Alex Besogonov wrote: [skip] >>> As far as I understand - no. >> Actually - it is. >> Check the "TCG PC Client Specific Implementation Specification for >> Conventional >> Bios" or "TCG PC Specific Implementation Specification" at >> https://www.trustedcomputinggroup.org/specs/PCClient/ >> and look for CRTM (Core Root of Trust for Measurement) > Yes, BIOS is a root of trust, but not the Core Root. BIOS itself is > checked before execution (pages 20 and onwards in the "TCG PC Client > Specific Implementation Specification for Conventional Bios" spec), > even before dynamic memory is initialized. Well on page 32 they list two options, how to implement the CRTM: BIOS Boot Block or entire BIOS Since the BIOS is usually updateable, it seems that most manufacturers opt for BIOS Boot Block, which I assume will be something like: "lets put the first sector of the BIOS in ROM" (of course it might be something else completely, but I doubt it)
>>> First, I don't think it's possible to implement SHA-1 hashing in MBR - >>> there's probably just not enough space left in 512-byte code segment >>> for that. >> I am very sure of that. > Well, I spoke phcoder on Jabber - there might be a way to do this. > He's going to investigate it. Sounds interesting. >>> Second, the only safe action non TPM-aware MBR can perform if it >>> detects tampering is just shutting down hard. Everything else is >>> dangerous. >> Yeah, but an attacker could patch that out too. > Not if we first measure the MBR. It can be done without any > TPM-specific code in the MBR if I'm not very mistaken. Could you elaborate on that? E.g. where do you measure the MBR from? > PS: thanks for detailed explanation! Sure, glad I could help! Greets, Jan
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