DigestUtils 和 MessageDigest 的 MD5 结果不同

Question

I have tried to use java.security.MessageDigest or org.apache.commons.codec.digest.DigestUtils to do md5, but there comes out different results.

The sample code as below:

public static void main( String[] args )
{
    System.out.println("MessageDigest: " +  MD5("12345") );

    MessageDigest md5Digest = DigestUtils.getMd5Digest();
    System.out.println("MD5Hex with digest: " + DigestUtils.md5Hex(md5Digest.digest("12345".getBytes())));

    System.out.println("MD5Hex: " + DigestUtils.md5Hex("12345"));
}

public final static String MD5(String s) {
    char hexDigits[]={'0','1','2','3','4','5','6','7','8','9','A','B','C','D','E','F'};       

    try {
        byte[] btInput = s.getBytes();
        // 獲得MD5摘要算法的 MessageDigest 對象
        MessageDigest mdInst = MessageDigest.getInstance("MD5");
        // 使用指定的字節更新摘要
        mdInst.update(btInput);
        // 獲得密文
        byte[] md = mdInst.digest();
        // 把密文轉換成十六進制的字符串形式
        int j = md.length;
        char str[] = new char[j * 2];
        int k = 0;
        for (int i = 0; i < j; i++) {
            byte byte0 = md[i];

            str[k++] = hexDigits[byte0 >>> 4 & 0xf];
            str[k++] = hexDigits[byte0 & 0xf];
        }
        System.out.println();
        return new String(str);
    } catch (Exception e) {
        e.printStackTrace();
        return null;
    }
}

The results as below:

MessageDigest: 827CCB0EEA8A706C4C34A16891F84E7B
MD5Hex with digest: aad43635bbd353cef6ea6546093fa0c7
MD5Hex: 827ccb0eea8a706c4c34a16891f84e7b

If I have give md5Digest.digest() into DigestUtils.md5Hex, the result is different from MessageDigest. But if I just do md5Hex(), it will be the same. What's the different between this two way?

Thanks

Answer 1

When you are calling DigestUtils.md5Hex(md5Digest.digest("12345".getBytes()))) , you actually calculate the MD5 of the result of the previous MD5 calculation. Thus no wonder that double-MD5 differs from single MD5.