TPM2: Added CertifyEx and encodeCertifyEx (#211)

* TPM2: Added CertifyEx and encodeCertifyEx which differ from Certify and encodeCertify in that they take the scheme to be used as an additional argument. Signed-off-by: El Mostafa IDRASSI <[email protected]> * Fixed typo * Rename parentAuth and ownerAuth to objectAuth and signerAuth respectively. Signed-off-by: El Mostafa IDRASSI <[email protected]> * Update Certify documentation to explain it makes use of the hardcoded signing scheme {AlgRSASSA, AlgSHA256}. * Pack AlgNull with no following hash alg in case of AlgNull scheme, and add TODO comment. * Comment formatting and other requested changes. Signed-off-by: El Mostafa IDRASSI <[email protected]> * Replace all occurrences of tpmtSigScheme with SigScheme. Add CertifyEx tests for both RSASSA/SHA256 and ALG_NULL cases. * Better implementation of TestCertifyEx with all cases. Signed-off-by: El Mostafa IDRASSI <[email protected]> * Requested changes implemented.
google · Oct 13, 2020 · 6aef8a0 · 6aef8a0
1 parent ad82e86
commit 6aef8a0
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Showing 3 changed files with 110 additions and 15 deletions.
diff --git a/tpm2/structures.go b/tpm2/structures.go
@@ -619,11 +619,6 @@ func (p Private) Encode() ([]byte, error) {
 	return tpmutil.Pack(p)
 }
 
-type tpmtSigScheme struct {
-	Scheme Algorithm
-	Hash   Algorithm
-}
-
 // AttestationData contains data attested by TPM commands (like Certify).
 type AttestationData struct {
 	Magic                uint32

diff --git a/tpm2/test/tpm2_test.go b/tpm2/test/tpm2_test.go
@@ -575,6 +575,61 @@ func TestCertify(t *testing.T) {
 	})
 }
 
+func TestCertifyEx(t *testing.T) {
+	rw := openTPM(t)
+	defer rw.Close()
+
+	restrictedKeySignerFlags := FlagSignerDefault
+	unrestrictedKeySignerFlags := FlagSign | FlagFixedTPM | FlagFixedParent | FlagSensitiveDataOrigin | FlagUserWithAuth
+	testCases := []struct {
+		description  string
+		attributes   KeyProp
+		keyScheme    SigScheme
+		passedScheme SigScheme
+		shouldPass   bool
+	}{
+		{"Null-SHA1", unrestrictedKeySignerFlags, SigScheme{Alg: AlgNull}, SigScheme{Alg: AlgRSASSA, Hash: AlgSHA1}, true},
+		{"Null-SHA256", unrestrictedKeySignerFlags, SigScheme{Alg: AlgNull}, SigScheme{Alg: AlgRSASSA, Hash: AlgSHA256}, true},
+		{"Null-Null", unrestrictedKeySignerFlags, SigScheme{Alg: AlgNull}, SigScheme{Alg: AlgNull}, false},
+		{"SHA256-Null", restrictedKeySignerFlags, SigScheme{Alg: AlgRSASSA, Hash: AlgSHA256}, SigScheme{Alg: AlgNull}, true},
+		{"SHA256-SHA256", restrictedKeySignerFlags, SigScheme{Alg: AlgRSASSA, Hash: AlgSHA256}, SigScheme{Alg: AlgRSASSA, Hash: AlgSHA256}, true},
+		{"SHA256-SHA1", restrictedKeySignerFlags, SigScheme{Alg: AlgRSASSA, Hash: AlgSHA256}, SigScheme{Alg: AlgRSASSA, Hash: AlgSHA1}, false},
+	}
+
+	for _, testCase := range testCases {
+		params := Public{
+			Type:       AlgRSA,
+			NameAlg:    AlgSHA256,
+			Attributes: testCase.attributes,
+			RSAParameters: &RSAParams{
+				Sign:    &testCase.keyScheme,
+				KeyBits: 2048,
+			},
+		}
+
+		t.Run(testCase.description, func(t *testing.T) {
+			signerHandle, _, err := CreatePrimary(rw, HandleOwner, PCRSelection{}, emptyPassword, defaultPassword, params)
+			if err != nil {
+				t.Fatalf("CreatePrimary(signer) failed: %s", err)
+			}
+			defer FlushContext(rw, signerHandle)
+
+			subjectHandle, _, err := CreatePrimary(rw, HandlePlatform, PCRSelection{}, emptyPassword, defaultPassword, params)
+			if err != nil {
+				t.Fatalf("CreatePrimary(subject) failed: %s", err)
+			}
+			defer FlushContext(rw, subjectHandle)
+
+			_, _, err = CertifyEx(rw, defaultPassword, defaultPassword, subjectHandle, signerHandle, nil, testCase.passedScheme)
+			if err != nil && testCase.shouldPass {
+				t.Errorf("CertifyEx expected to succeed but failed: %s", err)
+			} else if err == nil && !testCase.shouldPass {
+				t.Errorf("CertifyEx expected to fail but succeeded")
+			}
+		})
+	}
+}
+
 func TestCertifyExternalKey(t *testing.T) {
 	rw := openTPM(t)
 	defer rw.Close()

diff --git a/tpm2/tpm2.go b/tpm2/tpm2.go
@@ -1550,24 +1550,51 @@ func Sign(rw io.ReadWriter, key tpmutil.Handle, password string, digest []byte,
 	return SignWithSession(rw, HandlePasswordSession, key, password, digest, validation, sigScheme)
 }
 
-func encodeCertify(parentAuth, ownerAuth string, object, signer tpmutil.Handle, qualifyingData tpmutil.U16Bytes) ([]byte, error) {
+func encodeCertify(objectAuth, signerAuth string, object, signer tpmutil.Handle, qualifyingData tpmutil.U16Bytes) ([]byte, error) {
 	ha, err := tpmutil.Pack(object, signer)
 	if err != nil {
 		return nil, err
 	}
 
-	auth, err := encodeAuthArea(AuthCommand{Session: HandlePasswordSession, Attributes: AttrContinueSession, Auth: []byte(parentAuth)}, AuthCommand{Session: HandlePasswordSession, Attributes: AttrContinueSession, Auth: []byte(ownerAuth)})
+	auth, err := encodeAuthArea(AuthCommand{Session: HandlePasswordSession, Attributes: AttrContinueSession, Auth: []byte(objectAuth)}, AuthCommand{Session: HandlePasswordSession, Attributes: AttrContinueSession, Auth: []byte(signerAuth)})
 	if err != nil {
 		return nil, err
 	}
 
-	scheme := tpmtSigScheme{AlgRSASSA, AlgSHA256}
+	scheme := SigScheme{Alg: AlgRSASSA, Hash: AlgSHA256}
 	// Use signing key's scheme.
-	params, err := tpmutil.Pack(qualifyingData, scheme)
+	s, err := scheme.encode()
 	if err != nil {
 		return nil, err
 	}
-	return concat(ha, auth, params)
+	data, err := tpmutil.Pack(qualifyingData)
+	if err != nil {
+		return nil, err
+	}
+	return concat(ha, auth, data, s)
+}
+
+// This function differs from encodeCertify in that it takes the scheme to be used as an additional argument.
+func encodeCertifyEx(objectAuth, signerAuth string, object, signer tpmutil.Handle, qualifyingData tpmutil.U16Bytes, scheme SigScheme) ([]byte, error) {
+	ha, err := tpmutil.Pack(object, signer)
+	if err != nil {
+		return nil, err
+	}
+
+	auth, err := encodeAuthArea(AuthCommand{Session: HandlePasswordSession, Attributes: AttrContinueSession, Auth: []byte(objectAuth)}, AuthCommand{Session: HandlePasswordSession, Attributes: AttrContinueSession, Auth: []byte(signerAuth)})
+	if err != nil {
+		return nil, err
+	}
+
+	s, err := scheme.encode()
+	if err != nil {
+		return nil, err
+	}
+	data, err := tpmutil.Pack(qualifyingData)
+	if err != nil {
+		return nil, err
+	}
+	return concat(ha, auth, data, s)
 }
 
 func decodeCertify(resp []byte) ([]byte, []byte, error) {
@@ -1604,14 +1631,32 @@ func decodeCertify(resp []byte) ([]byte, []byte, error) {
 }
 
 // Certify generates a signature of a loaded TPM object with a signing key
-// signer. Returned values are: attestation data (TPMS_ATTEST), signature and
-// error, if any.
-func Certify(rw io.ReadWriter, parentAuth, ownerAuth string, object, signer tpmutil.Handle, qualifyingData []byte) ([]byte, []byte, error) {
-	Cmd, err := encodeCertify(parentAuth, ownerAuth, object, signer, qualifyingData)
+// signer. This function calls encodeCertify which makes use of the hardcoded
+// signing scheme {AlgRSASSA, AlgSHA256}. Returned values are: attestation data (TPMS_ATTEST),
+// signature and error, if any.
+func Certify(rw io.ReadWriter, objectAuth, signerAuth string, object, signer tpmutil.Handle, qualifyingData []byte) ([]byte, []byte, error) {
+	cmd, err := encodeCertify(objectAuth, signerAuth, object, signer, qualifyingData)
+	if err != nil {
+		return nil, nil, err
+	}
+	resp, err := runCommand(rw, TagSessions, CmdCertify, tpmutil.RawBytes(cmd))
+	if err != nil {
+		return nil, nil, err
+	}
+	return decodeCertify(resp)
+}
+
+// CertifyEx generates a signature of a loaded TPM object with a signing key
+// signer. This function differs from Certify in that it takes the scheme
+// to be used as an additional argument and calls encodeCertifyEx instead
+// of encodeCertify. Returned values are: attestation data (TPMS_ATTEST),
+// signature and error, if any.
+func CertifyEx(rw io.ReadWriter, objectAuth, signerAuth string, object, signer tpmutil.Handle, qualifyingData []byte, scheme SigScheme) ([]byte, []byte, error) {
+	cmd, err := encodeCertifyEx(objectAuth, signerAuth, object, signer, qualifyingData, scheme)
 	if err != nil {
 		return nil, nil, err
 	}
-	resp, err := runCommand(rw, TagSessions, CmdCertify, tpmutil.RawBytes(Cmd))
+	resp, err := runCommand(rw, TagSessions, CmdCertify, tpmutil.RawBytes(cmd))
 	if err != nil {
 		return nil, nil, err
 	}