der: fix encoding and decoding OIDs

make the code handle oids with a large second subidentifier (fixes #155)

make the code raise correct exception when the encoded multi-byte
subidentifier is missing the last byte

move OID test coverage to test_der module and extend it

update the OID generators in random DER generator to generate OIDs with
large second subidentifier

Author: tomato42

src/ecdsa/der.py

@@ -3,6 +3,7 @@
 import binascii
 import base64
 import warnings
+from itertools import chain
 from six import int2byte, b, text_type
 from ._compat import str_idx_as_int
 
@@ -97,12 +98,10 @@ def encode_octet_string(s):
 
 
 def encode_oid(first, second, *pieces):
-    assert first <= 2
-    assert second <= 39
-    encoded_pieces = [int2byte(40*first+second)] + [encode_number(p)
-                                                    for p in pieces]
-    body = b('').join(encoded_pieces)
-    return b('\x06') + encode_length(len(body)) + body
+    assert 0 <= first < 2 and 0 <= second <= 39 or first == 2 and 0 <= second
+    body = b''.join(chain([encode_number(40*first+second)],
+                          (encode_number(p) for p in pieces)))
+    return b'\x06' + encode_length(len(body)) + body
 
 
 def encode_sequence(*encoded_pieces):
@@ -157,20 +156,31 @@ def remove_octet_string(string):
 
 
 def remove_object(string):
+    if not string:
+        raise UnexpectedDER(
+            "Empty string does not encode an object identifier")
     if string[:1] != b"\x06":
         n = str_idx_as_int(string, 0)
         raise UnexpectedDER("wanted type 'object' (0x06), got 0x%02x" % n)
     length, lengthlength = read_length(string[1:])
     body = string[1+lengthlength:1+lengthlength+length]
     rest = string[1+lengthlength+length:]
+    if not body:
+        raise UnexpectedDER("Empty object identifier")
+    if len(body) != length:
+        raise UnexpectedDER(
+            "Length of object identifier longer than the provided buffer")
     numbers = []
     while body:
         n, ll = read_number(body)
         numbers.append(n)
         body = body[ll:]
     n0 = numbers.pop(0)
-    first = n0//40
-    second = n0-(40*first)
+    if n0 < 80:
+        first = n0 // 40
+    else:
+        first = 2
+    second = n0 - (40 * first)
     numbers.insert(0, first)
     numbers.insert(1, second)
     return tuple(numbers), rest
@@ -209,7 +219,7 @@ def read_number(string):
     llen = 0
     # base-128 big endian, with b7 set in all but the last byte
     while True:
-        if llen > len(string):
+        if llen >= len(string):
             raise UnexpectedDER("ran out of length bytes")
         number = number << 7
         d = str_idx_as_int(string, llen)

src/ecdsa/test_der.py

@@ -1,16 +1,20 @@
 
 # compatibility with Python 2.6, for that we need unittest2 package,
 # which is not available on 3.3 or 3.4
+import warnings
+from binascii import hexlify
 try:
     import unittest2 as unittest
 except ImportError:
     import unittest
-from .der import remove_integer, UnexpectedDER, read_length, encode_bitstring,\
-        remove_bitstring
 from six import b
+import hypothesis.strategies as st
+from hypothesis import given, example
 import pytest
-import warnings
 from ._compat import str_idx_as_int
+from .curves import NIST256p, NIST224p
+from .der import remove_integer, UnexpectedDER, read_length, encode_bitstring,\
+        remove_bitstring, remove_object, encode_oid
 
 
 class TestRemoveInteger(unittest.TestCase):
@@ -242,3 +246,131 @@ def test_bytes(self):
 
     def test_bytearray(self):
         self.assertEqual(115, str_idx_as_int(bytearray(b'str'), 0))
+
+
+class TestEncodeOid(unittest.TestCase):
+    def test_pub_key_oid(self):
+        oid_ecPublicKey = encode_oid(1, 2, 840, 10045, 2, 1)
+        self.assertEqual(hexlify(oid_ecPublicKey), b("06072a8648ce3d0201"))
+
+    def test_nist224p_oid(self):
+        self.assertEqual(hexlify(NIST224p.encoded_oid), b("06052b81040021"))
+
+    def test_nist256p_oid(self):
+        self.assertEqual(hexlify(NIST256p.encoded_oid),
+                         b"06082a8648ce3d030107")
+
+    def test_large_second_subid(self):
+        # from X.690, section 8.19.5
+        oid = encode_oid(2, 999, 3)
+        self.assertEqual(oid, b'\x06\x03\x88\x37\x03')
+
+    def test_with_two_subids(self):
+        oid = encode_oid(2, 999)
+        self.assertEqual(oid, b'\x06\x02\x88\x37')
+
+    def test_zero_zero(self):
+        oid = encode_oid(0, 0)
+        self.assertEqual(oid, b'\x06\x01\x00')
+
+    def test_with_wrong_types(self):
+        with self.assertRaises((TypeError, AssertionError)):
+            encode_oid(0, None)
+
+    def test_with_small_first_large_second(self):
+        with self.assertRaises(AssertionError):
+            encode_oid(1, 40)
+
+    def test_small_first_max_second(self):
+        oid = encode_oid(1, 39)
+        self.assertEqual(oid, b'\x06\x01\x4f')
+
+    def test_with_invalid_first(self):
+        with self.assertRaises(AssertionError):
+            encode_oid(3, 39)
+
+
+class TestRemoveObject(unittest.TestCase):
+    @classmethod
+    def setUpClass(cls):
+        cls.oid_ecPublicKey = encode_oid(1, 2, 840, 10045, 2, 1)
+
+    def test_pub_key_oid(self):
+        oid, rest = remove_object(self.oid_ecPublicKey)
+        self.assertEqual(rest, b'')
+        self.assertEqual(oid, (1, 2, 840, 10045, 2, 1))
+
+    def test_with_extra_bytes(self):
+        oid, rest = remove_object(self.oid_ecPublicKey + b'more')
+        self.assertEqual(rest, b'more')
+        self.assertEqual(oid, (1, 2, 840, 10045, 2, 1))
+
+    def test_with_large_second_subid(self):
+        # from X.690, section 8.19.5
+        oid, rest = remove_object(b'\x06\x03\x88\x37\x03')
+        self.assertEqual(rest, b'')
+        self.assertEqual(oid, (2, 999, 3))
+
+    def test_with_missing_last_byte_of_multi_byte(self):
+        with self.assertRaises(UnexpectedDER):
+            remove_object(b'\x06\x03\x88\x37\x83')
+
+    def test_with_two_subids(self):
+        oid, rest = remove_object(b'\x06\x02\x88\x37')
+        self.assertEqual(rest, b'')
+        self.assertEqual(oid, (2, 999))
+
+    def test_zero_zero(self):
+        oid, rest = remove_object(b'\x06\x01\x00')
+        self.assertEqual(rest, b'')
+        self.assertEqual(oid, (0, 0))
+
+    def test_empty_string(self):
+        with self.assertRaises(UnexpectedDER):
+            remove_object(b'')
+
+    def test_missing_length(self):
+        with self.assertRaises(UnexpectedDER):
+            remove_object(b'\x06')
+
+    def test_empty_oid(self):
+        with self.assertRaises(UnexpectedDER):
+            remove_object(b'\x06\x00')
+
+    def test_empty_oid_overflow(self):
+        with self.assertRaises(UnexpectedDER):
+            remove_object(b'\x06\x01')
+
+    def test_with_wrong_type(self):
+        with self.assertRaises(UnexpectedDER):
+            remove_object(b'\x04\x02\x88\x37')
+
+    def test_with_too_long_length(self):
+        with self.assertRaises(UnexpectedDER):
+            remove_object(b'\x06\x03\x88\x37')
+
+
+@st.composite
+def st_oid(draw, max_value=2**512, max_size=50):
+    """
+    Hypothesis strategy that returns valid OBJECT IDENTIFIERs as tuples
+
+    :param max_value: maximum value of any single sub-identifier
+    :param max_size: maximum length of the generated OID
+    """
+    first = draw(st.integers(min_value=0, max_value=2))
+    if first < 2:
+        second = draw(st.integers(min_value=0, max_value=39))
+    else:
+        second = draw(st.integers(min_value=0, max_value=max_value))
+    rest = draw(st.lists(st.integers(min_value=0, max_value=max_value),
+                         max_size=max_size))
+    return (first, second) + tuple(rest)
+
+
+@given(st_oid())
+def test_oids(ids):
+    encoded_oid = encode_oid(*ids)
+    decoded_oid, rest = remove_object(encoded_oid)
+    assert rest == b''
+    assert decoded_oid == ids

src/ecdsa/test_malformed_sigs.py

@@ -220,7 +220,10 @@ def st_der_oid(draw):
     Hypothesis strategy that returns DER OBJECT IDENTIFIER objects.
     """
     first = draw(st.integers(min_value=0, max_value=2))
-    second = draw(st.integers(min_value=0, max_value=39))
+    if first < 2:
+        second = draw(st.integers(min_value=0, max_value=39))
+    else:
+        second = draw(st.integers(min_value=0, max_value=2**512))
     rest = draw(st.lists(st.integers(min_value=0, max_value=2**512),
                          max_size=50))
     return encode_oid(first, second, *rest)

src/ecdsa/test_pyecdsa.py

@@ -952,17 +952,6 @@ def do_test_to_openssl(self, curve):
 
 
 class DER(unittest.TestCase):
-    def test_oids(self):
-        oid_ecPublicKey = der.encode_oid(1, 2, 840, 10045, 2, 1)
-        self.assertEqual(hexlify(oid_ecPublicKey), b("06072a8648ce3d0201"))
-        self.assertEqual(hexlify(NIST224p.encoded_oid), b("06052b81040021"))
-        self.assertEqual(hexlify(NIST256p.encoded_oid),
-                         b("06082a8648ce3d030107"))
-        x = oid_ecPublicKey + b("more")
-        x1, rest = der.remove_object(x)
-        self.assertEqual(x1, (1, 2, 840, 10045, 2, 1))
-        self.assertEqual(rest, b("more"))
-
     def test_integer(self):
         self.assertEqual(der.encode_integer(0), b("\x02\x01\x00"))
         self.assertEqual(der.encode_integer(1), b("\x02\x01\x01"))