COMP 1010代做、代写Java，Python程序语言、代做c++编程代写

日期：2020-11-05 11:30

ASSIGNMENT 3: Strings, chars, and Loops (Units 1-13)

DEPARTMENT ANDCOURSE NUMBER: COMP 1010

COURSE TITLE: Introduction to Computer Science1

TERM:Fall2020

Assignment3

DUEDATE: NOVEMBER 6, 2020 BY 11:59 PM CDT

SubmissionGuidelines:

• Name your sketch using your name, and the assignment number, exactly as in this example:

LastnameFirstnameA3Q3. You will submit only one program in this assignment, for

the highest question completed.

• There are marks for the behaviour of your program, and marks for coding. If your program

does not run upon download, you will not receive any marks for program behaviour.

• Assignments must follow the programming standards document published on the course

website on UM Learn.

• After the due date and time assignments may be submitted but will lose 2% of marks per

hour late or portion thereof. The date and time of the last file submitted controls the mark for

the entire assignment.

• You may submit your program multiple times, but only the most recent version will be

marked.

• These assignments are your chance to learn the material for the exams. Code your

assignments independently. We use software to compare all submitted assignments to each

other, and pursue academic dishonestly vigorously.

Note:

This assignment is an opportunity to demonstrate your knowledge of Strings, chars, and loops.

Even if you know arrays, or other data structures, they should not be used on this assignment.

This assignment makes use of global variables, because we haven’t yet covered how to pass data

to and from user-defined functions (that’s Unit 14). If you have read ahead, you’re welcome to

modify the user-defined functions to use parameters and return values instead of relying on

global variables. However, this is not required.

Each question builds on the previous question. Make sure that you follow ALL instructions

carefully and finish one question completely before moving on to the next question. You are

asked to do certain things in a specific way so that you don’t run into difficulty later.

Background:

Cryptography is the study and practice of creating secure, private communication that can not

be understood by anyone that intercepts the information. Modern cryptography underlies much

of the modern world including e-commerce, computer passwords, and more.

Modern cryptography algorithms are quite sophisticated but, prior to electronic computers,

cryptography focused on encryption: the process of taking readable information and making it

look unreadable, often using a secret key. The un-encrypted text is called the plaintext, and the

encrypted text is called the ciphertext. The process of turning the ciphertext back into plaintext

is called decryption.

ASSIGNMENT3

DEPARTMENTANDCOURSENUMBER:COMP1010

2

CaesarShiftAlgorithm

You should be able to do Q1 & Q2 after Week 7. They cover String, chars, and loops.

Write an Active Processing program to implement the Caesar Cipher (also known as the

Caesar Shift or shift cipher).

The Caesar Cipher is one of the simplest ways to encrypt a message (it’s also one of the easiest

to decrypt, so it’s not very secure). It is a type of substitution cipher, meaning that each letter in

the plaintext is replaced one at a time in order to produce the ciphertext.

In the Caesar Cipher, each letter of the plaintext is replaced by the letter that is KEY positions

later in the alphabet. For example, if KEY =3, then the letter ‘a’ will be replaced by ‘d’, ‘b’ will

be replaced by ‘e’, and so on, up until ‘z’ which will be replaced by ‘c’.

Note: the Caesar Shift that we are implementing will only encrypt/decrypt letters (not

numbers, punctuation, spaces, etc.).

So for KEY = 3 each plaintext letter of the alphabet will be encrypted into the following

ciphertext letter:

0 1 2 3 4 5 6 7 8 9 10 11 12

plaintext a b c d e f g h i j k l m

cipher d e f g h i j k l m n o p

13 14 15 16 17 18 19 20 21 22 23 24 25

plaintext n o p q r s t u v w x y z

cipher q r s t u v w x y z a b c

We can encrypt messages using the Caesar Cipher by first assigning each letter of the alphabet to

a number from 0 to 25. Then, for each character in the plaintext, find the corresponding number

value, and add KEY modulo 26. To decrypt the message, this process is reversed.

Here is an example of the plaintext “theansweris” encrypted using the KEY = 3:

plaintext t h e a n s w e r i s

plaintext as number 19 7 4 0 13 18 22 4 17 8 18

( plaintext + KEY ) mod 26 22 10 7 3 16 21 25 7 20 11 21

ciphertext w k h d q v z h u l v

Mathematically, the Caesar shift encryption of a letter x by a KEY can be written as:

EKEY(x) = ( x + KEY ) mod 26

and the decryption can be represented mathematically as:

DKEY(x) = ( x – KEY ) mod 26

Recall that char values are stored as a numbers by the computer, but it’s not as simple as a = 0,

b =1, etc. We are using the ASCII encoding, and so you will need to take that into account in

your encryption (and decryption) equations.

ASSIGNMENT3

DEPARTMENTANDCOURSENUMBER:COMP1010

3

Q1:CaesarShift[8 marks]

• Create a global integer constant KEY=3.

• In the setup() function, call the noLoop() command so that draw() will only run once.

All repetition in this assignment will be done with loops later on.

• Note that none of the code you will write in this assignment will use the Processing canvas,

so you do not need to include a size() command in setup().

• Ask the user for some plaintext to encrypt:

o At the very beginning of your program, import JOptionPane using the statement

importjavax.swing.JOptionPane;

o Create three global String variables called userInput, encryptedText, and

decryptedText. Initialize each of them to be an empty String.

o In your draw() function, use JOptionPane.showInputDialog() to get a

plaintext String from the user, and store this value in userInput. Make sure to give

your dialogue box a reasonable prompt.

o The user should only enter text that consists entirely of letters (a-z and A-Z), no

numbers, punctuation, or spaces. In the program, we can assume that any text entered

by the user is valid for now. We’ll verify the user input in Q5.

o Note: if you click “Cancel” on the input dialog box the program will “crash”. That’s

ok, we haven’t learned how to handle that. Just stop your program manually.

• Write a function called caesarEncrypt()

o This function will encrypt the userInput using the Caesar Cipher described above.

o The amount of the shift is KEY.

o Do not change or modify userInput in any way. Instead, store the ciphertext in the

encryptedText variable.

o The encryptedText should be in all lowercase letters. (Hint: it is easiest to make a

version of the plaintext in all lower case letters first, and then encrypt it. This way you

don’t need to deal with both upper and lower case letters).

o At the end of the function, print a message with the userInput and encryptedText

to the console in the following format:

You entered the plaintext: ComputerScience

and the ciphertext is: frpsxwhuvflhqfh

• Write a function called caesarDecrypt()

o This function will decrypt the userInput using the Caesar Cipher described above.

o The amount of the shift is KEY (notice that this time we subtract KEY from each letter).

o Do not change or modify userInput in any way. Instead, store the decrypted

plaintext in the decryptedText variable.

o The decryptedText should be in all lower case letters.

o At the end of the function, print a message with the userInput and decryptedText

to the console in the following format:

You entered the ciphertext: frpsxwhuvflhqfh

and the plaintext is: computerscience

ASSIGNMENT3

DEPARTMENTANDCOURSENUMBER:COMP1010

4

• In draw(), call caesarEncrypt()after asking the user for the plaintext. Then, ask the

user for input again and call caesarDecrypt(). Note that at this point your draw()

function should only have four lines of code.

Q2:ChangingtheKEY[3 marks]

Now let’s make things more interesting, by allowing the user to pick the encryption key.

• Modify the global constant KEY to be an integer variable called shiftKey. Give shiftKey

an initial value of zero.

o Make sure to replace KEY everywhere in your program with shiftKey.

• In draw(), before any of the other code, use JOptionPane.showInputDialog() to ask

the user to enter an integer value for the key. JOptionPane will return a String value, so

you’ll need to turn it to an integer before storing the value in shiftKey. (Hint: Processing

has an int() function).

• But what if the user doesn’t enter a valid number? After converting the user input into an

integer, check if the value of shiftKey is between 1 and 25 inclusive. If it’s not, keep

asking the user for a new number until a valid number is entered.

o Note: When the int() function is used on a String, it will return the value 0 for any

String containing characters other than digits (such as letters or symbols).

Q3:StopthePop-UpBoxes [2 marks]

You should be able to do the remaining questions after Week 8 in the course.

Modify your draw() function so that all of the code currently in draw() runs over and over again

until the text that the user wants to decrypt is “quit”.

When the value of userInput to decrypt is “quit”, the program should decrypt this word and

then stop prompting the user for any additional input. Use the command exit() to end the

program and close the canvas.

VigenèreCipher Algorithm

The Vigenère Cipher is another substitution cipher that is more sophisticated than the Caesar

Shift. Rather than having a single numeric KEY, the Vigenère Cipher uses a keyword.

This keyword is repeated until it matches the length of the plaintext.

Each letter in the plaintext and keyword is converted to the corresponding number between 0 and

25 (A = 0, B = 1, … Z = 25, just like in the Caesar Shift). The numeric value of each letter of the

plaintext is added to the numeric value of the corresponding letter in the keyword, modulo 26.

Mathematically, we can represent the encryption of each plaintext letter Pi into a ciphertext letter

Ci using the keyword letter Ki in the Vigenère Cipher as:

Ci = ( Pi + Ki ) mod 26

To decrypt a ciphertext letter Ci into plaintext letter Pi with keyword letter Ki:

Pi = ( Ci – Ki + 26 ) mod 26

ASSIGNMENT3

DEPARTMENTANDCOURSENUMBER:COMP1010

5

For example, if the keyword is COMPUTER, with the plaintext “THEANSWERIS”

Plaintext THEANSWERIS Plaintext as number 197401318 22417818

Key COMPUTERCOM Key as number 2141215201941721412

Ciphertext VVQPHLAVTWE (Plaintext + Key ) % 26 2121161571102119224

Q4:VigenèreCipher[6 marks]

• Create a global String constant called KEYWORD . The value of KEYWORD should be your first

name without any punctuation in all upper case letters.

• Write a function called vigenereEncrypt()

o This function will encrypt the userInput using the Vigenère Cipher described above.

o Do not change or modify userInput in any way. Instead, store the ciphertext in the

encryptedText variable.

o The encryptedText should be in all UPPERCASE letters.

o At the end of the function, print a message with userInput and encryptedText to

the console in the same format as Q1.

• Write a function called vigenereDecrypt()

o This function decrypt the userInput using the Vigenère Cipher described above.

o Do not change or modify userInput in any way. Instead, store the decrypted

plaintext in the decryptedText variable.

o The decryptedText should be in all UPPERCASE letters.

o At the end of the function, print a message with the userInput and decryptedText

to the console in the same format as Q1.

• Make sure to test these functions! One way to do that is to comment out the code in draw()

that calls the Caesar Shift encryption/decryption functions, and call the these ones instead. In

particular, make sure to test these functions with text that is longer than your name.

Q5: Validateuserinput[3 marks]

Both of our Caesar Cipher and Vigenère Cipher can only encrypt and decrypt letters of the

alphabet. In this question create a function to check that the plaintext or ciphertext entered by the

user only contains letters.

• Create a global boolean variable called isAllLetters.

• Create a function called checkAllLetters()

o In the checkAllLetters() function, check each character of userInput. If every

character is a letter set the value of isAllLetters to true. If one or more characters

in userInput is not a letter, set the value of isAllLetters to false.

o Hint: the function Character.isLetter() checks if a char is a letter

ASSIGNMENT3

DEPARTMENTANDCOURSENUMBER:COMP1010

6

Q6: Putitalltogether [6 marks]

Modify your draw() function so that your program has the following behaviour:

• Using JOptionPane.showInputDialog(), ask the user to type in one of three options:

“Caesar”, “Vigenere”, or “Quit”.

o Give the dialog box an appropriate prompt that tells the user what to type in for each

of the three selections.

o Capitalization does not matter for any of the options. The program should recognize

“Caesar”, “caesar", “CAESAR” , “CaEsAr”, etc. as the same.

o Save the user’s selection in userInput.

• If the user enters “Caesar”, the program should prompt the user for a key until a valid value

is entered (this is your code from Q2)

o Once a valid key has been entered, prompt the user for text to encrypt. Use your

checkAllLetters() function to check the input, and keep prompting the user for a

value until they have entered plaintext that is valid (i.e. all letters). Encrypt this text

using your caesarEncrypt() function.

o Next, prompt the user for text to decrypt. Again, use your checkAllLetters()

function to check the input and keep prompting the user until they enter valid text.

Decrypt this text using your caesarDecrypt() function.

• Otherwise, if the user enters “Vigenere”:

o Prompt the user for text to encrypt. Make sure that the text is valid, and keep

prompting the user until they enter text that only contains letters. Encrypt this plaintext

using your vigenereEncrypt() function.

o Prompt the user for text to decrypt, make sure that it is valid, and keep prompting the

user until valid text is entered. Decrypt this text using vigenereDecrypt().

• Otherwise, if the user enters “Quit”:

o Stop prompting the user for any input.

o Note: “Quit” should only work from this menu. If the user enters “Quit” when

prompted for plaintext or ciphertext, the program should not end.

• After completing the Caesar Shift or Vigenère Cipher selection, the program should

prompt the user to type in an option again from “Caesar”, “Vigenere”, or “Quit”.

• If anything else is entered other than the three possible options, the program should

ignore it and prompt the user to type in an option again.

[ProgrammingStandardsareworth5marks]

Hint:SomeusefulStringandcharfunctions that you mayormaynotwanttouse.Notallofthem

are usefulforthisassignment.

Formoreinformationabouteachfunction,checkouttheProcessingReferenceLibrary.

• equals()

• equalsIgnoreCase()

• charAt()

• toLowerCase()

• toUpperCase()

• substring()

• isLowerCase()

• isUpperCase()

• isLetter()

• isDigit()