We can view an existing Message Authentication Code (MAC) as a Carter-Wegman MAC in spite of the fact it may not have been designed as one. This will make the analysis easier than it has been when considered from other viewpoints. In this paper, we can look PMAC with two keys as a Carter-Wegman MAC and get a simple security proof for it. Using this viewpoint to look at PMAC, we will learn not only why the PMAC is such constructed, but also a new method of constructing MACs.