Checking MD5 of a file

Question

I am getting an error while trying to check the MD5 hash of a file.

The file, notice.txt has the following contents:

My name is sanjay yadav . i am in btech computer science .>>

When I checked online with onlineMD5.com it gave the MD5 as: 90F450C33FAC09630D344CBA9BF80471.

My program output is:

My name is sanjay yadav . i am in btech computer science .
Read 58 bytes
d41d8cd98f00b204e9800998ecf8427e

Here's my code:

import java.io.*;
import java.math.BigInteger;
import java.security.DigestException;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

public class MsgDgt {
    public static void main(String[] args) throws IOException, DigestException, NoSuchAlgorithmException {

        FileInputStream inputstream = null;
        byte[] mybyte = new byte[1024];

        inputstream = new FileInputStream("e://notice.txt");
        int total = 0;
        int nRead = 0;
        MessageDigest md = MessageDigest.getInstance("MD5");
        while ((nRead = inputstream.read(mybyte)) != -1) {
            System.out.println(new String(mybyte));
            total += nRead;
            md.update(mybyte, 0, nRead);
        }

        System.out.println("Read " + total + " bytes");
        md.digest();
        System.out.println(new BigInteger(1, md.digest()).toString(16));
    }
}

possible duplicate of [Getting a File's MD5 Checksum in Java](http://stackoverflow.com/questions/304268/getting-a-files-md5-checksum-in-java) — Simon, Jul 02 '13 at 06:07
I will not rely on that website now..i think the output 2f4c6a40682161e5b01c24d5aa896da0 is correct... you missed one zero in the last..(please Check it). The Content Was "My name is sanjay yadav . i am in btech computer science ." — Bitopan, Jul 02 '13 at 07:14

Jon Skeet · Accepted Answer · 2013-07-02T07:41:02.577

There's a bug in your code and I believe the online tool is giving the wrong answer. Here, you're currently computing the digest twice:

md.digest();
System.out.println(new BigInteger(1, md.digest()).toString(16));

Each time you call digest(), it resets the internal state. You should remove the first call to digest(). That then leaves you with this as the digest:

2f4c6a40682161e5b01c24d5aa896da0

That's the same result I get from C#, and I believe it to be correct. I don't know why the online checker is giving an incorrect result. (If you put it into the text part of the same site, it gives the right result.)

A couple of other points on your code though:

You're currently using the platform default encoding when converting the bytes to a string. I would strongly discourage you from doing that.
You're currently converting the whole buffer to a string, instead of only the bit you've read.
I don't like using BigInteger as a way of converting binary data to hex. You potentially need to pad it with 0s, and it's basically not what the class was designed for. Use a dedicated hex conversion class, e.g. from Apache Commons Codec (or various Stack Overflow answers which provide standalone classes for the purpose).
You're not closing your input stream. You should do so in a finally block, or using a try-with-resources statement in Java 7.

I will not rely on that website now..i think the output 2f4c6a40682161e5b01c24d5aa896da0 is correct... you missed one zero in the last..(please Check it). The Content Was "My name is sanjay yadav . i am in btech computer science ." — Bitopan, Jul 02 '13 at 07:04

Knossos · Answer 2 · 2013-07-02T06:21:09.880

0

I use this function:

public static String md5Hash(File file) {
    try {
        MessageDigest md = MessageDigest.getInstance("MD5");
        InputStream is = new FileInputStream(file);
        byte[] buffer = new byte[1024];

        try {
            is = new DigestInputStream(is, md);

            while (is.read(buffer) != -1) { }
        } finally {
            is.close();
        }

        byte[] digest = md.digest();

        BigInteger bigInt = new BigInteger(1, digest);
        String output = bigInt.toString(16);
        while (output.length() < 32) {
            output = "0" + output;
        }

        return output;
    } catch (NoSuchAlgorithmException e) {
        e.printStackTrace();
    } catch (FileNotFoundException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }

    return null;
}

edited Jul 02 '13 at 06:21

answered Jul 02 '13 at 06:06

Knossos

15,802
10
54
91

Why would you want to create a new byte array for each `read` call? It seems a little tortuous to me - as is using `BigInteger` for hex conversions (rather than code which is designed to convert a byte array to hex). The exception handling is worrying, too... – Jon Skeet Jul 02 '13 at 06:09
Actually, I am not sure about the whole function now to think about it. This was an example I found online. Although, I am not certain the problem with using BigInteger, what would you do instead? I completely agree with the byte array declaration. – Knossos Jul 02 '13 at 06:18
I'd either use something like Apache Commons Codec, or find an answer to one of the many "how do I convert bytes to hex" questions on Stack Overflow. – Jon Skeet Jul 02 '13 at 06:21
I will not rely on that website now..i think the output 2f4c6a40682161e5b01c24d5aa896da0 is correct... you missed one zero in the last..(please Check it). The Content Was "My name is sanjay yadav . i am in btech computer science ." – Bitopan Jul 02 '13 at 07:16

Checking MD5 of a file

2 Answers2