Protecting yourself from the Wily Hacker
First, a few words: I'm going to use the XML-RPC api to Blogger as an example of potential theoretical confusion. This isn't to imply that there's anything wrong with either XML-RPC, the Blogger API, or Blogger; The Blogger API is no less secure than your bank account, your email account, or your home security system. What the Blogger API represents here is one of a million examples of the kind of pervasive thinking regarding how to keep things secure. I'm positing that there is another way of making systems secure.
We can start by understanding the potential causes of vulnerabilities. The capability secure crowd will argue, and I agree, that many (if not all) of these problems are caused by the unbundling of the ability to perform an action with the action's location. What this means is that anybody can perform any action as long as they can confuse the system into thinking that they're allowed to perform that action. Usernames and passwords are a good example. If I can figure out Ev's blogger password, I can then post to his weblog as him. Capability-security would prevent me from posing as Ev and therefore prevent me from posting to his weblogs. Let's bust out some graphs:
In traditional systems, you have the location of a service, such as http://plant.blogger.com/api/RPC2.blogger.newPost(), and your authority to perform an action, your username and password.
In a capability-secure system, knowing the location of a service means you have the authority to use the service. the service would appear as http://plant.blogger.com/
# — 01 October, 2002