Comment Re:Plausible deniability is better (Score 1) 203
They don't usually do this at a border check, but if they use a forensics terminal it's not running the OS, they basically do a backdoor boot and look at what the hardware reports.
The key point here is that data's security isn't enforced by the OS, but rather by the encryption algorithm itself. A non-OS forensics terminal would see the raw contents of the hard drive, which is to say, blocks of random-looking bytes that might be encrypted data or might just be truly random; without the corresponding password, there is no way to to tell.
Without any password (and assuming a robust encryption implementation), that's as far as they'd get. With a password, they'd be able to decrypt the blocks associated with that password and view the files for that account, but not any of the other blocks/accounts.
At that point, the FBI's nerds might well suspect that there are other accounts on the phone that they don't know about, but short of coercing the phone's owner into providing additional passwords, that's as far as they could get.