Good day.
1. I am attempting to demonstrate that PCR contents shall remain identical
should there be no changes in BOTH :
a) current contents of PCR[i] AND,
b) SHA1 of measurement,
found in the Tspi_TPM_PcrExtend () function which operates as follows:
Extend to PCR[i] the SHA1( current contents of PCR[i] || SHA1 of measurement).
2. In my case here, I have chosen PCRs -15 & 16 for measurement extenstion. The
measurement mentioned in no. 1a and 1b. above are two entities in the following
forms:
a) memory address in the form of hex i.e. 0x08049d49 and,
b) contents of WORD at a memory address above i.e. 0xffffffff.
3. What I had attempted here is : using Tspi_TPM_PcrExtend () , generate SHA1
for 2.a) & b) , subsequently extend to PCR-15 & 16 respectively to produce the
following output:
PCR-15: 99 43 90 F1 2A EC 55 02 0D 58 9B 17 58 30 DA C7 FE 51 63 F9
PCR-16: 26 2D 49 5B 9D D5 83 CE DC CE 7E 7B DC 93 95 28 1D 06 0E 0E
4. I am facing a problem now- the contents of PCRs 15 & 16 changes despite 2a)
& 2b) remained constant, which
is not what I expected. I need PCRs 15 & 16 not to change should 2a) & 2b)
remained constant.
5. My request for any kind assistance are as follows:
a) Where in the Trousers source can the code for generating the SHA1 of
measurement i.e. 2a) and b) be found?
b) Where in the Trousers source can the code for SHA1( current contents of
PCR[i] || SHA1 of measurement) be found?
6. I suspect that the problem might lie in either 5a) or 5b) or both .Hence I
wish to implement a hash comparison code to check the SHA1 generated in both
5a) and 5b) . Only upon any changes in 5a) then 5b) will be executed and then
extended to PCRs 15 & 16. Hopefully, the PCR contents remained identical.
7. Would no.6 be able to solve my problem or could anyone kindly advise with a
better solution?
Pls have my thousand thanks and appreciation in advance.
Rgds
jyteh.
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