Question

I am using following code block to generate MD5 hashes:

public static String encode(String data) throws Exception {

    /* Check the validity of data */
    if (data == null || data.isEmpty()) {
        throw new IllegalArgumentException("Null value provided for "
                + "MD5 Encoding");
    }

    /* Get the instances for a given digest scheme MD5 or SHA */
    MessageDigest m = MessageDigest.getInstance("MD5");

    /* Generate the digest. Pass in the text as bytes, length to the
     * bytes(offset) to be hashed; for full string pass 0 to text.length()
     */
    m.update(data.getBytes(), 0, data.length());

    /* Get the String representation of hash bytes, create a big integer
     * out of bytes then convert it into hex value (16 as input to
     * toString method)
     */
    String digest = new BigInteger(1, m.digest()).toString(16);

    return digest;
}

When I run the above code segment with String data as [12, B006GQIIEM, MH-ANT2000], the output is a 31 character hash – 268d43a823933c9dafaa4ac0e756d6a.

Is there any problem with the MD5 hash function or there is some problem in the code above?

Answer 1

The only issue in your code is when MSB is less than Ox10, the result hash string will only have 31 bytes, instead of 32 bytes, missing the leading zero.

Create your md5 string in this way:

            byte messageDigest[] = m.digest();

            hexString = new StringBuffer();
            for (int i=0;i<messageDigest.length;i++) {
                String hex=Integer.toHexString(0xFF & messageDigest[i]);
                if(hex.length()==1)
                    hexString.append('0');

                hexString.append(hex);
            }