expertise - let's solve the final two encryptors in the support code, support.encryptor9 and support.encryptor10.

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CHECKPOINT:

Call over a TA once you have finished encryptors 9-10.

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Now that you're an encryptor expert, try cracking someone else's encryptor!

Task: Import another group's encryptor from the encryptor swap spreadsheet using the same format you used to import support.arr – call over a TA if you get stuck.

Task: Write a function called new-decryptor that takes in the output of the other group's new-encryptor and decrypts it. When you think your decryptor works, consult with the other group.

Success!

Nice! Your new encryptor functions worked! You successfully sent the code and the mission was completed.