Java Ascii to String Decryption

Question

I'm completing a problem for class that requires converting a string message from ascii with a key to a decoded String message. I've tried both accessing the string from message.charAt(i) and by converting it to a char array but both times I get this weird out put on the console.

This is the method I have running

public static char[] decrypt(String message) {
    char[] decoded = new char[message.length()];
    char[] newmessage = message.toCharArray();
    int ascii;
    for(int key=0; key<=100; key++) {
        for(int i=0; i<message.length(); i++) {
            ascii = ( (int)newmessage[i] + 127) - 32;
            if(ascii > 126)
                decoded[i] = (char)((int)newmessage[i] - key);
            else
                decoded[i] = (char)((((int)newmessage[i] - key) +127) -32);
        }
    }
    System.out.println(decoded);
    return decoded;
}

This is where I called it in main

    System.out.println("Problem 3");
    String message =  ":mmZ\\dxZmx]Zpgy";
    System.out.println("Message Received: ");
    System.out.println(message);
    decrypt(message);

I can't seem to figure out where I went wrong with it. The expected output is for each key to be printed with the corresponded decoded message. The 88th key will show the message is "Attack at Dawn!".

Why you are looping through 100 times? What is your actual and expected output. — Ashraff Ali Wahab
– Ashraff Ali Wahab, Commented Sep 17, 2018 at 16:01
part of the question was that the key for the code was between 1 and 100 and we had to show the gibberish produced by every other key. I will post a link to the original question. — lio
– lio, Commented Sep 17, 2018 at 16:04
The message is actually in unicode as Java use it by default — Maxim
– Maxim, Commented Sep 17, 2018 at 16:04
is this in regards to the title? or is this something that has to be addressed in the code? — lio
– lio, Commented Sep 17, 2018 at 16:08

bobah · Accepted Answer · 2018-09-17 16:13:51Z

2

If all you need is decode from ASCII to Java String, then one of correct ways of doing it is

char [] output = StandardCharsets.US_ASCII.decode(ByteBuffer.wrap(input)).array();

Based on your performance requirements, you may want to preallocate buffers, and may be the decoder (in the above example Charset::decode will create one on the fly).

answered Sep 17, 2018 at 16:13

bobah

19k2 gold badges43 silver badges74 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Gatusko · Accepted Answer · 2018-09-17 16:26:09Z

Okey first you need to now wich Key decode the message of :mmZ\\dxZmx]Zpgy So for go for the easy part try to decode first the Hey message with your algorithm that you made, and you forgot the most escenssial part:

if(originalChar + key > 126) then
     EncryptedChar = 32 + ((originalChar + key) - 127)
else
     EncryptedChar = (originalChar + key)

So you in your if statement you are missing the minus key

 if(ascii - key > 126)

Always go and re read your question.

    for(int key=0; key<=100; key++) {
        for(int i=0; i<message.length(); i++) {
            ascii = ( (int)newmessage[i] + 127) - 32;
            if(ascii - key > 126)
                decoded[i] = (char)((int)newmessage[i] - key);
            else
                decoded[i] = (char)((((int)newmessage[i] - key) +127) -32);
        }
        System.out.println("Decoded with i=" +key +":"+new String(decoded)); // For check what is the correct message. 
    }

Spoiler The MEssage is: Attacck at dawn!

Collectives™ on Stack Overflow

Java Ascii to String Decryption

2 Answers 2

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related