On Feb 21, 2008, at 6:40 PM, Ali, Saqib wrote:
i think in most cases tamper-resistant is sufficient
Er, what do TPMs have to do with this at all? TPMs are not tamper-
proof hardware FDE devices. They're somewhat tamper-proof (in
practice, I wouldn't depend on it) non-volatile storage for small
amounts of sensitive data, such as encryption keys. But as long as
it's software that's driving your FD encryption, you need to have your
keys in RAM.
So, either:
* The TPM is used in 'basic' mode, where its only purpose is to
provide a measure of tamper-resistance to the boot path, and as
long as no boot-time tampering is detected, the FDE key will be
loaded into RAM automatically,
or,
* The TPM requires explicit authentication (e.g. by password or
smart card) before releasing the key, in which case a successful
authentication will load the FDE key in RAM.
If the machine is running and the FDE in use -- which is the entire
premise behind this attack -- both TPM use cases are just as
vulnerable. TPMs are a red herring in this discussion, unless the FDE
was actually offloading the crypto operations to it. This is not a
supported mode of operation for any widely-deployed FDE system that
I'm familiar with.
So, is anyone else as amused as I am that Apple can release an EFI
firmware update to zeroize MacBook Air memory at boot-time, turning
the heretofore widely-decried inability to upgrade that laptop's RAM
-- due to the chips being soldered to the motherboard -- into an
advantage, and making the Air the laptop of choice for discriminating,
fashion-aware, security-conscious professionals the world over?
--
Ivan Krstić <[EMAIL PROTECTED]> | http://radian.org
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