Add config struct for AttestPlatform(), to configure event log source (#118)

attest/attest.go

@@ -119,6 +119,9 @@ func (k *AIK) ActivateCredential(tpm *TPM, in EncryptedCredential) (secret []byt
 }
 
 // Quote returns a quote over the platform state, signed by the AIK.
+//
+// This is a low-level API. Consumers seeking to attest the state of the
+// platform should use tpm.AttestPlatform() instead.
 func (k *AIK) Quote(tpm *TPM, nonce []byte, alg HashAlg) (*Quote, error) {
 	return k.aik.quote(tpm.tpm, nonce, alg)
 }

attest/example_test.go

@@ -91,46 +91,22 @@ func ExampleAIK_credentialActivation() {
 	}
 }
 
-func ExampleAIK_quote() {
-	tpm, err := attest.OpenTPM(nil)
-	if err != nil {
-		log.Fatalf("Failed to open TPM: %v", err)
-	}
-	defer tpm.Close()
-
-	// Create a new AIK.
-	aik, err := tpm.NewAIK(nil)
-	if err != nil {
-		log.Fatalf("Failed to create AIK: %v", err)
-	}
-	defer aik.Close(tpm)
-
-	// The nonce would typically be provided by the server.
-	nonce := []byte{1, 2, 3, 4, 5, 6, 7, 8}
-
-	// Perform the quote & gather information necessary to verify it.
-	quote, err := aik.Quote(tpm, nonce, attest.HashSHA1)
-	if err != nil {
-		log.Fatalf("Failed to generate quote: %v", err)
-	}
-	pcrs, err := tpm.PCRs(attest.HashSHA1)
-	if err != nil {
-		log.Fatalf("Failed to collect PCR values: %v", err)
-	}
-	log.Printf("quote = %+v", quote)
-	log.Printf("PCRs = %+v", pcrs)
-}
-
 func TestExampleAIK(t *testing.T) {
 	if !*testExamples {
 		t.SkipNow()
 	}
 	ExampleAIK()
 	ExampleAIK_credentialActivation()
-	ExampleAIK_quote()
 }
 
-func ExampleAIKPublic_Verify() {
+func TestExampleTPM(t *testing.T) {
+	if !*testExamples {
+		t.SkipNow()
+	}
+	ExampleTPM_AttestPlatform()
+}
+
+func ExampleTPM_AttestPlatform() {
 	tpm, err := attest.OpenTPM(nil)
 	if err != nil {
 		log.Fatalf("Failed to open TPM: %v", err)
@@ -147,30 +123,27 @@ func ExampleAIKPublic_Verify() {
 	// The nonce would typically be provided by the server.
 	nonce := []byte{1, 2, 3, 4, 5, 6, 7, 8}
 
-	// Perform the quote & gather information necessary to verify it.
-	quote, err := aik.Quote(tpm, nonce, attest.HashSHA256)
+	// Perform an attestation against the state of the plaform. Usually, you
+	// would pass a nil config, and the event log would be read from the
+	// platform. To ensure this example runs on platforms without event logs,
+	// we pass a fake EventLog value.
+	att, err := tpm.AttestPlatform(aik, nonce, &attest.PlatformAttestConfig{
+		EventLog: []byte{0},
+	})
 	if err != nil {
-		log.Fatalf("Failed to generate quote: %v", err)
-	}
-	pcrs, err := tpm.PCRs(attest.HashSHA256)
-	if err != nil {
-		log.Fatalf("Failed to collect PCR values: %v", err)
+		log.Fatalf("Failed to attest the platform state: %v", err)
 	}
 
-	// Construct an AIKPublic struct from the parameters of the key.
+	// Construct an AIKPublic struct from the parameters of the key. This
+	// will be used to  verify the quote signatures.
 	pub, err := attest.ParseAIKPublic(tpm.Version(), aik.AttestationParameters().Public)
 	if err != nil {
 		log.Fatalf("Failed to parse AIK public: %v", err)
 	}
 
-	if err := pub.Verify(*quote, pcrs, nonce); err != nil {
-		log.Fatalf("Verification failed: %v", err)
+	for i, q := range att.Quotes {
+		if err := pub.Verify(q, att.PCRs, nonce); err != nil {
+			log.Fatalf("quote[%d] verification failed: %v", i, err)
+		}
 	}
 }
-
-func TestExampleAIKPublic(t *testing.T) {
-	if !*testExamples {
-		t.SkipNow()
-	}
-	ExampleAIKPublic_Verify()
-}

attest/tpm.go

@@ -298,6 +298,9 @@ func (t *TPM) LoadAIK(opaqueBlob []byte) (*AIK, error) {
 }
 
 // MeasurementLog returns the present value of the System Measurement Log.
+//
+// This is a low-level API. Consumers seeking to attest the state of the
+// platform should use tpm.AttestPlatform() instead.
 func (t *TPM) MeasurementLog() ([]byte, error) {
 	return t.tpm.measurementLog()
 }
@@ -310,9 +313,8 @@ func (t *TPM) NewAIK(opts *AIKConfig) (*AIK, error) {
 // PCRs returns the present value of Platform Configuration Registers with
 // the given digest algorithm.
 //
-// Use ParseEventLog to determine which algorithm to use to match the values
-// present in the event log. It's not always guarenteed that a system with TPM
-// 2.0 will extend PCRs with SHA256 digests.
+// This is a low-level API. Consumers seeking to attest the state of the
+// platform should use tpm.AttestPlatform() instead.
 func (t *TPM) PCRs(alg HashAlg) ([]PCR, error) {
 	return t.tpm.pcrs(alg)
 }
@@ -358,16 +360,36 @@ func (t *TPM) attestPlatform(aik *AIK, nonce []byte, eventLog []byte) (*Platform
 	return &out, nil
 }
 
+// PlatformAttestConfig configures how attestations are generated through
+// tpm.AttestPlatform().
+type PlatformAttestConfig struct {
+	// If non-nil, the raw event log will be read from EventLog
+	// instead of being obtained from the running system.
+	EventLog []byte
+}
+
 // AttestPlatform computes the set of information necessary to attest the
 // state of the platform. For TPM 2.0 devices, AttestPlatform will attempt
 // to read both SHA1 & SHA256 PCR banks and quote both of them, so bugs in
 // platform firmware which break replay for one PCR bank can be mitigated
 // using the other.
-func (t *TPM) AttestPlatform(aik *AIK, nonce []byte) (*PlatformParameters, error) {
-	el, err := t.MeasurementLog()
-	if err != nil {
-		return nil, fmt.Errorf("failed to read event log: %v", err)
+// The provided config, if not nil, can be used to configure aspects of the
+// platform attestation.
+func (t *TPM) AttestPlatform(aik *AIK, nonce []byte, config *PlatformAttestConfig) (*PlatformParameters, error) {
+	if config == nil {
+		config = &PlatformAttestConfig{}
 	}
+
+	var el []byte
+	if config.EventLog != nil {
+		el = config.EventLog
+	} else {
+		var err error
+		if el, err = t.MeasurementLog(); err != nil {
+			return nil, fmt.Errorf("failed to read event log: %v", err)
+		}
+	}
+
 	return t.attestPlatform(aik, nonce, el)
 }