Correctly check that the scalar matches the point when importing an E…

…CC private key
Legrandin · May 15, 2023 · 2b11e5b · 2b11e5b
1 parent d64618b
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Showing 3 changed files with 13 additions and 2 deletions.
diff --git a/Changelog.rst b/Changelog.rst
@@ -13,6 +13,7 @@ New features
 ---------------
 * GH#722: ``nonce`` attribute was not correctly set for XChaCha20_Poly1305 ciphers. Thanks to Liam Haber.
 * GH#739: OID encoding for arc 2 didn't accept children larger than 39. Thanks to James.
+* Correctly check that the scalar matches the point when importing an ECC private key.
 
 3.17.0 (29 January 2023)
 ++++++++++++++++++++++++++

diff --git a/lib/Crypto/PublicKey/ECC.py b/lib/Crypto/PublicKey/ECC.py
@@ -1396,8 +1396,8 @@ def _import_rfc5915_der(encoded, passphrase, curve_oid=None):
     d = Integer.from_bytes(scalar_bytes)
 
     # Decode public key (if any)
-    if len(private_key) == 4:
-        public_key_enc = DerBitString(explicit=1).decode(private_key[3]).value
+    if len(private_key) > 2:
+        public_key_enc = DerBitString(explicit=1).decode(private_key[-1]).value
         public_key = _import_public_der(public_key_enc, curve_oid=curve_oid)
         point_x = public_key.pointQ.x
         point_y = public_key.pointQ.y

diff --git a/lib/Crypto/SelfTest/PublicKey/test_import_ECC.py b/lib/Crypto/SelfTest/PublicKey/test_import_ECC.py
@@ -183,6 +183,16 @@ class TestImport(unittest.TestCase):
     def test_empty(self):
         self.assertRaises(ValueError, ECC.import_key, b"")
 
+    def test_mismatch(self):
+        # The private key does not match the public key
+        mismatch = """-----BEGIN PRIVATE KEY-----
+MIG2AgEAMBAGByqGSM49AgEGBSuBBAAiBIGeMIGbAgEBBDAAAAAAAAAAAAAAAAAA
+AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAJChZANiAAQarFRaqflo
+I+d61SRvU8Za2EurxtW20eZzca7dnNYMYf3boIkDuAUU7FfO7l0/4iGzzvfUinng
+o4N+LZfQYcTxmdwlkWOrfzCjtHDix6EznPO/LlxTsV+zfTJ/ijTjeXk=
+-----END PRIVATE KEY-----"""
+        self.assertRaises(ValueError, ECC.import_key, mismatch)
+
 
 class TestImport_P192(unittest.TestCase):