Returns back the not extended sig decoding for der

Author: gstarovo

src/ecdsa/test_malformed_sigs.py

@@ -29,7 +29,7 @@
 
 from .keys import SigningKey
 from .keys import BadSignatureError
-from .util import number_to_string, sigencode_der, sigencode_der_sig_value_a, sigencode_string
+from .util import number_to_string, sigdecode_der_extended, sigencode_der, sigencode_der_sig_value_a, sigencode_string
 from .util import sigdecode_der, sigdecode_string
 from .curves import curves, SECP112r2, SECP128r1
 from .der import (
@@ -305,7 +305,7 @@ def test_random_der_ecdsa_sig_value_full_r(params):
 
     with pytest.raises(BadSignatureError):
         verifying_key.verify(
-            sig, example_data, sigdecode=sigdecode_der)
+            sig, example_data, sigdecode=sigdecode_der_extended)
 
 
 @settings(**slow_params)
@@ -319,7 +319,7 @@ def test_random_der_ecdsa_sig_value_a(params):
 
     with pytest.raises(BadSignatureError):
         verifying_key.verify(
-            sig, example_data, sigdecode=sigdecode_der)
+            sig, example_data, sigdecode=sigdecode_der_extended)
 
 
 def st_der_integer(*args, **kwargs):  # pragma: no cover

src/ecdsa/util.py

@@ -629,6 +629,47 @@ def sigdecode_der(sig_der, order):
     """
     Decoder for DER format of ECDSA signatures.
 
+    DER format of signature is one that uses the :term:`ASN.1` :term:`DER`
+    rules to encode it as a sequence of two integers::
+
+        Ecdsa-Sig-Value ::= SEQUENCE {
+            r       INTEGER,
+            s       INTEGER
+        }
+
+    It's expected that this function will be used as as the ``sigdecode=``
+    parameter to the :func:`ecdsa.keys.VerifyingKey.verify` method.
+
+    :param sig_der: encoded signature
+    :type sig_der: bytes like object
+    :param order: order of the curve over which the signature was computed
+    :type order: int
+
+    :raises UnexpectedDER: when the encoding of signature is invalid
+
+    :return: tuple with decoded ``r`` and ``s`` values of signature
+    :rtype: tuple of ints
+    """
+    sig_der = normalise_bytes(sig_der)
+    # return der.encode_sequence(der.encode_integer(r), der.encode_integer(s))
+    rs_strings, empty = der.remove_sequence(sig_der)
+    if empty != b"":
+        raise der.UnexpectedDER(
+            "trailing junk after DER sig: %s" % binascii.hexlify(empty)
+        )
+    r, rest = der.remove_integer(rs_strings)
+    s, empty = der.remove_integer(rest)
+    if empty != b"":
+        raise der.UnexpectedDER(
+            "trailing junk after DER numbers: %s" % binascii.hexlify(empty)
+        )
+    return r, s
+
+
+def sigdecode_der_extended(sig_der, order):
+    """
+    Decoder for DER format of ECDSA signatures.
+
     DER format of signature is one that uses the :term:`ASN.1` :term:`DER`
     rules to encode it as one of the choices::
 
@@ -655,7 +696,7 @@ def sigdecode_der(sig_der, order):
     # what signature is encoded depends on the tag presence
     if not der.is_sequence(sig_der):
         return sigdecode_der_full_r(sig_der, order)
-    return sigdecode_der_ecdsa_sig_value(sig_der, order)
+    return sigdecode_der_ecdsa_sig_extended(sig_der, order)
 
 
 def sigdecode_der_full_r(sig_der, order):
@@ -708,7 +749,7 @@ def sigdecode_der_full_r(sig_der, order):
     return r, s
 
 
-def sigdecode_der_ecdsa_sig_value(sig_der, order):
+def sigdecode_der_ecdsa_sig_extended(sig_der, order):
     """
     Decoder for DER format of ECDSA-Sig-Value signatures.