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I'm planning to buy a TPM module to bring more security in my system (GNU/Linux, dm-crypt/LUKS, SED) but I'm not sure with the big debate around it.

What are the (possible) privacy concerns in using a TPM chip ?
Can my keys or my datas be leaked to government agencies or criminals ?
Can my OS be infected using the firmware in the chip as an attack vector ?

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    What do you mean you're going to add a TPM chip to your computer? Does the motherboard come with support for that? – Neil Smithline Feb 20 '16 at 23:55
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    @NeilSmithline Assuming he knows what he's doing, he's probably looking into buying something like this. Yup, add-on TPM chips are a thing. – HopelessN00b Feb 21 '16 at 0:05
  • Edited. HopelessN00b is correct, my motherboard come with a support for a tpm module and I'm looking to buy one – jsxoepq Feb 21 '16 at 7:30
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The TPM compromising the OS is pretty unlikely. The chip talks to the host computer via a low-speed serial bus comparable to a serial port; the code handling data received on that port is much simpler than let's say USB-related code, so if someone wanted to own the machine they would rather use USB-based solutions (especially since you don't even have to exploit any vulnerabilities in USB-handling code as USB has a built-in vulnerability : it trusts any USB keyboard right away).

Now, whether the TPM is good at what it's supposed to be doing is a different issue. Personally I don't trust TPMs for full-disk encryption as the key is transmitted unencrypted over the LPC bus, so for someone with physical access to a machine (even turned off) all he has to do to own it is to connect a logic analyser to the LPC bus and grab the key from there. Once that's done the attacker defeated the FDE even though the machine was off, thanks to the TPM.

As far as other uses of the TPM where it generates and holds a secret key, it comes down to whether you trust the manufacturer to not have put in a secret command that would make the TPM spit out the key it was supposed to protect (or a "bug" that would allow running arbitrary code on the TPM), as well as trusting the manufacturer to have sufficiently hardened the chip against hardware attacks.

  • But in the case of dm-crypt/LUCKS the key is not stored plaintext in it, just the hash or I'm wrong ? Can Self Encrypting Drive protect against this ? And without physical access to my computer can this module leaks informations over internet or intranet ? – jsxoepq Feb 24 '16 at 11:08
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    @jsxoepq a TPM shouldn't have any reason to talk to the network; but of course it all comes down to how much you trust the manufacturer. Your system board's Ethernet port may have lines going to the TPM port and their "TPM" is actually evil and embeds their own Ethernet controller as well that will talk to the network and leak secrets that way. – André Borie Feb 24 '16 at 11:10
  • The embedded fTPM on Intel chips does not communicate over LPC and is entirely contained within the chipset. – forest Jun 5 '18 at 1:46

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