Question

Write a program in java that can perform encryption/decryption. In the following let the alphabet A be A={A, a, B, b, . . ., “ ”, “.”,“’ ”}. The encoding is A→0, a→1, B→2, b→4, . . ., Z→50, z→51, “ ”→52, “.”→53 and “’”→54.

Answer 1

package Security;

import java.util.Scanner;

// Defines a class for encryption and decryption

public class EncDec

{

// Creates a character array

char letters[] = {'A', 'a', 'B', 'b', 'C', 'c', 'D', 'd',

'E', 'e', 'F', 'f', 'G', 'g', 'H', 'h', 'I', 'i',

'J', 'j', 'K', 'k', 'L', 'l', 'M', 'm', 'N', 'n',

'O', 'o', 'P', 'p', 'Q', 'q', 'R', 'r', 'S', 's',

'T', 't', 'U', 'u', 'V', 'v', 'W', 'w', 'X', 'x',

'Y', 'y', 'Z', 'z',' ', '.', '\''};

// Method to encrypt data and returns it

String encryption(String ori)

{

// To store encrypted data

String encrypted = "";

// Loops till end of the string

for(int c = 0; c < ori.length(); c++)

{

// Flag value 0 for not available character

// for encoding

int f = 0;

// Extracts a character

char ch = ori.charAt(c);

// Loops till end of the letters array

for(int d = 0; d < letters.length; d++)

{

// Checks if current extracted character

// is same as letters array d index position

// character

if(ch == letters[d])

{

// Adds the index position to encrypt

encrypted += d;

// Adds -1 as split character

encrypted += -1;

// Sets the flag to 1 for available

f = 1;

// Come out of the loop

break;

}// End of if condition

}// End of for loop

// Checks if flag is 0 then add the original

// character

if(f == 0)

encrypted += ch;

}// End of outer for loop

// Returns the encrypted data

return encrypted;

}// End of method

// Method to decrypt data and returns it

String decryption(String enc)

{

String decrypted = "";

// Split data with -1

String splitString[] = enc.split("\\-1");

// To store the array position

int pos = 0;

// Loops till end of the split array

for(int c = 0; c < splitString.length; c++)

{

// Extract a character

char ch = splitString[c].charAt(0);

// Check if the character is a digit

if(Character.isDigit(ch))

{

// Convert the split data to integer

pos = Integer.parseInt(splitString[c]);

// Add the letter at pos index position

decrypted += letters[pos];

}// End of if condition

// Otherwise add the split data

else

decrypted += splitString[c];

}// End of for loop

// Returns the decrypt data

return decrypted;

}// End of method

// main method definition

public static void main(String ss[])

{

// Scanner class object created

Scanner sc = new Scanner(System.in);

// Class EncDec object created

EncDec ed = new EncDec();

// Accepts the string to encrypt

System.out.print("\n Enter a string to encrypt: ");

String original = sc.nextLine();

// Calls the method to encrypt and stores the result

String encryptedString = ed.encryption(original);

// Displays the original data

System.out.print("\n Original string: " + original);

// Displays the encrypted data

System.out.print("\n Encrypted string: " + encryptedString);

// Accepts the string to decrypt

System.out.print("\n Enter a string to decrypt: ");

encryptedString = sc.nextLine();

// Calls the method to decrypt and stores the result

String decryptedString = ed.decryption(encryptedString);

// Displays the decrypted data

System.out.print("\n Decrypted string: " + decryptedString);

}// End of main method

}// End of class

Sample Output:

Enter a string to encrypt: This is demo.

Original string: This is demo.
Encrypted string: 38-115-117-137-152-117-137-152-17-19-125-129-153-1
Enter a string to decrypt: 38-115-117-137-152-117-137-152-17-19-125-129-153-1

Decrypted string: This is demo.