It's not specifically secured on the wire (even though one might expect a hardware attack to be quite costly).
HOWEVER, PCRs are not "set" to a value. Instead they are "extended" by a value. PCRs get initialized with a set value and when they are extended they do a sha1 of their old and the OS-provided value to calculate the new value... A PCR state thereby contains a hash-chain of all previous "extend" operations. (except for the special cases of resettable PCRs, that can be detected by having a different initial state)
Also authentication is secured "over the i2c/lpc-wire" via challenge-nonce sha1-hmac authentication.
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Re: That I2C bus sounds ripe for interception.
Date: 2013-05-08 09:05 am (UTC)HOWEVER, PCRs are not "set" to a value. Instead they are "extended" by a value. PCRs get initialized with a set value and when they are extended they do a sha1 of their old and the OS-provided value to calculate the new value... A PCR state thereby contains a hash-chain of all previous "extend" operations. (except for the special cases of resettable PCRs, that can be detected by having a different initial state)
Also authentication is secured "over the i2c/lpc-wire" via challenge-nonce sha1-hmac authentication.
Cheers,
Andreas