Re: [Trustedjava-support] How to compute Hash over PCRs without TPM

[Account I. <mud...@ho...>]

Hi Ronald,

Thanks for your reply. I used jTSS 0.6 to get it done quite simply.

TcPcrCompositeInfoLong expectedPcrComposite = new 
TcPcrCompositeInfoLong(24);

expectedPcrComposite.selectPcrIndexEx(16, 
TcTssConstants.TSS_PCRS_DIRECTION_RELEASE);
expectedPcrComposite.setPcrValue(16, expectedPCR);
TcBlobData expectedCompositeDigest = 
expectedPcrComposite.getPcrCompositeHash();

And a question for my understanding: Conceptually, is it allowed/possible to 
create context object on
a machine which does not have TPM?

Regards.
Mudassar.

--------------------------------------------------
From: "Ronald Tögl" <ron...@ia...>
Sent: Wednesday, October 06, 2010 4:20 PM
To: "Account Info" <mud...@ho...>
Subject: Re: [Trustedjava-support] How to compute Hash over PCRs without TPM

> Hello Mudassar,
>
> This is a code fragment on how to do quote validation. I guess it is 
> pretty self-explanatory.
> As of jTSS 0.6 you can also create the PCR CompositeInfo(Long|Short) 
> objects offline from the implementation classes in package
> iaik.tc.tss.impl.java.tsp.
>
> hth, Ronald
>
>
>     try {
>             TcBlobData dataBlob = TcBlobData.newByteArray(dataToValidate
>                     .getData());
>             TcTpmQuoteInfo2 quoteInfo = new TcTpmQuoteInfo2(dataBlob);
>
>             TcTpmPcrInfoShort pcrInfo = quoteInfo.getInfoShort();
>             TcTpmCompositeHash compositeHash = 
> pcrInfo.getDigestAtRelease();
>             TcBlobData digestAtRelease = compositeHash.getDigest();
>
>             TcIPcrComposite expectedComp = ((TPMContextImpl) context_)
>                     .getTcIContext().createPcrCompositeObject(
>                             TcTssConstants.TSS_PCRS_STRUCT_INFO_SHORT);
>
>             int[] expectedIndices = expectedValues.getValueIndices();
>
>             for (int i = 0; i < expectedIndices.length; i++) {
>                 expectedComp.setPcrValue(expectedIndices[i], TcBlobData
>                         .newByteArray(expectedValues.getPCRValue(
>                                 expectedIndices[i]).getBytes()));
>             }
>
>             TcBlobData expectedDigestAtRelease = expectedComp
>                     .getPcrCompositeHash();
>
>             if (!Arrays.equals(digestAtRelease.asByteArray(),
>                     expectedDigestAtRelease.asByteArray())) {
>                 return false;
>             }
>
>             Signature sig = Signature.getInstance("SHA1withRSA");
>             sig.initVerify(identityKey);
>             sig.update(dataToValidate.getData());
>             boolean valid = 
> sig.verify(dataToValidate.getValidationData());
>
>             return valid;
>
>         } catch (TcTssException e) {
>
>
> On 10/06/2010 04:04 PM, Account Info wrote:
>> Hi,
>> I have the same problem as listed in the following attached post by Till
>> Bentz. The answer to this question refers to another post with
>> Subject: "Re: Recompute PRC based on SML and TPM_Quote problem" and
>> Message-ID:<469...@ia...>  posted on Date: Mon, 16 Jul 
>> 2007
>> 09:28:06 +0200. But this message is blank.
>>
>> I could not find any code in tests which could compute the hash over the
>> quoted PCRs WITHOUT USING TPM (i.e. TcIPcrComposite object). I guess that 
>> I
>> should do something as follows:
>>
>> TcTpmPcrInfoShort pcrInfo = new TcTpmPcrInfoShort(); // short because PCR 
>> 16
>> intended
>>
>> TcTpmPcrSelection pcrSelection = new TcTpmPcrSelection();
>> // 1. how to say that PCR 16 should be selected ???????
>>
>> TcTpmPcrValue pcrValue = new TcTpmPcrValue();
>> // 2. how to put some value at PCR 16 ??????
>>
>> pcrInfo.setPcrSelection(pcrSelection); // if done in step 1
>> // 3. How to associate PCR value with pcrinfo ?????
>>
>> pcrInfo.getDigestAtRelease().getDigest();// It will give the required 
>> digest
>> having set the expected value in PCR 16
>>
>> Regards
>>
>> Mudassar.
>>
>>
>> ----------------------------------------------------------------------------------------------
>>
>> Hello,
>>
>> I try to do a tpm_quote. I managed to set the relevant pPCRs, the 
>> validation
>> information and actually execute the
>> quote call.
>>
>> My problem is now that i somehow want to check the quote. How can I do 
>> that
>> on a PC without a TPM. As far as I understood the quote process computes 
>> a
>> hash over the quoted PCRs and stores it in 
>> TcTpmQuoteInfo.getDigestValue()
>>
>> I have the values of each quoted PCR, but how do I manually recompute 
>> that
>> value so I can check the quote?
>>
>> Thanks.
>>
>
>