try to support pkcs8 v2 format pem file for EdDSA (#281)

* try to support pkcs8 v2 format pem file

Author: Myse1f

src/ecdsa/keys.py

@@ -1124,10 +1124,16 @@ def from_der(cls, string, hashfunc=sha1, valid_curve_encodings=None):
                         "Non NULL parameters for a EdDSA key"
                     )
                 key_str_der, s = der.remove_octet_string(s)
-                if s:
-                    raise der.UnexpectedDER(
-                        "trailing junk inside the privateKey"
-                    )
+
+                # As RFC5958 describe, there are may be optional Attributes
+                # and Publickey. Don't raise error if something after
+                # Privatekey
+
+                # TODO parse attributes or validate publickey
+                # if s:
+                #     raise der.UnexpectedDER(
+                #         "trailing junk inside the privateKey"
+                #     )
                 key_str, s = der.remove_octet_string(key_str_der)
                 if s:
                     raise der.UnexpectedDER(

src/ecdsa/test_keys.py

@@ -927,3 +927,13 @@ def test_VerifyingKey_inequality_with_different_secret_points():
     sk2 = SigningKey.from_secret_exponent(3, BRAINPOOLP160r1)
 
     assert sk1.verifying_key != sk2.verifying_key
+
+
+def test_SigningKey_from_pem_pkcs8v2_EdDSA():
+    pem = """-----BEGIN PRIVATE KEY-----
+    MFMCAQEwBQYDK2VwBCIEICc2F2ag1n1QP0jY+g9qWx5sDkx0s/HdNi3cSRHw+zsI
+    oSMDIQA+HQ2xCif8a/LMWR2m5HaCm5I2pKe/cc8OiRANMHxjKQ==
+    -----END PRIVATE KEY-----"""
+
+    sk = SigningKey.from_pem(pem)
+    assert sk.curve == Ed25519