Java DES Wrong Encryption

Question

I have coded DES in Java using builtin Libraries but I am not getting the right Encryption Result. Please explain me where I am making a mistake

import javax.crypto.Cipher;
import javax.crypto.SecretKey;
import javax.crypto.SecretKeyFactory;
import javax.crypto.spec.DESKeySpec;
import javax.xml.bind.DatatypeConverter;

public class MainClass {

    public static void main(String[] args) {

        String l = "0e329232ea6d0d73";

        byte[] a = DatatypeConverter.parseHexBinary(l);

        try{
            DESKeySpec dks = new DESKeySpec(a);
            SecretKeyFactory skf = SecretKeyFactory.getInstance("DES");
            SecretKey sk = skf.generateSecret(dks);
        Cipher c = Cipher.getInstance("DES");
        c.init(Cipher.ENCRYPT_MODE, sk);
        String M = "8787878787878787";
        byte[] b = c.doFinal(M.getBytes());

        System.out.println(new String(b));
        c.init(Cipher.DECRYPT_MODE, sk);
        System.out.println(new String(c.doFinal(b)));
        }
        catch(Exception e)

        {
            System.out.println(e.getMessage());
        }   
    }

}

HexaDecimal 16 Digit Key: 0e329232ea6d0d73
Plain Text: 8787878787878787
Encryption : –m^MúÊ'+–m^MúÊ'+©ôËÓ—

Desired Encryption: 0000000000000000

This is what I am saying the answer in the encrypted output in online calculator is 0000, and mine is completely different:

What do you mean by desired result? Is it desired encrypted message or desired decrypted message? — mazhar islam
– mazhar islam, Commented Oct 15, 2016 at 23:24
The desired result of decryption is 87878787..., not 00000000... and you don't state any basis for your apparent expectation that the result of encryption will be all zeros either, which is most improbable. Unclear what you're asking. — user207421
– user207421, Commented Oct 15, 2016 at 23:27
1. Don't use DES, it is no longer considered secure, it has been superseded byAES. 2. The result of encryption is an array of bytes, not characters, if you need to display encrypted data use hexadecimal. 3. How do you expect 0000000000000000 as the encrypted result. 4. Do not use ECB mode, it is insecure, see ECB mode, scroll down to the Penguin. — zaph
– zaph, Commented Oct 15, 2016 at 23:33
For the third time, why do you think the result should be all zeros? I repeat that this is most improbable. And are these binary zeroes or ASCII zeros? — user207421
– user207421, Commented Oct 15, 2016 at 23:37

mazhar islam · Accepted Answer · 2016-10-16 10:03:32Z

1

Change

byte[] b = c.doFinal(M.getBytes());

to

byte[] b = c.doFinal(DatatypeConverter.parseHexBinary(M));

Besides, use mode ECB in your code (because you marked ECB in your picture). Like:

Cipher c = Cipher.getInstance("DES/ECB/NoPadding");

The String.getBytes() encodes the String into a sequence of bytes using the platform's default charset, storing the result into a new byte array. In your case which is an array of length 16 containing values 56 55 56 55... ASCII representation of 8787...

What you need is converting the Hex 8787... to binary.

edited Oct 16, 2016 at 10:03

answered Oct 15, 2016 at 23:57

mazhar islam

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3 Comments

Syed Khizer Abass Over a year ago

Thanks man for saving my life .. it worked for me . ok i have another question. how would i convert normal string to hexa

mazhar islam Over a year ago

You mean Converting A String To Hexadecimal In Java?

Tom Blodget Over a year ago

@user2747596 And "platform's default charset" is probably not what you want, especially since it can change and if you don't know what it is you can't communicate that the person who has to decrypt your text.

zaph · Accepted Answer · 2016-10-15 23:50:15Z

1

The data is: hex 8787878787878787 and needs to be converted to binary. `

edited Oct 15, 2016 at 23:50

answered Oct 15, 2016 at 23:47

zaph

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3 Comments

zaph Over a year ago

Convert the hax characters strig to byte[] data.

Syed Khizer Abass Over a year ago

did you mean Converting M to hexa binary ?

Syed Khizer Abass Over a year ago

can you please explain what you are trying to say ?Because i am not getting you on this

user207421 · Accepted Answer · 2016-10-16 06:20:02Z

0

The input to that online calculator is stated to be hex, which implies a data convertion. You aren't doing any hex conversion in your code: you're just providing base-10 digits in ASCII.

edited Oct 16, 2016 at 6:20

answered Oct 15, 2016 at 23:48

user207421

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4 Comments

zaph Over a year ago

Actually hex-ASCII not base-10 digits and binary is needed.

user207421 Over a year ago

@zaph It's only 'hex-ASCII', whatever that may be, if the recipient so treats it, which it doesn't. Binary is needed as an input to the encryption, but hex is a representation of binary. Base-10 digits in ASCII are also a representation of binary, but of the wrong binary value in this case.

zaph Over a year ago

It turns out that both the data and key are in hex-ascii.

Syed Khizer Abass Over a year ago

The above answer just solved my issue you were right it was the issue of M.getbytes[] it wasn't in hexa. Thanks for the answers

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