java.lang.ClassCastException: [B > cannot be cast to java.lang.String

Seems the password column of your database is a type mapped as a String in Java (varchar most probably). So hibernate cannot convert your byte array to a String.

You can change your lines to something like:

 String digest = new String(md.digest());
 String query = "SELECT L FROM Login AS L WHERE L.email=? AND L.password=?";
 Object[] parameters = { login.getEmail(), digest };

But it probably won't work as the digest will most certainly contain bytes not mappable to chars regardless of the encoding. You should probably use a base64 encoding to map you binary blob to a String.

Another solution will be to change your dabase scheme and make the password field a binary rather than a varchar.

In both cases you need to know how the password field is inserted in the database.

Some remarks on your code:

I find strange that you check the password by selecting a row from your database with both the username and the password. I'd though more logical to select using only the user and then validate the supplied password against the one returned on the database.

You use a hash function to ensure your password won't be stored in plain text in the database. That's good. However your scheme has a big flaw: if several users have the same password then the hashed password will be the same in the database. So if you have access to the database and know the password of one user it'll be really easy to find all the users sharing this password. In order to build something more secure you should use a password encoding scheme that include some salt.

looks like you're [passing a byte array where a string was required.

try { login.getEmail(), new String(digest) }; instead of { login.getEmail(), digest };

refer http://download.oracle.com/javase/1.4.2/docs/api/java/lang/String.html#String%28byte[]%29