EECS 183 Project 3: Ciphers

Direct autograder link

Overview

In this project, you will move on to cryptography and you’ll be asked to encrypt and decrypt messages using three different encryption algorithms. The S’more part of this project will challenge you to “crack” others’ secret messages in ciphertext and convert them back to plaintext. Assignment Writing Service

Objectives

• To have fun.
• To practice loops.
• To gain experience with strings.
• To become better acquainted with functions and libraries.
• To allow you to dabble in cryptography.

WARNING: Beware the autograder’s ability to detect cheating, see Honor Code for further information. Assignment Writing Service

Honor Code

Collaboration Policy and the Honor Code

You are encouraged to:

• Give or receive help in understanding course concepts covered in lecture or lab.
• Practice and study with other students to prepare for assessments or exams.
• Consult with other students to better understand project specifications.
• Discuss general design principles or ideas as they relate to projects.
• Help others understand compiler errors or how to debug parts of their code

The following are considered Honor Code violations:

• Submitting others’ work as your own.
• Copying or deriving portions of your code from others’ solutions.
• Collaborating to write your code so that your solutions are identifiably similar.
• Sharing your code with others to use as a resource when writing their code.
• Receiving help from others to write your code.
• Sharing test cases with others if they are turned in as part of your solution.
• Sharing your code in any way, including making it publicly available in any form (e.g. a public GitHub repository or personal website).

The full collaboration policy can be found in the syllabus. Assignment Writing Service

Remember that we grade your BEST submission for style. If multiple submissions are tied in score, we take the last of those. Assignment Writing Service

Starter Files

Download the starter files using this link. After unzipping, you’ll find these files: Assignment Writing Service

utility.h A header file with declarations (aka prototypes) of the helper functions you’ll have to implement. Assignment Writing Service

utility.cpp Implementations of functions declared in utility.h. Assignment Writing Service

caesar.h A header file with declarations of the functions related to caesar cipher you’ll have to implement. Assignment Writing Service

caesar.cpp Implementations of functions declared in caesar.h. Assignment Writing Service

vigenere.h A header file with declarations of the functions related to vigenere cipher you’ll have to implement. Assignment Writing Service

vigenere.cpp Implementations of functions declared in vigenere.h. Assignment Writing Service

polybius.h A header file with declarations of the functions related to polybius cipher you’ll have to implement. Assignment Writing Service

polybius.cpp Implementations of functions declared in polybius.h. Assignment Writing Service

ciphers.cpp A function that allows the user to encrypt and decrypt messages. This file uses functions from utility.h, caesar.h, vigenere.h, polybius.h. Assignment Writing Service

start.cpp A program that allows you to select between executing your tests in test.cpp and using the ciphers you have created. Assignment Writing Service

Additionally, you’ll be working with this file that you’ll have to create yourself: Assignment Writing Service

test.cpp A test suite for functions declared in utility.h, caesar.h, vigenere.h, polybius.h. Its job is to reveal bugs that someone (e.g. you or staff) could have made while implementing those functions. All testing should be done by printing to the standard output. Note that there will be no main function in this file. Assignment Writing Service

NOTE: The starter code will not compile until you: Assignment Writing Service

• Create a test.cpp file with a function named startTests(). Your project will not compile until you have created your test.cpp. More details can be found in the section Creating test.cpp.

Suggested Timeline

As an approximate timeline, you will be on track if by: Assignment Writing Service

• September 30: Starter code downloaded and new project set up in IDE. All necessary file(s) created. Code compiles on your IDE. Code compiles on the autograder (submit to verify). You’ve read through the spec.
• October 4: Functions in utility.cpp implemented, fully tested, and passed on the autograder. Associated testing functions in test.cpp implemented, working, and catching the associated bugs on the autograder. Suggested order: toUpperCase(), removeNonAlphas(), charToInt(), removeDuplicate().
• October 9: Functions in caesar.cpp implemented, fully tested, and passed on the autograder. Associated testing functions 
• October 15: ciphers() and all other code should be completed. Debugging in progress. Passing all individual function tests, 80% or higher on autograder.
• October 16: Last day to still get 5% extra credit for your project 3 submission!
• October 18: Final due.
• If at any point your code is not working as intended checkout the troubleshooting checklist

Warm-up

To make working on this project easier and more fun, be sure you’re able to answer the following questions: Assignment Writing Service

• Recall our friend modulo, %. What does it do?
• What’s the difference between a char and a string?
• How can you figure out the length of a given string?
• Suppose you have a variable of type string called word, and that word is of some positive length.
  • Without knowing word’s length in advance, how could you print its first character?
  • How about the last character?
  • How would you print word’s nth character?
• How can you represent an empty string, i.e. a string of length 0?

• Suppose you somehow ended up with this code: Assignment Writing Service

  	string firstName = "Julius";
  	string lastName = "Caesar";
  	// ...

  and that you’d like to have another string, fullName that would join (i.e. concatenate) firstName and lastName, so as to get "Julius Caesar". How best to do this? Assignment Writing Service

• Surf on over to http://www.asciitable.com and make note of Dec and Char columns.
  • Recall from lecture that characters, such as letters, punctuation marks and digits are represented by a number in the computer. So to store the character A, the computer is really storing the number 65. Similarly it stores 97 to represent a. Because of this property, you can increment chars and do arithmetic with them just like you can with ints.
    • Note You should never refer to ASCII values when working with chars. Instead, always use the alphanumeric or symbol representation. For example

    	// do NOT use numerical ASCII values in your code, like below
    	char ch = 65;
    	if (ch == 66) {
    	....
    	}
    	// Instead, use the alphanumeric representation, like below
    	char ch = 'A';
    	if (ch == 'B') {
    	....
    	}

  • What is the value of character at the end of this code’s execution? Assignment Writing Service

    	char character = 'A';
    	character += 1;
    	character += 'A' - 'a';
  • How would you print all the letters in the alphabet, A through Z, with just a couple lines of code (without hardcoding all those letters)?
• What’s the difference between 0 and '0'?
• How can you determine if a character is a lowercase letter?
• How can you determine if a character is an uppercase letter?
• How can you determine if a character is alphanumeric or alphabetical?

Getting Started

Multiple Files

• Most programs in the real world are written in more than just one file, to break down the functionality into smaller parts and to keep the program’s organization clean. Assignment Writing Service

• For Projects 1 and 2, you worked with just one file, such as rps.cpp. It had a main() function, where the execution began, and then some other functions that were called from main() or from other functions. But as a program gets more complicated, the file becomes longer and it becomes difficult to organize and test the program. Assignment Writing Service

• Then the program will contain one other .cpp file (without a header file) that will contain a main function that drives the program. This .cpp file will #include any header files that contain the definition of any functions that it might need.
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Creating a Project

• In the Distribution Code you’ll find utility.h, caesar.h, vigenere.h, and polybius.h that has declarations for some functions. You’ll also find caesar.cpp, vigenere.cpp, polybius.cpp, and utility.cpp whose job is to implement those functions. You will also find ciphers.cpp which is the driver that makes use of the ciphers you have implemented. Finally, there is a file start.cpp which contains the main() function for the project. This function will allow you to select executing your test cases or using the ciphers you have written.As usual, the code in start.cpp will print the project menu with options to either run the tests in test.cpp or call driver function for the project, ciphers(). Enter 1 to select executing your test cases starting with the startTests() function in test.cpp, enter 2 to select executing your ciphers starting with the ciphers() function in ciphers.cpp. test_toUpperCase(), your program might run as follows (bold text represents your input): Assignment Writing Service

• To begin, create a new project in Xcode or in Visual Studio and add caesar.h, vigenere.h, polybius.h, utility.h, caesar.cpp, vigenere.cpp, polybius.cpp, utility.cpp, and ciphers.cpp to your project. Be sure that the files are copied and stored in the project directory. Assignment Writing Service

  WARNING: When adding files to your project, be sure that the files are copied and stored in the project directory! Assignment Writing Service

Test Suite

Creating test.cpp

• As you write code, it’s important to test it! Catching and fixing bugs early is much easier than later on; this will save you hours when you work. So you’ll be required to create and submit a test suite for this project. Assignment Writing Service

  NOTE: The best practice is to write tests before even implementing functions. Writing tests will make implementing the function faster/easier, PLUS it is infinitely satisfying to be able to test a function immediately once you’ve implemented it. Assignment Writing Service

• Create a new file and call it test.cpp. At the top of the file, put a multiline comment with the project’s name, your name and uniqname, your partner’s name and uniqname, if you have one, and a short description for this test file. This file will in fact test the functions declared in utility.h, caesar.h, vigenere.h, and polybius.h so be sure to add these lines: Assignment Writing Service

  	#include "utility.h"
  	#include "caesar.h"
  	#include "vigenere.h"
  	#include "polybius.h"

  after the multiline comment. Note that the filename is enclosed in double quotes "" and not angle brackets <>, which means that it’s a local file and not a system library. Assignment Writing Service

  WARNING: Make sure that it’s #include "utility.h". Don’t #include "utility.cpp". Assignment Writing Service

  NOTE: If you’re using Xcode and it gave you main.cpp with a main function, you won’t need it! So be sure to delete it. Or just rename main.cpp (from Xcode) to test.cpp; this way you don’t have to create a new file. Assignment Writing Service

• Next, write a startTests function in test.cpp. This file will test functions declared in utility.h, caesar.h, vigenere.h, and polybius.h via standard output, so you’ll be calling those functions many times. Here’s a good way to start it: Assignment Writing Service

  	#include "utility.h"
  	#include "caesar.h"
  	#include "vigenere.h"
  	#include "polybius.h"
  	#include <iostream>
  	#include <string>
  	using namespace std;
  	void testShiftAlphaCharacter();
  	void startTests() {
  	testShiftAlphaCharacter();
  	// Repeat for all other functions to be tested
  	return;
  	}
  	void testShiftAlphaCharacter() {
  	cout << "Now testing function ShiftAlphaCharacter()" << endl;
  	cout << "Expected: 'a', Actual: '" << shiftAlphaCharacter('a', 0) << "'" << endl;
  	cout << "Expected: 'b', Actual: '" << shiftAlphaCharacter('a', 1) << "'" << endl;
  	cout << "Expected: 'd', Actual: '" << shiftAlphaCharacter('b', 2) << "'" << endl;
  	return;
  	}

• shiftAlphaCharacter does not print anything, it just returns a character. If you were to just call this function, nothing would be printed to the console. But shiftAlphaCharacter does return a char. And so in order to check the correctness of this function’s implementation, you have to print its return value. Assignment Writing Service

• When you test these functions, you may wish to pay close attention to the Requires clause of each function. For example, the Requires clause for shiftAlphaCharacter functions “requires” that c is an alphabetical character. This means that you can assume that this function will always receive an argument that is an alphabetical character. Furthermore, you should not be calling it from the test suite with a value that violates the Requires clause. Doing so will cause your test suite to fail the autograder. For example, don’t call shiftAlphaCharacter with an argument of '@'. Assignment Writing Service

  WARNING: If you submit a test case that violates the Requires clause, we will stop grading that submission and you will receive a very low score. Assignment Writing Service

• As you work on the functions in utility.cpp, you should write some test cases first, then write the implementation, and then run the program to check if the implementation is correct. You should repeat this with functions in caesar.cpp, vigenere.cpp, and polybius.cpp. Assignment Writing Service

List of Functions to Test

Here the a list of functions you will need to test in test.cpp. Assignment Writing Service

• toUpperCase()
• removeNonAlphas()
• removeDuplicate()
• charToInt()
• shiftAlphaCharacter()
• caesarCipher()
• vigenereCipher()
• fillGrid()
• mixKey()
• findInGrid()
• polybiusSquare()

Submit Frequently

• As you progress through the project, we encourage you to submit after completing each section of the project. Doing so will help to ensure that you have written each part correctly before moving onto building the next. Assignment Writing Service

• When you submit test.cpp, we will compile and run it with our correct implementation of utility.cpp, caesar.cpp, vigenere.cpp, and polybius.cpp and with our buggy implementation of utility.cpp, caesar.cpp, vigenere.cpp, and polybius.cpp so as to generate two different outputs. We will then compare two outputs. If there is any difference, you’ve successfully exposed a bug! The autograder does not go into the details of what the difference is, it only sees if there exists a difference. Assignment Writing Service

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• Remember that some functions do not print anything on their own; we have to print their return value, as with the function shiftAlphaCharacter(): Assignment Writing Service

  	cout << shiftAlphaCharacter('a', 0) << endl;
  	cout << shiftAlphaCharacter('b', 2) << endl;
  	cout << shiftAlphaCharacter('X', 5) << endl;
  	cout << shiftAlphaCharacter('X', 50) << endl;

• After you submit your test suite, you might see output that looks like this: Assignment Writing Service

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  That means that your test suite exposed 1 out of th 13 bugs in the staff’s “buggy” implementations of the project and your score for the test suite is 0.9 out of 10 points. The total points you can earn on test.cpp is capped at 10 points. You do not need to find all of the bugs to receive all of the points. Assignment Writing Service

Bugs To Expose

There are a total of 13 unique bugs to find in our implementations. Your tests do not need to expose all of the bugs to receive full points for the project. The autograder will tell you the names of the bugs that you have exposed, from the following set: Assignment Writing Service

• CAESAR_SHIFTALPHACHARACTER1
• CAESAR_SHIFTALPHACHARACTER2
• CAESARCIPHER
• UTILITY_CHARTOINT
• UTILITY_REMOVEDUPLICATE
• UTILITY_REMOVENONALPHAS1
• UTILITY_TOUPPERCASE
• POLYBIUS_FILLGRID
• POLYBIUS_FINDINGRID
• POLYBIUS_MIXKEY
• POLYBIUSSQUARE
• UTILITY_CHARTOINT
• UTILITY_REMOVEDUPLICATE
• UTILITY_REMOVENONALPHAS2
• UTILITY_TOUPPERCASE
• VIGENERECIPHER

Helper functions

After your code compiles, your next task in this project is to indulge in writing functions in utility.cpp. These functions will serve as helper functions in caesar.cpp, vigenere.cpp, and polybius.cpp Remember to write your testing function for each function before you write the function itself. For example, write test_toUppercase() (in test.cpp) before you write the implementation of toUpperCase(). Assignment Writing Service

toUpperCase()

• This function converts all alphabetical characters in the string original to uppercase. Assignment Writing Service

• As an example of how this function works, suppose in test.cpp you call it and print its return value like this: Assignment Writing Service

  cout << toUpperCase("Diag @ 11 p.m.") << endl;

  Then the following should print: Assignment Writing Service

  DIAG @ 11 P.M.

removeNonAlphas()

• This function removes all non-alphabetical characters from the string original. Assignment Writing Service

• As an example of how this function works, suppose in test.cpp you call it and print its return value like this: Assignment Writing Service

  cout << removeNonAlphas("Diag @ 11 p.m.") << endl;

  Then the following should print: Assignment Writing Service

  Diagpm

removeDuplicate()

• This function removes all duplicate characters except the first occurrence of it from the string original. Assignment Writing Service

• As an example of how this function works, suppose in test.cpp you call it and print its return value like this: Assignment Writing Service

  cout << removeDuplicate("HELLOWORLD") << endl;

  Then the following should print: Assignment Writing Service

  HELOWRD

charToInt()

• This function converts the character original to its integer representation. Assignment Writing Service

• As an example of how this function works, suppose in test.cpp you call it and print its return value like this: Assignment Writing Service

  cout << charToInt('1') << endl;

  Then the following should print: Assignment Writing Service

  1

cctype Library Functions

You are allowed and encouraged to use functions from the cctype library shown in the Character operations section in zyBooks. Assignment Writing Service

WARNING: Do not compare boolean values to true or false in a conditional expression. Assignment Writing Service

When using these functions, the note below the table is critical in understanding how to use the functions like isalpha, isdigit, and isspace. As noted in zyBooks, for functions like isalpha, false is zero and true is non-zero. Assignment Writing Service

This means you must never do the following: Assignment Writing Service

if (isalpha(someCharVariable) == true) Assignment Writing Service

Instead you should do something like this: Assignment Writing Service

if (isalpha(someCharVariable)) Assignment Writing Service

to_string Function

You may find the function to_string helpful in this project. The function takes as input an integer (it also works for double but that is not relevant for this project), and returns a string with characters of text representation of the integer input. Note this does not work to convert a char to a string. Assignment Writing Service

Ciphers

IMPORTANT: As you implement the functions in the next section, you will find it helpful to refer to the Function Table linked at the bottom of the spec. The table contains the relationship between the functions below, i.e., which functions are called by others. Assignment Writing Service

Art of Cryptography

• This type of “art” deals with scrambling information, so that passwords, credit cards and other sensitive data are all the more secure. An example with which you might already be somewhat familiar is HTTPS, a secure version of HTTP (a protocol that web browsers use to communicate with servers). When a browser requests a webpage from a server via HTTPS (and the address of that webpage will begin with https://), all the data flowing between the browser and the server is encrypted (i.e. converted into seemingly meaningless characters). This is useful for logging into websites like Facebook, for credit card purchases on online stores such as Amazon, and especially so for accessing account information on banks’ websites.

caesar.cpp

Cæsar

• History holds that Julius Caesar protected sensitive messages by “rotating” each letter by 3 positions, so A became D, B became E, …​, Z became C: Assignment Writing Service

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• This type of cipher is know as a substitution cipher, i.e. each letter is substituted with another. In the case of Caesar’s cipher, we have a secret key that’s known only by those who are supposed to know the information that is shared. This secret key (k) is used to rotate (i.e. shift) each letter by k places, wrapping A to Z and a to z as needed. Assignment Writing Service

• For example, suppose that the secret key is 10 and the plaintext message is Meet me at the Diag at 11 p.m. We would encrypt this message by shifting each letter 10 places: Assignment Writing Service

  	Meet me at the Diag at 11 p.m.
  	Wood wo kd dro Nskq kd 11 z.w.

  Notice how M became W, since W is 10 characters away from M. Similarly, t became d. t is the 20th letter in the alphabet (and the English alphabet has just 26 letters), so after we get to z (26th letter), we go back to a and go through three more letters to find d. Assignment Writing Service

• Some additional notes: Assignment Writing Service

  • A negative key would shift the letters back. So if the key were -3, E would become B and A would become X. Assignment Writing Service

  • Because the English alphabet has just 26 letters, keys of -25, 1, 27, 53, etc. are equivalent. Assignment Writing Service

  • This cipher will encrypt only uppercase and lowercase letters. This means that only alphabetical characters are shifted. Furthermore, uppercase letters will remain uppercase and lowercase letters will remain lowercase after shifting. All other characters will remain the same. Assignment Writing Service

  • Decrypting Caesar cipher is fairly simple: it suffices to shift the letters the other way. Assignment Writing Service

• For more information (and history), check out http://en.wikipedia.org/wiki/Caesar_cipher. Assignment Writing Service

NOTE: Most of this project’s specification has been encrypted with a key of 26, which is twice as secure as a key of 13.[1] Assignment Writing Service

• And now, an overview of functions that you must implement in caesar.cpp. Note that the functions that follow do not print anything on its own; instead they return the result.

shiftAlphaCharacter()

• This function “requires” that the first argument that’s passed in, c, be a letter. So you may assume that it will only be called with an uppercase or a lowercase letter. And remember not to call this function with anything but alphabetical characters, not even in your test suite! Assignment Writing Service

• Shifting a character is illustrated by the same diagram you saw earlier. Suppose that you’re working with uppercase characters and n is 3. Then the characters would be shifted like this: Assignment Writing Service

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• Note that the letter must remain in the same case after you shift it. So if c is lowercase, it will remain lowercase when this function returns it; if c is uppercase, it will remain uppercase. Assignment Writing Service

• And this is how you can test shiftAlphaCharacter in test.cpp. Since the function itself does not print anything, we have to print its return value: Assignment Writing Service

  	cout << shiftAlphaCharacter('a', 0) << endl;
  	cout << shiftAlphaCharacter('b', 2) << endl;
  	cout << shiftAlphaCharacter('X', 5) << endl;
  	cout << shiftAlphaCharacter('X', 50) << endl;

  You should get this output: Assignment Writing Service

  	a
  	d
  	C
  	V

caesarCipher()

• As its name suggests, this function encrypts or decrypts the string that’s passed in using the algorithm described above. Assignment Writing Service

• For example, suppose original is the string "Meet me at the Diag at 11 p.m.", key is 42 and encrypt is true. Then calling caesarCipher and printing its return value in test.cpp Assignment Writing Service

  cout << caesarCipher("Meet me at the Diag at 11 p.m.", 42, true) << endl;

  would cause the following to be printed: Assignment Writing Service

  Cuuj cu qj jxu Tyqw qj 11 f.c.

  To decrypt a message, call caesarCipher with encrypt set to false: Assignment Writing Service

  cout << caesarCipher("Cuuj cu qj jxu Tyqw qj 11 f.c.", 42, false) << endl;

  which would print Assignment Writing Service

  Meet me at the Diag at 11 p.m.

IMPORTANT: Don’t forget to keep writing tests in test.cpp for functions we declared in caesar.h! Assignment Writing Service

For creating and verifying test cases for your caesarCipher, this website may be helpful. Assignment Writing Service

vigenere.cpp

Vigenère

• As you might imagine, Caesar cipher is not all that strong, since it only takes to go through at most 25 different keys to break it. (Interested in breaking the Caesar cipher? Check out this project’s S’more!) For this reason, the world (or the French?) came up with Vigenère cipher. It dates to the fifteenth century and is one of the truly great breakthroughs in the development of cryptography. For more information, check out http://en.wikipedia.org/wiki/Vigenère_cipher. Assignment Writing Service

• Vigenère cipher improves upon Caesar cipher by shifting letters using different keys. This sequence of keys is known as a keyword. Each letter in the keyword represents by how far the corresponding letter in the original message will be shifted (A and a represent 0, B and b represent 1, Z and z represent 25). Assignment Writing Service

• For example, suppose you still want to send that same secret message, Meet me at the Diag at 11 p.m. But this time, you’re more careful and are using Vigenère cipher with the key Squirrel! Here’s how to encrypt: Assignment Writing Service

  	plaintext: Meet me at the Diag at 11 p.m.
  	key: SQUI RR EL SQU IRRE LS Q U
  	ciphertext: Euyb dv ee lxy Lzrk ll 11 f.g.

• We first converted each letter of the keyword to uppercase and removed all non-alphabetic characters. We also applied the key just to letters and repeated the keyword after its last letter. Since S is 18 characters away from A, M is shifted by 18. Assignment Writing Service

• So putting it all together, you will need to do the following: Assignment Writing Service

  • Convert all letters in the keyword to uppercase.
  • Remember to strip all non-alphabetic characters from the keyword.
  • The keyword can be of any length greater than 0 and repeats after its last character.
  • Apply the keyword only to alphabetical characters in the original message.
  • As in the Caesar cipher, Z wraps to A and z wraps to a.
  • Decrypting would shift the letters backward.
  • This cipher will encrypt and decrypt only uppercase and lowercase letters. This means that only alphabetic characters will be shifted. Furthermore, uppercase letters will remain uppercase and lowercase letters will remain lowercase after shifting. All other characters will remain the same.

vigenereCipher()

• Notice that this function “requires” that keyword contain at least one alphabetical character. This means that you every time you call this function the string you provide as the second argument needs to have at least one letter in it. Make sure this is true for you function calls when testing the function, as well as anywhere else in your code. Assignment Writing Service

• When you implement this function, be sure to follow the rules outlined above. Assignment Writing Service

• As an example of how this function works, suppose in test.cpp you try to encrypt the string "Meet me at the Diag at 11 p.m." with the keyword "Squirrel!" call it and print its return value like this: Assignment Writing Service

  cout << vigenereCipher("Meet me at the Diag at 11 p.m.", "Squirrel!", true) << endl;

  Then the following ciphertext should print: Assignment Writing Service

  Euyb dv ee lxy Lzrk ll 11 f.g.

  Remember that decrypting shifts the letters backward! As an example: Assignment Writing Service

  cout << vigenereCipher("Euyb dv ee lxy Lzrk ll 11 f.g.", "Squirrel!", false) << endl;

  And this is the output: Assignment Writing Service

  Meet me at the Diag at 11 p.m.

polybius.cpp

Polybius Square

• While shifting characters based on a key is common in ciphers, another common approach is to construct a grid as a cipher. As the name may suggest, the Polybius Square is a device invented by the Ancient Greek historian and scholar Polybius. Assignment Writing Service

• Although Polybius did not intend for his device to be used as a cipher, the Polybius Square is said to have been used in the form of the “knock code” to signal messages between cells in prisons by tapping the numbers on pipes or walls. Assignment Writing Service

• The original grid consists of the English alphabet and the digits 0 through 9. Assignment Writing Service

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  Each letter is then represented by its coordinates in the grid, with the row number first and then the column number. For example, "EECS" becomes "04040230" in the original grid above. Assignment Writing Service

• The encryption process using a Polybius Square begins with generating a Mixed Square, using a keyword. Once the Mixed Square is generated, we replace each letter with the “coordinates” of the letter within the grid, reading across first and then down (i.e. row and then column). Assignment Writing Service

• As an example, we shall encrypt the plaintext “EECS” with the keyword “POLYBIUS”. Assignment Writing Service

• First we make the Mixed Square using the keyword. We start by filling in the squares in the grid with the letters of the keyword, ignoring repetitions, and then continue with the rest of the alphanumerical letters in its original order. Assignment Writing Service

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• With the Square complete, we simply find each plaintext letter in the grid, and replace it with its coordinates. So “E” becomes “15”, “C” becomes “13”, and “S” becomes “11”. With this, we get the ciphertext “15151311”. Note that each alphanumeric character is always represented by a pair of digits. Assignment Writing Service

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• Decryption works in the reverse order, by translating the coordinates to its corresponding letter in the grid. Assignment Writing Service

• The Mixed square is generated in exactly the same way as we did before. Assignment Writing Service

• Imagine we received the ciphertext “435445” and the key is “POLYBIUS” again. Then “43” becomes “1”, “54” becomes “8”, and “45” becomes “3”. With this, we get the plaintext “183”. Assignment Writing Service

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IMPORTANT: Note that the grid does not represent any non-alphanumerical character. This means that such characters cannot be encrypted. However spaces are allowed in the plaintext, and should be represented as spaces in the ciphertext. Assignment Writing Service

fillGrid()

• Notice that this function “requires” that content be of length of 36. This means that you should never be passing a string that has a length that does not equal 36. Assignment Writing Service

• As an example of how this function works, suppose in test.cpp you try to fill the grid with the constant string ALNUM defined in utility.h. To test that your grid has been filled correctly, you should call the printGrid function implemented for you in utility.cpp. Assignment Writing Service

  NOTE: SIZE is a constant in utility.h that represents the maximum dimension of the grid, which has the value 6. Assignment Writing Service

  	char grid[SIZE][SIZE];
  	fillGrid(grid, ALNUM);
  	printGrid(grid);

  Then the following content should print: Assignment Writing Service

  	--- --- --- --- --- ---
  	| A | B | C | D | E | F |
  	--- --- --- --- --- ---
  	| G | H | I | J | K | L |
  	--- --- --- --- --- ---
  	| M | N | O | P | Q | R |
  	--- --- --- --- --- ---
  	| S | T | U | V | W | X |
  	--- --- --- --- --- ---
  	| Y | Z | 0 | 1 | 2 | 3 |
  	--- --- --- --- --- ---
  	| 4 | 5 | 6 | 7 | 8 | 9 |
  	--- --- --- --- --- ---

  We have implemented printGrid() for you, and its RME can be found in utility.h. Feel free to use this helper function when testing other functions in polybius.h. Assignment Writing Service

mixKey()

• Notice that this function “requires” that key does not contain duplicate characters and consists of only uppercase alphabet and numbers. This means that you do not have to handle duplicate characters or lowercase alphabet. You will later handle duplicate characters and lowercase alphabet in ciphers.cpp. Assignment Writing Service

• As an example of how this function works, suppose in test.cpp you try to mix the key "POLYBIUS", call it, and print its return value like this: Assignment Writing Service

  cout << mixKey("POLYBIUS") << endl;

  Then the following content should print: Assignment Writing Service

  POLYBIUSACDEFGHJKMNQRTVWXZ0123456789

  NOTE: Make use of the constant string ALNUM defined in utility.h. You should always begin with the alphabet and digits in their original order. Assignment Writing Service

findInGrid()

• Notice that this function “requires” that c is an uppercase alphabet or a digit. This means that you do not have to handle lowercase alphabet. Assignment Writing Service

• As an example of how this function works, suppose in test.cpp you call findInGrid with 'A' as c, a grid filled as follows, and printing its return value like this: Assignment Writing Service

  	char grid[SIZE][SIZE];
  	fillGrid(grid, ALNUM);
  	cout << findInGrid('A', grid) << endl;

  Then the following content should print: Assignment Writing Service

  00

polybiusSquare()

• Notice that this function “requires” that key does not contain duplicate characters and consists of only uppercase alphabet and numbers. This means that you do not have to handle duplicate characters or lowercase alphabet. You will later handle duplicate characters and lowercase alphabet in ciphers.cpp. Assignment Writing Service

• Then the following ciphertext should print:
  Assignment Writing Service

• 11110533 000102 1533 341411 04113334

  Remember that decrypting uses the same grid as encrypting! As an example: Assignment Writing Service

  	char grid[SIZE][SIZE];
  	cout << polybiusSquare(grid, "183", "11110533 000102 1533 341411 04113334", false) << endl;

  And this is the output: Assignment Writing Service

  EECS 183 IS THE BEST

IMPORTANT: Note that spaces are allowed in the original message, and they must stay as spaces in the encrypted message as well. Assignment Writing Service

ciphers.cpp

WARNING: Sanity check! At this point, utility.cpp, caesar.cpp, vigenere.cpp, and polybius.cpp should have implementations of all functions that we declared in utility.h, caesar.h, vigenere.h, and polybius.h, and test.cpp should have a test suite for those functions. If you have not yet submitted, we highly encourage you to do so, unless you are starting late and it is close to the deadline so you have few submissions remaining. Assignment Writing Service

Overview

• Note: The autograder tests for ciphers.cpp test only your ciphers.cpp file. The autograder tests for ciphers.cpp will use EECS 183 staff implementations for the other files, like caesar.cpp. A common problem students encounter in implementing functions in ciphers.cpp is violating the Requires clause of RMEs for the functions in the other files, like caeser.cpp, vigenere.cpp, and polybius.cpp. If your solution seems to work on your computer, but fails test cases in the autograder for ciphers.cpp, check very carefully that you are not providing an argument from a function call in ciphers.cpp that would violate the Requires of the RME for that function. Assignment Writing Service

• At the top of the file, you’ll notice this line that lets ciphers.cpp use functions that are declared in utility.h, caesar.h, vigenere.h, and polybius.h: Assignment Writing Service

  	#include "utility.h"
  	#include "caesar.h"
  	#include "vigenere.h"
  	#include "polybius.h"

  after the multiline comment. Assignment Writing Service

• Implement the ciphers function in ciphers.cpp. Let us recommend this structure: Assignment Writing Service

  	void ciphers() {
  	// ask user for cipher (Caesar, Vigenere, or Polybius)
  	// ask user to encrypt or decrypt
  	// get message from user
  	// get key or keyword from user
  	// encrypt or decrypt message using selected cipher and key(word)
  	// print encrypted/decrypted message
  	}

• When you ask the user for input be sure to use these prompts, followed by a single space, in this order: Assignment Writing Service

  When encrypting, Assignment Writing Service

  	Choose a cipher (Caesar, Vigenere, or Polybius):
  	Encrypt or decrypt:
  	Enter a message:
  	What is your key:
  	The encrypted message is:

  Or when decrypting, Assignment Writing Service

  	Choose a cipher (Caesar, Vigenere, or Polybius):
  	Encrypt or decrypt:
  	Enter a message:
  	What is your key:
  	The decrypted message is:

  Expect the user to be bad at capitalization and accept input ignoring the case, such as Assignment Writing Service

  	cAEsar
  	vigenEre
  	POLYBIus
  	ENCRYPT
  	decrypt

  You must also accept c, v, p, e and d (or uppercase versions) as valid input. If an invalid cipher type or mode (encrypt or decrypt) is entered, you must print out the message Invalid cipher! or Invalid mode!. Assignment Writing Service

  We recommend using getline to read strings, so as to read more than just the first word of the keyword or message. Assignment Writing Service

  NOTE: For the caesar cipher, you can assume the user will always enter a key that is an integer when they have selected to use a Caesar cipher. Assignment Writing Service

• Then print the encrypted/decrypted message on the same line. Assignment Writing Service

• Because you’ll probably be repeating some code in ciphers.cpp, like prompting the user for a string and reading that string, it’s a good idea to factor out common functionality into separate functions. Declare those functions in ciphers.cpp (not in utility.h) above ciphers and implement them below ciphers. Be sure to write RME comments above those functions’ declarations to maximize style points. Assignment Writing Service

WARNING: Be sure not to modify any of the header files, since we’ll be using the original version when grading your project. Assignment Writing Service

• So that we can automate some tests of your code, your program must behave per the examples below. Assumed that the red underlined text is what some user has typed.

Error handling in ciphers()

WARNING: This section applies to the ciphers() function in ciphers.cpp. These are not instructions for how to implement each cipher - caesar, vigenere, or polybius. These are instructions for how to handle user input within the ciphers() function so that your ciphers.cpp does not violate the Requires clause of the RMEs for your caesarCipher, vigenereCipher, and polybiusSquare functions. Assignment Writing Service

Your ciphers() function must not violate the Requires clause of the RME for any functiuon. Since the user may enter values that may do so, you must catch these and either print an error message, or modify the input values to conform to the Requires clause before calling the corresponding cipher function. Assignment Writing Service

Here are the errors you must handle in ciphers(): Assignment Writing Service

• If the user enters an invalid cipher type (anything other than what is defined above), print Invalid cipher!, and exit the program, i.e., return; from ciphers(). Assignment Writing Service

• If the user enters an invalid mode (anything other than what is defined above), print Invalid mode!, and exit the program, i.e., return; from ciphers(). Assignment Writing Service

• For Caesar Cipher, you can assume that the user will always enter an integer-valued key when they have selected to use the Caesar Cipher. You do not need to handle the case where they enter a non-integer key. Assignment Writing Service

• For Vigenere Cipher, you must ensure that the keyword contains at least one alphabetical character. If not, print Invalid key!, and exit the program, i.e., return; from ciphers(). Assignment Writing Service

• For Polybius Square, you must ensure that the message is valid. That is, you must verify that all characters are alphanumeric or a space. Lowercase letters are valid, but the message must be converted to uppercase before calling the polybiusSquare function. Assignment Writing Service

  If an invalid message is entered, you must print Invalid message!, and exit the program, i.e., return; from ciphers(). Assignment Writing Service

• For Polybius Square, you must ensure that the key is valid. That is, you must verify that all characters are alphanumeric, all characters are uppercase, and that there are no duplicates. To ensure this, the key must be converted to uppercase, and duplicates must be removed from the key before calling the polybiusSquare function. Non-alphanumeric characters in the key should not be removed, but instead should result in an error message. Assignment Writing Service

  If an invalid key is entered - containing anything other than alphanumeric characters - you must print Invalid key!, and exit the program, i.e., return; from ciphers(). Assignment Writing Service

• HINT: think of which functions in utility.h you can use to accomplish the above requirements. Assignment Writing Service

Sample Output

When you run ciphers.cpp, it should behave per the examples below. Assume that the red underlined text is what some user has typed. Assignment Writing Service

NOTE: The following sample runs do not include the menu selection detailed in Creating a Project. Assignment Writing Service

Sample Run 1 Assignment Writing Service

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