add support for finding Curves by name

Author: tomato42

src/ecdsa/curves.py

@@ -23,6 +23,7 @@
     "NIST521p",
     "curves",
     "find_curve",
+    "curve_by_name",
     "SECP256k1",
     "BRAINPOOLP160r1",
     "BRAINPOOLP192r1",
@@ -476,3 +477,27 @@ def find_curve(oid_curve):
         "I don't know about the curve with oid %s."
         "I only know about these: %s" % (oid_curve, [c.name for c in curves])
     )
+
+
+def curve_by_name(name):
+    """Select a curve based on its name.
+
+    Returns a :py:class:`~ecdsa.curves.Curve` object with a ``name`` name.
+    Note that ``name`` is case-sensitve.
+
+    :param str name: Name of the curve to return, like ``NIST256p`` or
+        ``prime256v1``
+
+    :raises UnknownCurveError: When the name doesn't match any of the supported
+        curves
+
+    :rtype: ~ecdsa.curves.Curve
+    """
+    for c in curves:
+        if name == c.name or (c.openssl_name and name == c.openssl_name):
+            return c
+    raise UnknownCurveError(
+        "Curve with name {0!r} unknown, only curves supported: {1}".format(
+            name, [c.name for c in curves]
+        )
+    )

src/ecdsa/test_curves.py

@@ -5,7 +5,14 @@
 
 import base64
 import pytest
-from .curves import Curve, NIST256p, curves, UnknownCurveError, PRIME_FIELD_OID
+from .curves import (
+    Curve,
+    NIST256p,
+    curves,
+    UnknownCurveError,
+    PRIME_FIELD_OID,
+    curve_by_name,
+)
 from .ellipticcurve import CurveFp, PointJacobi, CurveEdTw
 from . import der
 from .util import number_to_string
@@ -288,6 +295,36 @@ def test_decode_malformed_garbage_after_prime(self):
         self.assertIn("Prime-p element", str(e.exception))
 
 
+class TestCurveSearching(unittest.TestCase):
+    def test_correct_name(self):
+        c = curve_by_name("NIST256p")
+        self.assertIs(c, NIST256p)
+
+    def test_openssl_name(self):
+        c = curve_by_name("prime256v1")
+        self.assertIs(c, NIST256p)
+
+    def test_unknown_curve(self):
+        with self.assertRaises(UnknownCurveError) as e:
+            curve_by_name("foo bar")
+
+        self.assertIn(
+            "name 'foo bar' unknown, only curves supported: "
+            "['NIST192p', 'NIST224p'",
+            str(e.exception),
+        )
+
+    def test_with_None_as_parameter(self):
+        with self.assertRaises(UnknownCurveError) as e:
+            curve_by_name(None)
+
+        self.assertIn(
+            "name None unknown, only curves supported: "
+            "['NIST192p', 'NIST224p'",
+            str(e.exception),
+        )
+
+
 @pytest.mark.parametrize("curve", curves, ids=[i.name for i in curves])
 def test_curve_params_encode_decode_named(curve):
     ret = Curve.from_der(curve.to_der("named_curve"))