Lab 1: Message Decryptor

Problem 0 - Breaking the Interstellar Ice

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's your favorite constellation or asterism?
• If you had the capability to live on a planet other than earth, which planet would it be?
• If you were sent into space on Musk's Tesla Roadster, what three items would you bring to survive your mission?

Problem 1 - Cracking Encryptors

You are on a top-secret space force mission and need to send encrypted messages back to earth. 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-2021.arr", "10E2ySl2Kbp29om_HPisqojQZbiLU68WU") 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.
3. BONUS: Can you crack encryptor9 and encryptor10?

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Problem 2 - New Encryptor Swap

Oh no – you just received word that evil aliens broke your encryption scheme! It's up to you to create new encryption functions for your machine.

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 trade links (the second link that you are given after you publish, it should include import as) with another group and try to crack each other's encryptors. Use the same format that you used to import support.arr – call over a TA if you get stuck.

If you're having trouble with import

• 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

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.

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CHECKPOINT:

Call over a TA once both groups have solved each other's encryptors.

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Problem 3 - Encrypting Numbers

After building such a great encryptor, you realize that you forgot something! Your encryptor deals with Strings, but it doesn't disguise or change sequences of Numbers. This could be important if you ever want to be covert and secure.

Similarly to Problem 2, write another encryptor function called new-number-encryptor. This function should take in a Number and produce some output. You may use any combination of functions from the Pyret Numbers library.

Just like with new-encryptor, press the “Publish” button in the Pyret Code Editor and trade links with another group to try to crack each other’s encryptors. Use the same format that you used to import support.arr – call over a TA if you get stuck.

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

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CHECKPOINT:

Call over a TA once both groups have solved each other's Number encryptors.

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Success!

Nice! Your new encryptor functions worked! You can send secure messages back to earth without worrying about any evil aliens listening in.