tpm2-quote-tools

This is a simple tool to read and manipulate TPM2 quotes. It was written while experimenting with tpmfail. It supports the following commands:

• Validating an EC keypair, where the pub key is serialized according to RFC5480 and the priv key is provided with its integer representation
• Validating a TPM quote, given a PCR file reading
• Tampering a quote, based on a modified PCR file

It assumes to be working with a NIST P-256 Curve.

P-256 assumption

The assumption to be working with P-256 comes from the fact that the SubjectPublicKeyInfo structure produced by tpm2-tools (at least version 4.0-rc2, which was the one I used to extract ak.pub and experiment with tpmfail) doesn't seem to be fully compliant with PKIX and cannot be unmarshalled with ParsePKIXPublicKey.

PKIX (RFC5280) requires the following format:

type publicKeyInfo struct {
    Raw       asn1.RawContent
    Algorithm pkix.AlgorithmIdentifier
    PublicKey asn1.BitString
}

ParsePKIXPublicKey is failing with "failed to parse ECDSA parameters as named curve", which seems to be deriving from trying to extract the curve type from Algorithm.Parameters.FullBytes in the pkix.AlgorithmIdentifier object. In particular, from x509.go:

case ECDSA:
        paramsData := keyData.Algorithm.Parameters.FullBytes
        namedCurveOID := new(asn1.ObjectIdentifier)
        rest, err := asn1.Unmarshal(paramsData, namedCurveOID)
        if err != nil {
            return nil, errors.New("x509: failed to parse ECDSA parameters as named curve")
        }

where namedCurveOID is eventually used to build the right curse, e.g. elliptic.P256(). This problem should be coming solely from the tooling, but I haven't investigated it further.

Validate ECDSA keypair

 ./tpm2-quote-tools validateKeypair -privKey 123.... --pubKeyPath ak.pub
{
  "X": 83480738740571363643324029101585429304839996582896622312114556128429276170770,
  "Y": 31332509983944448906473882585486887031546885874433110787215501175612644198303,
  "Priv": 123...,
  "Valid": true
 }

Validate quote

validateQuote command does only basic validation of the signature of the quote and the PCR register digest.

./tpm2-quote-tools -debug validateQuote  -pcrReadPath pcrs -quotePath quote.out -sigPath sig.out -pubKeyPath ak.pub  -privKey 123...
{
 "Magic": "0xff544347",
 "StType": "0x8018",
 "QualifiedSigner": {
  "Size": 34,
  "Name": "0x000bc0cae8498b1672f3a59465d1c7550186e7bb854ebe1c73d32a63fcd381be7116"
 },
 "ExtraData": {
  "Size": 3,
  "Buffer": "0xabc123"
 },
 "ClockInfo": {
  "Clock": 579462030,
  "ResetCount": 6,
  "RestartCount": 0,
  "YesNo": 1
 },
 "FirmwareVersion": "...",
 "QuoteInfo": {
  "PcrSelect": {
   "Count": 1,
   "PcrSelection": {
    "Hash": 11,
    "SizeofSelect": 3,
    "PcrSelect": "0,1,2,3"
   }
  },
  "PcrDigest": {
   "Size": 32,
   "Buffer": "0xb54daa5a817ddda5e6ff7a533dd639b9294c8ebd163d15a09142d046c3c4dca7"
  }
 }
}
DEBU[0000] sha256sum calculated from quote: 0x36508eca394ce64c4eca8eca1557137db8b185465054044c192f2ca00afe066d 
DEBU[0000] reading signature file at sig.out      
DEBU[0000] ecdsa signature, r: 111363902270336560310064823465267952429958334463429462940652152104343902580681, s: 38244762622328238605270552925184855082267863709725176991353603896491389561246 
DEBU[0000] validating quote signature with ecPub, X: 83480738740571363643324029101585429304839996582896622312114556128429276170770, Y: 31332509983944448906473882585486887031546885874433110787215501175612644198303 
DEBU[0000] signature OK                                 
DEBU[0000] validating pcr hash against pcrs
DEBU[0000] reading pcr file at pcrs
DEBU[0000] pcr file: found [0] : [...] 
DEBU[0000] pcr file: found [1] : [...] 
[...]
DEBU[0000] digest match: 0xb54daa5a817ddda5e6ff7a533dd639b9294c8ebd163d15a09142d046c3c4dca7 == 0xb54daa5a817ddda5e6ff7a533dd639b9294c8ebd163d15a09142d046c3c4dca7 
OK

Tamper quote

Tamper quote can be used to modify the PCR digest in an existing quote, based on a modified pcr file, and re-calculate the signature.

./tpm2-quote-tools -debug forgeQuote -pcrReadPath pcrs.forged -privKey 123...
2358 -pubKeyPath ak.pub -quotePath quote.out -sigOutPath sigForged.out -quoteOutPath quoteForged.out
DEBU[0000] reading pcr file at pcrs.forged              
DEBU[0000] pcr file: found [0] : [...] 
DEBU[0000] pcr file: found [1] : [...] 
[...]
DEBU[0000] signing 0x3f3b56ce242c9daaaa59812bdf9f30421048e333f4e44089860748e7769edb89 
DEBU[0000] calculated signature, r: 108360506779383934389187539972624208747061077985692324975265347036204466096619, s: 111915589499407566637626902186915864276073926565433784980906979210501747227395

The tampered quote can be then validated with validateQuote command:

./tpm2-quote-tools -debug validateQuote  -pcrReadPath pcrs.forged -quotePath quoteForged.out -sigPath sigForged.out -pubKeyPath data/ak.pub -privKey 123...               
{
  "Magic": "0xff544347",
  "StType": "0x8018",
  "QualifiedSigner": {
   "Size": 34,
   "Name": "0x000bc0cae8498b1672f3a59465d1c7550186e7bb854ebe1c73d32a63fcd381be7116"
  },
  "ExtraData": {
   "Size": 3,
   "Buffer": "0xabc123"
  },
  "ClockInfo": {
   "Clock": 579462030,
   "ResetCount": 6,
   "RestartCount": 0,
   "YesNo": 1
  },
  "FirmwareVersion": "0x49000444a01164",
  "QuoteInfo": {
   "PcrSelect": {
    "Count": 1,
    "PcrSelection": {
     "Hash": 11,
     "SizeofSelect": 3,
     "PcrSelect": "0,1,2,3"
    }
   },
   "PcrDigest": {
    "Size": 32,
    "Buffer": "0x2987d731e24966251ceceab7d7102124cd8e2bc44c4b9c6104e33d7d07e961ef"
   }
  }
 }
DEBU[0000] sha256sum calculated from quote: 0x3f3b56ce242c9daaaa59812bdf9f30421048e333f4e44089860748e7769edb89 
DEBU[0000] reading signature file at sigForged.out      
DEBU[0000] ecdsa signature, r: 108360506779383934389187539972624208747061077985692324975265347036204466096619, s: 111915589499407566637626902186915864276073926565433784980906979210501747227395 
DEBU[0000] validating quote signature with ecPub, X: 83480738740571363643324029101585429304839996582896622312114556128429276170770, Y: 31332509983944448906473882585486887031546885874433110787215501175612644198303 
DEBU[0000] signature OK                                 
DEBU[0000] validating pcr hash against pcrs.forged      
DEBU[0000] reading pcr file at pcrs.forged              
DEBU[0000] pcr file: found [0] : [...] 
DEBU[0000] pcr file: found [1] : [...] 
DEBU[0000] digest match: 0x2987d731e24966251ceceab7d7102124cd8e2bc44c4b9c6104e33d7d07e961ef == 0x2987d731e24966251ceceab7d7102124cd8e2bc44c4b9c6104e33d7d07e961ef 
OK