How to Authenticate MD5

Question

I creating MD5 this way:

public void encrypeUsername(String sessionid)
    {
        byte[] defaultBytes = sessionid.getBytes();
        try
        {
            MessageDigest algorithm = MessageDigest.getInstance("MD5");
            algorithm.reset();
            algorithm.update(defaultBytes);
            byte messageDigest[] = algorithm.digest();

            StringBuffer hexString = new StringBuffer();
            for (int i = 0; i < messageDigest.length; i++)
            {
                hexString.append(Integer.toHexString(0xFF & messageDigest[i]));
            }
            System.out.println("sessionid " + sessionid + " md5 version is " + hexString.toString());
        }
        catch (Exception e)
        {
            e.printStackTrace();
        }



    }

for input 123456 we get MD5: e1adc3949ba59abbe56e057f2f883e

I want to create another method to authenticate the result.

For example if i give an input of e1adc3949ba59abbe56e057f2f883e and "123456" then I get as result: true/false.

Any idea how to achieve this?

thanks, ray.

Answer 1

String pass = "123456";
String secret = "e1adc3949ba59abbe56e057f2f883e";
if encrypeUsername(pass).equals(secret) System.out.printl("ok!")

Remember that md5 is one-way. It is hard* to get the password from the secret back again.

(*)Not so hard nowerdays for weak passwords.