Day: July 31, 2014

Apple’s Authentication Scheme and “Backdoors” Discussion

I’ve heard a number of people make an argument about Apple’s authentication front-ending the services I’ve described in my paper, including the “file relay” service, which has opened up a discussion about the technical definition of a backdoor. The primary concern I’m hearing, including from Apple, is that the user has to authenticate before having access to this service, which one would normally expect would preclude a service from being a backdoor by some (but not all) definitions. This is a valid point, and in fact I acknowledge this thoroughly in my paper. Let me explain, however, why this argument about authentication is more complicated and subtle than it seems.

Most authentication schemes are encapsulated from weakest to strongest, and are also isolated from one another; certain credentials get you into certain systems, but not into others. You may have a separate password for Twitter, Facebook, or other accounts, and they only interoperate if you’re using a single sign-on mechanism (for example, OAuth) to use that same set of credentials on other sites. If one gets stolen, then, only the services that are associated with those credentials can be accessed. Those authentication mechanisms are often protected with even stronger authentication systems. For example, your password might be stored on Apple’s keychain, which is protected with an encryption that is tied directly to your desktop password. Your entire disk might also be encrypted using full disk encryption, which protects the keychain (and all of your other data) with yet another (usually stronger) password. So you end up with a hierarchy of authentication mechanisms that get protected by stronger authentication mechanisms, and sometimes even stronger ones on top of that. Apple’s authentication scheme for iOS, however, is the opposite of this, where the strongest forms of authentication are protected by the weakest – creating a significant security problem in their design. The way Apple has designed the iOS authentication scheme is that the weakest forms of authentication have complete control to bypass the stronger forms of authentication. This allows services like file relay, which bypasses backup encryption, to be accessed with the weakest authentication mechanisms (PIN or pair record), when end-users are relying on the stronger “backup encryption password” to protect them.

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Oxygen Forensics: Latest Forensics Tool to Exploit Apple’s “Diagnostic Service” to Bypass Encryption

While Apple’s claims may be that a key subject of my talk, “Identifying Backdoors, Attack Points, and Surveillance Mechanisms in iOS Devices” (com.apple.mobile.file_relay) is for diagnostics, a recent announcement from the makers of the fantastic Oxygen Forensics suite shows strong evidence that law enforcement forensics is continuing to take every legal technical option available to Read More