getting a negative value on md5

Question

Im trying to get an MD5 with java and I receive a negative value. Can an MD5 result in a negative value?

This is my code:

        MessageDigest md5 = MessageDigest.getInstance("MD5");
        byte[] sigBytes = md5.digest((sharedSecret+"api_key"+API_KEY).getBytes());
        api_sig = new BigInteger(sigBytes).toString(16);

Thank You.

Wow sorry, I shouldn't vote to close when I just woke up. – dee-see Feb 28 '12 at 11:28 — dee-see, Feb 28 '12 at 11:28

score 3 · Answer 1 · edited May 23 '17 at 12:12

3

new BigInteger(sigBytes) is interpreting your signature as a signed integer, so yes, it would be possible to get a negative number. If you want Your string to contain the hex representation of your md5 value, have a look at some of the answers here: How can I generate an MD5 hash?

edited May 23 '17 at 12:12

Community

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answered Feb 28 '12 at 11:27

jbowes

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Is `toString(16)` a bad way to get hex representation? – Ari M Feb 28 '12 at 16:41

score 1 · Answer 2 · edited May 23 '17 at 11:43

1

As jbowes alluded to, new BigInteger(sigBytes) is interpreting the signature as a signed integer (meaning the first bit denotes whether the number is positive or negative). If you want it to interpret the bytes as an unsigned number, you should use new BigInteger(1, sigBytes) instead.

edited May 23 '17 at 11:43

Community

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answered May 24 '13 at 18:02

Gili

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score 0 · Answer 3 · answered Feb 28 '12 at 11:35

I use following method to get right MD5 hash String (and it never gave me "negative" value):

public static String createMD5Hash(String input) {
    try {
        MessageDigest m = MessageDigest.getInstance("MD5");
        byte[] out = m.digest(input.getBytes());
        return new String(Base64.encodeBase64(out));
    } catch (NoSuchAlgorithmException e) {
        return null;
    }
}

Note that Base64 is class from apache commons:

import org.apache.commons.codec.binary.Base64;

getting a negative value on md5

3 Answers3