Encrypt and decrypt a string

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I want to encrypt and decrypt a string which contains alphabets from A-Z using java
Encryption:-For example i have a string from A-Z and user gives A as input then the output must be 1 in this way if user inputs B then output must be 2 and soon up to Z.

Decryption:-For example i have a string from A-Z and user gives 1 as input then the output must be A in this way if user input 2 then output must be B and soon up to Z.

i was able to solve decryption but i am not able to solve encryption.please remember while answering that Iam a beginner and i want to write the encryption program and decryption program in one program only.

What I have tried:

Java

import java.util.Scanner;
import java.lang.String;
public class Decrypt {

		public static void main(String[] args){
			
			Scanner sc=new Scanner(System.in);
		    String s1 = " ABCDEFGHIJKLMNOPQRSTUVWXYZ";
		   int n = sc.nextInt();
		    char ch = s1.charAt(n);
		    
		    System.out.println(ch);
		   
	            }  
	         
	        }

Posted 6-Nov-18 17:36pm

Member 14046337

Updated 7-Nov-18 5:40am

Patrice T

v3

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Comments

CPallini 7-Nov-18 5:32am

I see a problem in your encryption/decryption logic. For instance, on encryption K->11.
Then, on decryption, 11->K or 11->AA ?

MadMyche 7-Nov-18 8:11am

Nice

Member 14046337 7-Nov-18 9:24am

i want decryption 11- k and encryption k-11.

CPallini 7-Nov-18 11:23am

The you have to put separators (e.g. blanks) in the encrypted string, otherwise decryption won't be feasible, due to such ambiguties. Or possibly your encrypted info is an array of integers?

MadMyche 7-Nov-18 8:13am

(hint) So basically you just want to get the ASCII value and substract 64 to "encrypt" (sic)

3 solutions

Solution 1

If you can't solve encryption, then you can't solve decryption, because you don't have "genuine" encrypted examples to test against. And since decryption is the exact reverse of encryption solving one pretty much gives you the code for the other!

This is a minor variation of the Caesar Cypher: and you will find many, many examples of that implemented in pretty much every language: Caesar Cypher java - Google Search[^] offers 68,000 hits.

But do bear in mind that a Caesar Cypher isn't "real encryption", and isn't at all secure - they publish whole magazines full of them (generally called "Codebreaker" or similar) every month so really bored people can solve them in their spare time instead of watching Jeremy Kyle or yet another putrid game show...

Posted 6-Nov-18 20:49pm

OriginalGriff

Solution 3

Thank u for everyone help.This is even better than stack overflow

import java.util.Scanner;
public class Encrypt {

		public static void main(String[] args){
			Scanner sc=new Scanner(System.in);
		    String s1 = " ABCDEFGHIJKLMNOPQRST";
		     int n = sc.nextInt();
		    char ch = s1.charAt(n);
		    
		    System.out.println(ch);
		
		    
	String ss = sc.next();    // get the next token

ss = ss.toUpperCase();     // convert to upper case
for (int i = 0; i < ss.length(); ++i)  // for each character in the token
{
    char c = ss.charAt(i);
    System.out.print("Letter is: " + c);          // display the character
    int val = c - 'A' + 1;                        // get its numeric value
    System.out.println(" , Value is: " + val);    // display the value
}}}

Posted 7-Nov-18 5:40am

Member 14046337

Comments

Evrim Tekin 7-Nov-18 20:08pm

Hi

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Richard MacCutchan · Accepted Answer · 2018-11-06T21:47:00

Solution 2

Java

String ss = sc.next();    // get the next token
ss = s.toUpperCase();     // convert to upper case
for (int i = 0; i < ss.length(); ++i)  // for each character in the token
{
    char c = ss.charAt(i);
    System.out.print("Letter is: " + c);          // display the character
    int val = c - 'A' + 1;                        // get its numeric value
    System.out.println(" , Value is: " + val);    // display the value
}

Note, this needs the addition of error checks to ensure that each character is alphabetic only.

Posted 6-Nov-18 21:47pm

Richard MacCutchan

Comments

CPallini 7-Nov-18 5:12am

Such an encryption would be undecryptable, unless you put separators between the generated integers.

Richard MacCutchan 7-Nov-18 5:16am

I know, but it answers the question.

CPallini 7-Nov-18 5:22am

I see. Now I wonder how the OP was 'able to solve decryption'.

Richard MacCutchan 7-Nov-18 5:52am

It's not decryption (or encryption) it's substitution.

Member 14046337 7-Nov-18 9:52am

ss=s.toUppercase();.Here s is showing some errors.

Richard MacCutchan 7-Nov-18 10:35am

Typo, obviously should be ss=ss.toUppercase();

Richard MacCutchan 7-Nov-18 10:38am

And a reminder ...
When you get errors in your code and want to report them to us, do not just say "some errors". Show us the exact message that you see. Even though in this case the problem was obvious.

Member 14046337 7-Nov-18 11:30am

Sir one last doubt why we write int val = c - 'A' + 1; and at last code project community is better than stacks overflow.

Richard MacCutchan 7-Nov-18 12:48pm

A character is just a byte with a numeric value, each alphabetic character is 1 greater than the previous. The character A has the value x41, or 65 decimal, B is 66 etc. So if you subtract 'A' (65) from whichever character is entered, you get its index value in the alphabet. But in this case 'A' would be zero, so we add one to make it a 1 based list.