On Aug 15, 2008, at 10:33 AM, Jason Coco wrote:

On Aug 15, 2008, at 11:11 , Jeff Johnson wrote:

Jason,

See the following threads for some discussion of these issues:

http://lists.apple.com/archives/Macnetworkprog/2008/Apr/msg00033.html

http://lists.apple.com/archives/Xcode-users/2008/Jul/msg00283.html

Interesting... thanks, Jeff. So I guess the answer is for speed/non- sensitive cache data, maybe confstr(_CS_DARWIN_USER_CACHE_DIR, path, length) is the appropriate call... and maybe for data that may need to actually reside in the filevault, regardless of speed, the return value from the Cocoa call is more appropriate (~/ Library/Caches)?

That sounds reasonable.

I would like to point out a couple of interesting things, though...

1) ~/Library/Caches is world writable too... so as long as you're logged in, even if you have your filevault armed, you're still gonna be somewhat vulnerable to cache attacks.

This is incorrect, FileVault or not. Where do you get that idea?

2) The new temporary directory (returned the same by confstr (_CS_DARWIN_USER_TEMP_DIR,...) and NSTemporaryDirectory(...) is also outside the sphere of filevault /and/ your files there are not necessarily erased on log-out. I think it's cleaned up with the computer boots (although it may be deleted on shutdown, but I don't think so)... so if any sensitive information were written to the temp dir and the application relied on it being cleaned by the OS, that could be an issue too if
    your physical drive were compromised...

Too bad these aren't sysctl variables that could be set if security were more important to the user than performance... I checked the darwin source and the directories returned by confstr(...) are
hard-coded into libc...

/Jason

Frankly, I've come to the conclusion that while FileVault is a nice idea in theory, there's just no way for the FileVault user to protect from developers -- whether Apple or third parties -- writing files to the wrong place. Thankfully, it seems that we're finally getting some full disk encryption solutions for the Mac. There is at least one already on the market (Check Point), and apparently others are working on it too (e.g., PGP announced something, but it's currently vaporware, perhaps to stop people from buying Check Point).

-Jeff

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