How Does Simple Encryption Work in Java Programming?

[philippe311]

Hello,


My professor wants us to code a program that encrypts a massage and decrypt it , I know that to encrypt something you need a message and a key, and you assign a number to each letter or the message, and you do the same with the key, and then you add the two numbers together to get the message encrypted

for example if the message was
abcabc
and the key was
bcd

and

a = 0
b = 1
c = 2
d = 3

we do this to encrypt it
abcabc
bcdbcd
--------
235235

and 235235 is bdfbdf according to the assigned values of a, b, c, and d

so the final encrypted message is bdfbdf

--------------
this is what i wrote, but it only encrypts one letter of the message, and it uses one letter of the key, i need an idea of how to make it work for more than one letter

import java.util.Scanner;

public class assign3
{
public static String[] array ={"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"};

public static void main(String [] args)
{


Scanner input = new Scanner (System.in);

System.out.println("insert messege =");
String message = input.next();
int i = 0;
int num = 0;

char ch;
while(i < message.length()){
ch = message.charAt (i);
num = ch - 'a';
System.out.println(num);
i = i +1;
}



System.out.println("insert key =");
String key = input.next();
char ch2;
ch2 = key.charAt (0);
int num2 = ch2 - 'a';
System.out.println(num2);


int q;

q = num + num2;
System.out.println("encrypted number = " + q);

if (q>=26)
{
q = q%26;
}


System.out.println("Encrypted letter = " + array[q]);
}


}

 

[Mark44]

Hello,


My professor wants us to code a program that encrypts a massage and decrypt it

That would be message. Massage is something entirely different.

, I know that to encrypt something you need a message and a key, and you assign a number to each letter or the message, and you do the same with the key, and then you add the two numbers together to get the message encrypted

for example if the message was
abcabc
and the key was
bcd

and

a = 0
b = 1
c = 2
d = 3

we do this to encrypt it
abcabc
bcdbcd
--------
235235

and 235235 is bdfbdf according to the assigned values of a, b, c, and d

so the final encrypted message is bdfbdf

--------------
this is what i wrote, but it only encrypts one letter of the message, and it uses one letter of the key, i need an idea of how to make it work for more than one letter

I added [ code] tags to format your code.

import java.util.Scanner;

public class assign3
{
	public static String[] array ={"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"};

	public static void main(String [] args)
	{


		Scanner input = new Scanner (System.in);

			System.out.println("insert messege =");
			String message = input.next();

I think that you are getting only one character from the line above. Same for your code to input the key.

			int i = 0;
			int num = 0;
			
			char ch;
			while(i < message.length()){
				ch = message.charAt (i);
				num = ch - 'a';
				System.out.println(num);
				i = i +1;
			}

			

			System.out.println("insert key =");
			String key = input.next();
			char ch2;
			ch2 = key.charAt (0);
			int num2 = ch2 - 'a';
			System.out.println(num2);


			int q;

			q = num + num2;
			System.out.println("encrypted number = " + q);

			if (q>=26)
			{
				q = q%26;
			}


			System.out.println("Encrypted letter = " + array[q]);
	}


}

Is there some reason you're using the Scanner class to do I/O? You can do input as you are doing, but you need to have a loop to read all the characters of the message and the key, not just a single character each. Another possibility for input is the BufferedReader class using its readLine() method.