BigInteger.toString method is deleting leading 0

Question

I am trying to generate MD5 sum using MessageDigest. And i am having following code.

byte[] md5sum = digest.digest();
BigInteger bigInt = new BigInteger(1, md5sum);
output = bigInt.toString(16);

This returns not 32 character string but a 31 character string 8611c0b0832bce5a19ceee626a403a7

Expected String is 08611c0b0832bce5a19ceee626a403a7

Leading 0 is missing in the output.

I tried the other method

byte[] md5sum = digest.digest();
output = new String(Hex.encodeHex(md5sum));

And the output is as expected.

I checked the doc and Integer.toString does the conversion according to it

The digit-to-character mapping provided by Character.forDigit is used, and a minus sign is prepended if appropriate.

and in Character.forDigit methos

The digit argument is valid if 0 <=digit < radix.

Can some one tell me how two methods are different and why leading 0 is deleted?

Are you saying that `BigInteger.toString()` is *supposed* to output a leading zero? — Gabe, Apr 23 '12 at 06:31
All i am asking is why toString is removing the leading 0. ? — Dheeraj Joshi, Apr 23 '12 at 06:32
Yeah well and i get a negative vote as if it is not useful. Boohoo — Dheeraj Joshi, Apr 23 '12 at 06:34
I don't understand what you're asking. How is `toString` supposed to know that you're expecting a leading 0? `BigInteger` stores just a number; it doesn't know how many leading zeroes you're expecting. — Gabe, Apr 23 '12 at 06:35
Think of it another way: what would you expect from `new BigInteger("27").toString()`? How many leading zeros? — yshavit, Apr 23 '12 at 07:30

score 22 · Accepted Answer · answered Apr 23 '12 at 06:33

I would personally avoid using BigInteger to convert binary data to text. That's not really what it's there for, even if it can be used for that. There's loads of code available to convert a byte[] to its hex representation - e.g. using Apache Commons Codec or a simple single method:

private static final char[] HEX_DIGITS = "0123456789ABCDEF".toCharArray();
public static String toHex(byte[] data) {
    char[] chars = new char[data.length * 2];
    for (int i = 0; i < data.length; i++) {
        chars[i * 2] = HEX_DIGITS[(data[i] >> 4) & 0xf];
        chars[i * 2 + 1] = HEX_DIGITS[data[i] & 0xf];
    }
    return new String(chars);
}

score 13 · Answer 2 · edited Oct 21 '21 at 09:58

13

String.format("%064X", new BigInteger(1, ByteArray);

where

0 - zero leading sign
64 - string length
X - Uppercase
ByteArray - The ByteArray on which you want to run this operation

edited Oct 21 '21 at 09:58

ChiralCarbon

347
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11

answered Jan 12 '16 at 14:39

Gorets

2,434
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27
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@Andro it's link to Cipher.getInstance("HMAC"); – Gorets Feb 16 '17 at 12:09

score 9 · Answer 3 · answered Apr 23 '12 at 06:33

It's deleted because the leading zero is not significant, according to BigInteger. There is no difference between 27 and 000000000027.

If you want a specific length, you'll have to force it yourself, with something like:

output = ("00000000000000000000000000000000"+output).substring(output.length());

(kludgy though that is).

user1689394 · Answer 4 · 2012-09-26T16:04:27.530

2

The deleted zero is replaced using this code:

MessageDigest digest = MessageDigest.getInstance("MD5");
digest.reset();
digest.update(output.getBytes());
byte[] outDigest = digest.digest();
BigInteger outBigInt = new BigInteger(1,outDigest);
output = outBigInt.toString(16);
    while (output.length() < 32){
    output = "0"+output;
    }

loop will account for as many leading zeros as needed

edited Sep 26 '12 at 16:04

answered Sep 26 '12 at 14:54

user1689394

331
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I think Dheeraj was looking for reasons for the deleted zero. Not a way to get it back. Also, your code does not work the way you think it does. – allingeek Sep 27 '12 at 06:44
Sorry, you are right, but my code does work sending the correct md5 checksum to my server. – user1689394 Sep 27 '12 at 14:07

score -2 · Answer 5 · edited Feb 11 '18 at 18:59

-2

MessageDigest m=MessageDigest.getInstance("MD5");
m.update(PlainText.getBytes(),0,PlainText.length());
String M1=new BigInteger(1,m.digest()).toString(16);      
return M1;

edited Feb 11 '18 at 18:59

Wai Ha Lee

8,598
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answered Feb 11 '18 at 17:33

Aram

1

Downvoted because your answer is not correctly formatted and it does not contain any explanations whatsoever. – Sync Feb 11 '18 at 17:42
I've fixed the formatting, but you still need to explain the code. Somebody [flagged your answer for deletion](https://stackoverflow.com/review/low-quality-posts/18790340), but [code-only answers are not low-quality](https://meta.stackoverflow.com/a/358757/1364007). Your answer appears to be an attempt to answer the question, so should not have been flagged. Does it deserve a downvote? Quite possibly - I can't comment on its correctness or usefulness - but I personally have not downvoted. – Wai Ha Lee Feb 11 '18 at 19:02

BigInteger.toString method is deleting leading 0

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