throw error on incorrect bare SigningKey() constructor

ecdsa/keys.py

@@ -14,9 +14,13 @@ class BadDigestError(Exception):
     pass
 
 class VerifyingKey:
+    def __init__(self, _error__please_use_generate=None):
+        if not _error__please_use_generate:
+            raise TypeError("Please use SigningKey.generate() to construct me")
+
     @classmethod
     def from_public_point(klass, point, curve=NIST192p):
-        self = klass()
+        self = klass(_error__please_use_generate=True)
         self.curve = curve
         self.pubkey = ecdsa.Public_key(curve.generator, point)
         self.pubkey.order = curve.order
@@ -103,6 +107,10 @@ def verify_digest(self, signature, digest, sigdecode=sigdecode_string):
         raise BadSignatureError
 
 class SigningKey:
+    def __init__(self, _error__please_use_generate=None):
+        if not _error__please_use_generate:
+            raise TypeError("Please use SigningKey.generate() to construct me")
+
     @classmethod
     def generate(klass, curve=NIST192p, entropy=None):
         secexp = randrange(curve.order, entropy)
@@ -115,7 +123,7 @@ def generate(klass, curve=NIST192p, entropy=None):
 
     @classmethod
     def from_secret_exponent(klass, secexp, curve=NIST192p):
-        self = klass()
+        self = klass(_error__please_use_generate=True)
         self.curve = curve
         self.baselen = curve.baselen
         n = curve.order

ecdsa/test_pyecdsa.py

@@ -45,6 +45,11 @@ def test_basic(self):
         pub2 = VerifyingKey.from_string(pub.to_string())
         self.failUnless(pub2.verify(sig, data))
 
+    def test_bad_usage(self):
+        # sk=SigningKey() is wrong
+        self.failUnlessRaises(TypeError, SigningKey)
+        self.failUnlessRaises(TypeError, VerifyingKey)
+
     def test_lengths(self):
         default = NIST192p
         priv = SigningKey.generate()