This is an excellent article describing the techincal issue. This, however, is not why Tim Cook is furious. The reason he is mad is because the government’s framing of the issue is disengenuous at best. They don’t really need access to this phone. They would like it, but they do not need it. It is however, a hot button emotional issue they can use as leverage counting on the American people to disregard the complex technical and privacy issues and have a binary view with regard to terrorism (you are either a good guy or a bad guy). This emotional approach while creating a crisis is how they move their agenda forward because a reasoned arguement would fail.