Thread: Setting up a loop for a SHA-256 hash for multiple outputs

I started only a few days ago trying to figure this out under "questions". Go there for an explanation of what I am trying to do.

I've been reading a lot and I learned a little bit more about what command and line does what and why... I am still trying to get a preferred output, but not getting it. Here's what I have so far trying to test to see if I can generate the first 17 hashes from consecutive 16 digit hexidecimal number from 0x0 to 0x10 and I am wondering why it isn't working... explanations with // below of what I try to do with each line:

import java.security.MessageDigest;
 
public class SHAHashingExample
{
    public static void main(String[] args)
    {
    	String a = "0000000000000000";
 
        // here is where I am converting a string to an integer so I can make it a loop
        for (int b = Integer.parseInt(a); b <= 17; b++); {
	for (int c=0; c <= b; c++); {
 
		// here is where I am wanting it to print the first original hex value 
		System.out.println("Original : " + c);
		}
 
                //below is the set up for the hash
        	MessageDigest md = MessageDigest.getInstance("SHA-256");
        	md.update(a.getBytes());
 
        	byte byteData[] = md.digest();
 
        	//convert the byte to hex format
        	StringBuffer hexString = new StringBuffer();
    		for (int i=0;i<byteData.length;i++) {
    			String hex=Integer.toHexString(0xff & byteData[i]);
   	     		if(hex.length()==1) hexString.append('0');
   	     		hexString.append(hex);
    		}
                //here is where it outputs the hash of the original
        	System.out.println("Hash : " + hexString.toString());
        }
        //Here is a line separator for it to print a blank line between the first Hash and the next Original
	System.out.printlm("")
    }
}

But I still get:
Original: 0000000000000000
Hash: fcdb4b423f4e5283afa249d762ef6aef150e91fccd810d43e5 e719d14512dec7
<blank line>

When I want:
Original: 0000000000000000
Hash: fcdb4b423f4e5283afa249d762ef6aef150e91fccd810d43e5 e719d14512dec7
<blank line>
Original: 0000000000000001
Hash: 665e994827f6b03167e80c1513eb356e0d4f013f2e03a3b345 e1e5e3c24dfca6
-----and so on until...-----
Original: 0000000000000010
Hash: fb4714aaedd1c0f5682d402c31131f1f85a57236e4f47cd111 acf596e3241ab4

It's not looping correctly to give me the output I want and I am not sure where I am going wrong. Is what I want to do impossible with java language or do I just not know enough yet? Or what specifically am I missing or have out of place to make it generate the multiple outputs I want? Any help would be appreciated.

Originally Posted by Norm

Can you post the code you are compiling and executing? The posted code does not compile without errors.

Here is the original one I was working with

import java.security.MessageDigest;
 
public class SHAHashingExample 
{
    public static void main(String[] args)throws Exception
    {
    	String a = "0000000000000000";
 
        MessageDigest md = MessageDigest.getInstance("SHA-256");
        md.update(a.getBytes());
 
        byte byteData[] = md.digest();
 
        //convert the byte to hex 
        StringBuffer hexString = new StringBuffer();
    	for (int i=0;i<byteData.length;i++) {
    		String hex=Integer.toHexString(0xff & byteData[i]);
   	     	if(hex.length()==1) hexString.append('0');
   	     	hexString.append(hex);
    	}
        System.out.println("Original : " + a);    	
        System.out.println("Hash : " + hexString.toString());
    }
}

Originally Posted by Norm

What was the problem with that one?

Nothing. That one is written to only give 1 output result. Per my original post, I want the consecutive output of 17 (0x0000000000000000 through 0x0000000000000010).

Originally Posted by Junky

Have you spotted the mistake yet?

In looking it over, I either need to not close off my brackets or maybe even put in a catch-return statement? Maybe it's in my print statements where I need to make a different variable so it prints something different since all it prints is just the initial value and my loops is essentially sitting there doing nothing and is overlooked with all values for a, b, and c are all equal. Or is it even as dumb as me puting semicolons after my for statements when they aren't supposed to be there?

Originally Posted by Norm

Fix the compiler errors before posting the new version of the code.

If you need help with the errors, copy the full text of the error messages and post it.

Ok, so this:

import java.security.MessageDigest;
 
public class SHAHashingExample
{
    public static void main(String[] args)throws Exception
    {
    	String a = "0000000000000000";
 
        for (int b=Integer.parseInt(a);b<=17;b++) {
 
		System.out.println("Original : " + b);
		}
        	MessageDigest md = MessageDigest.getInstance("SHA-256");
        	md.update(a.getBytes());
 
        	byte byteData[] = md.digest();
 
        	//convert the byte to hex format method 2
        	StringBuffer hexString = new StringBuffer();
    		for (int i=0;i<byteData.length;i++) {
    			String hex=Integer.toHexString(0xff & byteData[i]);
   	     		if(hex.length()==1) hexString.append('0');
   	     		hexString.append(hex);
    		}
        	System.out.println("Hash : " + hexString.toString());
 
    }
}

Gets me output of:

Original: 1
Original: 2
through
Original:17
Hash: <hex code>

Is it preferred I have the println just print as a hex value or better to have the loop define the hex value (example, System.out.println(String.format("%08X")? Also, the loop works with the original, but not the hash... hmm... I have an idea, but any hints would help... I'll keep noodling on it.

Originally Posted by Norm

What do you want to see printed?

Per first post:
Original: 0000000000000000
Hash: fcdb4b423f4e5283afa249d762ef6aef150e91fccd810d43e5 e719d14512dec7
<blank line>
Original: 0000000000000001
Hash: 665e994827f6b03167e80c1513eb356e0d4f013f2e03a3b345 e1e5e3c24dfca6
-----and so on until...-----
Original: 0000000000000010
Hash: fb4714aaedd1c0f5682d402c31131f1f85a57236e4f47cd111 acf596e3241ab4

I'm working on fixing the Original now so it prints how I want, then will try to loop the hash value. You guys really are helping and I am grateful.

Originally Posted by Norm

Work on how to create the number shown above. Give an int with value 1, how to get that String?

ok so far I got the hex values without the leading zeros by doing this:

        for (int b=Integer.parseInt(a);b<=17;b++) {
		String strHexNumber = Integer.toHexString(b);
		System.out.println("Original : " + strHexNumber);
		}

Another person I got some help from said I can convert an int to a zero-padded String with String.format(). For example:
System.out.println(String.format("%08X", 201));
But I just get errors if I try to do that with the hexString. Still trying a few things here and there, but I'm not giving up anytime soon!

Originally Posted by Norm

Since you are working with Strings, create the right most part of the String that contains the hex digits, concatenate that at the end of a long enough String of "0000"s, then use substring() to take off from the right most end of the long concatenated String the number of characters you want.

Working with an if/else string for that.

Edit:

nevermind, I see what you mean.
Using this but may need to rework it:

String prependZeros(int number) { // number >= 0
String s= "000000000000000000"+number; // 16 zeros prepended
return s.substring(s.length()-16); // keep the rightmost 16 chars

--- Update ---

Update:

Ok, here's the updated code so far, but getting an error when compiling:

import java.security.MessageDigest;
 
public class SHAHashingExample
{
    public static void main(String[] args)throws Exception
    {
    	String a = "0000000000000000";
 
        for (int b=Integer.parseInt(a);b<=17;b++) {
		String strHexNumber = Integer.toHexString(b);
			String prependZeros(b); { // number >= 0
       			String s= "00000000000000000"+b; // 15 zeros prepended
       			return s.substring(s.length()-16); // keep the rightmost 16 chars
   			}
		System.out.println("Original : " + strHexNumber);
		}
 
        	MessageDigest md = MessageDigest.getInstance("SHA-256");
        	md.update(a.getBytes());
 
        	byte byteData[] = md.digest();
 
        	//convert the byte to hex format
        	StringBuffer hexString = new StringBuffer();
    		for (int i=0;i<byteData.length;i++) {
    			String hex=Integer.toHexString(0xff & byteData[i]);
   	     		if(hex.length()==1) hexString.append('0');
   	     		hexString.append(hex);
    		        }
        	System.out.println("Hash : " + hexString.toString());
 
    }
}

I get errors and can't compile because of:
String prependZeros(b).

Been working on this for hours. Will report progress tomorrow if I get it to work. Good night for tonight

Originally Posted by Norm

Copy and paste here the full text of any error messages you want help with.

This is the error I get when I try to compile the above.

SHAHashingExample.java:11: error: ';' expected
	String prependZeros(b); { // number >= 0
                           ^
SHAHashingExample.java:11: error: not a statement
	String prependZeros(b); { // number >= 0
                            ^
SHAHashingExample.java:11: error: ';' expected
	String prependZeros(b); { // number >= 0
                             ^
3 errors

The 3 lines I posted earlier was an example coding to get the leading zeros to stay with original 16 digit hex number. I was going to to use an if/else but instead saw this as an example and though it would be better.

Once I figure out the Original: formatting to add the leading zeros, I then have to figure out how to make the hash become affected by the new numbers generated by the loop

Originally Posted by Junky

Do you have a question?

Always.

Is my prependzero string idea (from this post) a valid one to get the result I want with the leading zeros for the Original output? And if so, since Norm says I can't use "b" as a variable or I'm guessing create the string like I did, do I just need to use a new variable or do I need to phrase it differently? I'm more experimenting at this point to see what will even compile, and if it does, see what I get for output and then edit from there.

Originally Posted by Norm

Did you move the definiton for the prependZeros() outside of the method it was in?
What happened then?

I'll admit I feel I am still too new to it all and I can only guess your meaning. I assume you mean I need to close off my initial for statement with a "}", then I can take the result and run it through the new method? Even when I did that, I got the same error from this post.

Originally Posted by Norm

where did I say that?

See above. I took your meaning for method in a method differently.

Also if it hasn't been stated, the fact that you guys are having me find my own answer and see my own mistakes rather than just correcting my code and just giving it to me is something I really appreciate. Makes me feel like I am learning more.