[SQLServer2005] I don't have a database master key, I still can create a symmetric key. Why?

Question

When I don't have master key for AdventureWorks, I still can do this:

 

CREATE SYMMETRIC KEY Test

WITH ALGORITHM = DES

ENCRYPTION BY PASSWORD = 'abc123.';

 

What if I create a symmetric key without database master key?

I read MSDN but it doesn't say about this.