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Date: Tue, 10 Apr 2012 20:09:56 +0530
From: Dhiru Kholia <>
Subject: Re: Mac OS X keychains and FileVault

On Tue, Apr 10, 2012 at 12:01 PM, Dhiru Kholia <> wrote:
> On Mon, Apr 9, 2012 at 11:10 PM, Dhiru Kholia <> wrote:
>> I have implement a JtR plug-in for cracking Mac OS X Keychain
>> passwords based on extractkeychain-0.1.
> There is a bug in the current code which leads to large number of
> false positives. The problem is that only checking padding bytes is
> not enough to detect wrong passwords. Code to calculate and check
> HMACSHA1 check sum needs to be figured out and implemented to get rid
> of these false positives. extractkeychain-0.1 too does not implement
> this check.

There are two "enhancements" that can be done to ensure that the
user password is detected correctly as wrong or right. Both of these
check are described in BLOBFORMAT document.


The following checks need to be implemented in JtR plug-in.

10. Verify that SHA1HMAC(DSK, TEMP3) == SIG (using VerifyMac) if fail
then password is wrong.
11. Let DEK = Octets 20 though 44 of TEMP1
12. If DEK does not have odd parity in all octets then DBB is corrupt.
VerifyMac is used here :


Implementing these changes will require understanding securityd's
working (by compiling and debugging securityd). This will require a
Mac computer which I don't have access to. Can someone with a Mac take
over the development of Keychain JtR plug-in from here?


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