Java compare md5 with another md5 from another generator : not same value

Question

I can generate md5 with this function :

private void generateMd5() throws NoSuchAlgorithmException, IOException {
        MessageDigest md = MessageDigest.getInstance("MD5");
        byte[] hash = md.digest(pathFile.getBytes());
        nomGestionnaire.setText(String.valueOf(String.format("%032X", new BigInteger(1, hash))));

    }

My problem is when I compare my md5 generate with another md5 generator I don't have the same value. Is it normal ? It's like my generator doesn't generate a real md5 ?

Test with this file : aaa.txt (content : aaa)

My generator : A4FA953DB4BC7772E5AF67BD706B9110

other generator : 47bce5c74f589f4867dbd57e9ca9f808

EDIT :

FileChooser fileChooser = new FileChooser();
File selectedFile = new 
File(String.valueOf(fileChooser.showOpenDialog(primaryStage)));
nameFile = selectedFile.getName();
pathFile = selectedFile.getPath();

You are calculating the md5 of a String (the file path). My first suspect would be an encoding problem (i. e. the String can be represented by different byte sequences). Could you please add your input and the two generated md5 sums to your question? — , Jul 28 '20 at 14:47
(And yes, Java's md5 implementation is, in fact, "a real md5".) — , Jul 28 '20 at 14:49
@Software149735 Do you want to check/run the md5 checksum on the path to the file or do you want to check/run the md5 checksum on the content of the file? — Progman, Jul 28 '20 at 14:59
Does "pathFile" contain the file's path, or the file's content? — , Jul 28 '20 at 15:00
@Software149735 so there's your problem: you're comparing md5("aaa") to md5("C:\Users\Software149735\aaa.txt") or something like that. Of course those are not the same! — , Jul 28 '20 at 15:02
@Taschi: does the file path contain any non-ASCII characters (accented characters, emojis, non-latin characters?). There's a good chance that the fact that `String.getBytes()` uses the platform default encoding messes you up somehow. — Joachim Sauer, Jul 28 '20 at 15:02
@Software149735 Also check https://stackoverflow.com/questions/415953/how-can-i-generate-an-md5-hash — Progman, Jul 28 '20 at 15:03
@Progman I tried `String content = Files.readString(Paths.get(pathFile));` but the md5 code is different too : `7018899CA561F7826599F24E5448CFDE` — Software149735, Jul 28 '20 at 15:08

score 2 · Accepted Answer · answered Jul 28 '20 at 15:24

I guess there's some error on the input. Unfortunately the and file you provided is not complete. So I did I first wrote a Java method that does a basic md5. Then I did some forensics to guess and fix the code. Both deliver correct MD5: 47BCE5C74F589F4867DBD57E9CA9F808

    public static String getMD5(String filename)
        throws NoSuchAlgorithmException, IOException {
    MessageDigest md = MessageDigest.getInstance("MD5");
    md.update(Files.readAllBytes(Paths.get(filename)));
    byte[] digest = md.digest();
    String myChecksum = DatatypeConverter.printHexBinary(digest).toUpperCase();
    return myChecksum;
}



public static String generateMd5(String pathToFile) throws NoSuchAlgorithmException, IOException {
    MessageDigest md = MessageDigest.getInstance("MD5");
    byte[] hash = md.digest(Files.readAllBytes(Paths.get(pathToFile)));
    return String.valueOf(String.format("%032X", new BigInteger(1, hash)));
}

perfect ! it works ! thank you ! – Software149735 Jul 28 '20 at 16:42 — Software149735, Jul 28 '20 at 16:42

score 0 · Answer 2 · answered Jul 28 '20 at 15:21

I faced this problem before, it is probably an encoding problem (from that file path). I put it like this in my project, and it's working just fine since then. I'll provide you with a sample, so probably you get an idea from this:

public String hash(String stringToHash){
    MessageDigest messageDigest = MessageDigest.getInstance("MD5");
    // here you init the message digit singleton with the wanted algorithm
    messageDigest.update(stringToHash.getBytes());
    //now you updated it, with the bytes of your string
    byte[] digest = messageDigest.digest();
    String result = DatatypeConverter.printHexBinary(digest);
    // finally you converted the result (hex) to String (you hashed string)
    // you may want to use toLowerCase() so you make it case insensitive
    return result;
}

NOTE: you have many way to hash using md5, I really prefer using the Apache Commons as an easy way, you may want to check this out MD5 Hashing using Apache Commons. You also can do that using Google Guava : MD5 Hashing using Google Guava.

Java compare md5 with another md5 from another generator : not same value

2 Answers2