Fix for key parse error in tpm2_objects

Signed-off-by: Isaac Matthews <isaac.matthews@hpe.com>

Author: Isaac-Matthews

keylime/tpm/tpm2_objects.py

@@ -285,11 +285,14 @@ def pubkey_parms_from_tpm2b_public(
     (_, sym_parms) = _extract_tpm2b(public[8:])
     # Ignore the non-asym-alg parameters
     (sym_alg,) = struct.unpack(">H", sym_parms[0:2])
+    (scheme_alg,) = struct.unpack(">H", sym_parms[2:4])
     # Ignore the sym_mode and keybits (4 bytes), possibly symmetric (2) and sign
     #  scheme (2)
-    to_skip = 4 + 2  # sym_mode, keybits and sign scheme
+    to_skip = 4  # sym_mode, keybits
     if sym_alg != TPM2_ALG_NULL:
         to_skip = to_skip + 2
+    if scheme_alg != TPM2_ALG_NULL:
+        to_skip = to_skip + 2
     asym_parms = sym_parms[to_skip:]
 
     # Handle fields

keylime/tpm/tpm2_objects_test.py

@@ -262,6 +262,21 @@ def test_pubkey_from_tpm2b_public_ec(self) -> None:
         self.assertEqual(new_ec_pubkey_n.x, correct_ec_pubkey_n.x)
         self.assertEqual(new_ec_pubkey_n.y, correct_ec_pubkey_n.y)
 
+    def test_pubkey_from_tpm2b_public_rsa_2(self) -> None:
+        # This key has Null set for the RSA scheme algorithm
+        test_pubkey_bytes = base64.b64decode(
+            "ATYAAQALAAQA8gAgrWs6IoT9aYoHEL9cwbm98V4lMuP2AfpLk6ao+o3leeoAEAAQCA"
+            "AAAAAAAQCUcktf2f6TOoVE94USfvExBIRumw5AOD2ahxDLXvYgTZoCEfIo4B1y/9o5"
+            "4aKs8eclm1ez1huCcSklaI07MQnSFv+YgmMsmGd9CQNe0b5uL9nGXDDHVEUeRERj/i"
+            "ZU82KEiXMYGs/8RfocrdFihsSKD/Xmgary+HU1HwkxWWPHYtFRLTlQgrqKJ1CckUaf"
+            "BHKyWvjjRLEhZC0YOZWAtbGN3bOJZ3FzBV21lx7e7RsBxBwUhQrRPbWh6UTb/lKBn8"
+            "pQgRLqb/wB5m99O7HzpKIy/trAQDnalPg2izgt7MByesMwTpJ0KGlwo69xus/UaE9a"
+            "apMZTnYR6W2mM2H6vrKl"
+        )
+        new_rsa_pubkey, name_alg = pubkey_parms_from_tpm2b_public(test_pubkey_bytes)
+        self.assertIsInstance(new_rsa_pubkey, rsa.RSAPublicKey)
+        self.assertEqual(name_alg, TPM_ALG_SHA256)
+
     def test_pubkey_from_tpm2b_public_ec_without_encryption(self) -> None:
         new_ec_pubkey = pubkey_from_tpm2b_public(
             bytes.fromhex(