At 19:01 -0500 on 11/15/03, R. A. Hettinga wrote:

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Status: U Date: Sat, 15 Nov 2003 13:03:33 +0100 From: "Ralf-P. Weinmann" <weinmann@cdc.informatik.tu-darmstadt.de> To: Nicko van Someren <nicko@ncipher.com> Cc: mac_crypto@vmeng.com, "R. A. Hettinga" <rah@shipwright.com> Subject: Re: [Mac_crypto] MacOS X (Panther) FileVault

On Thu, Nov 13, 2003 at 01:15:03PM +0000, Nicko van Someren wrote:

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This is basically correct. FileVault uses an auto-mounting version of the encrypted disk image facility that was in 10.2, tweaked to allow the image to be opened even before your main key chain is available (since the key chain is stored inside your home directory). The standard encrypted image format uses a random key stored on your key chain, which is itself encrypted with a salted and hashed copy of the keychain pass phrase, which defaults to your login password. My suspicion is that for the FileVault there is some other key chain file in the system folder which stores the key for decrypting your home directory disk image and that the pass phrase for that is just your login password.

Ahhhh... So FileVault actually is just a marketing term for the encrypted disk images! Thanks for the explanation! I just hope my login password can be longer than 8 characters then.

Yes/no. When your not logged in your home folder is stored as an encrypted DiskImage. In addition part of enabling FileVault was a complete rework of how login authentication was handled, part of which included removing the 8 char limitation. For the record, apple has always allowed passwords longer than 8 char, prior to 10.3, however, only the first 8 char were used to log you in, though the other characters were used to unlock your keychain.

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File Vault will automatically expand or contract the disk image at certain points. It creates a new image, copies everything over, and deletes the old image.

Yup, it essentially does an "hdiutil compact" command when you log out.

Do you know whether the source code to hdiutil and hdid respectively its 10.3 kernel equivalent is available? I can't seem to find it in the Darwin 7.0 public source.

No they are not. Apple considers DiskImages to be a proprietary competitive advantage.

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I don't know what mode of AES-128 it uses.

I believe that it uses counter mode, since it's efficient when doing random access to the encrypted data.

Of course counter mode would be ideally suited for this application. The question is whether the people at Apple implementing this feature knew this :)

It is a virtual certainty that Apple used Security.framework which includes a variety of algorithms (including AES) and secure/peer reviewed operation modes. I believe the security framework is open source, and in fact based on a broader standard (CDSA). If you'd like to know for certain I'd suggest you email dts@apple.com and/or file a bug report at bugreporter.apple.com (requires free registration) on the documentation. -- __________________________________________ Arguing with an engineer is like wrestling with a pig in mud. After a while, you realize the pig is enjoying it. __________________________________________ Kevin Elliott <mailto:kelliott@mac.com> ICQ#23758827 AIM ID: teargo iChatAV: kelliott@mac.com (video chat available) __________________________________________