class MyVerifyingKey, with constructor to submit to python-ecdsa

lib/bitcoin.py

@@ -406,6 +406,34 @@ def ser_to_point(Aser):
 
 
 
+class MyVerifyingKey(ecdsa.VerifyingKey):
+    @classmethod
+    def from_signature(klass, sig, recid, h, curve):
+        """ See http://www.secg.org/download/aid-780/sec1-v2.pdf, chapter 4.1.6 """
+        from ecdsa import util, numbertheory
+        import msqr
+        curveFp = curve.curve
+        G = curve.generator
+        order = G.order()
+        # extract r,s from signature
+        r, s = util.sigdecode_string(sig, order)
+        # 1.1
+        x = r + (recid/2) * order
+        # 1.3
+        alpha = ( x * x * x  + curveFp.a() * x + curveFp.b() ) % curveFp.p()
+        beta = msqr.modular_sqrt(alpha, curveFp.p())
+        y = beta if (beta - recid) % 2 == 0 else curveFp.p() - beta
+        # 1.4 the constructor checks that nR is at infinity
+        R = Point(curveFp, x, y, order)
+        # 1.5 compute e from message:
+        e = string_to_number(h)
+        minus_e = -e % order
+        # 1.6 compute Q = r^-1 (sR - eG)
+        inv_r = numbertheory.inverse_mod(r,order)
+        Q = inv_r * ( s * R + minus_e * G )
+        return klass.from_public_point( Q, curve )
+
+
 class EC_KEY(object):
     def __init__( self, k ):
         secret = string_to_number(k)
@@ -434,16 +462,9 @@ class EC_KEY(object):
 
     @classmethod
     def verify_message(self, address, signature, message):
-        """ See http://www.secg.org/download/aid-780/sec1-v2.pdf for the math """
-        from ecdsa import numbertheory, util
-        import msqr
-        curve = curve_secp256k1
-        G = generator_secp256k1
-        order = G.order()
-        # extract r,s from signature
         sig = base64.b64decode(signature)
         if len(sig) != 65: raise Exception("Wrong encoding")
-        r,s = util.sigdecode_string(sig[1:], order)
+
         nV = ord(sig[0])
         if nV < 27 or nV >= 35:
             raise Exception("Bad encoding")
@@ -454,24 +475,12 @@ class EC_KEY(object):
             compressed = False
 
         recid = nV - 27
-        # 1.1
-        x = r + (recid/2) * order
-        # 1.3
-        alpha = ( x * x * x  + curve.a() * x + curve.b() ) % curve.p()
-        beta = msqr.modular_sqrt(alpha, curve.p())
-        y = beta if (beta - recid) % 2 == 0 else curve.p() - beta
-        # 1.4 the constructor checks that nR is at infinity
-        R = Point(curve, x, y, order)
-        # 1.5 compute e from message:
         h = Hash( msg_magic(message) )
-        e = string_to_number(h)
-        minus_e = -e % order
-        # 1.6 compute Q = r^-1 (sR - eG)
-        inv_r = numbertheory.inverse_mod(r,order)
-        Q = inv_r * ( s * R + minus_e * G )
-        public_key = ecdsa.VerifyingKey.from_public_point( Q, curve = SECP256k1 )
-        # check that Q is the public key
+        public_key = MyVerifyingKey.from_signature( sig[1:], recid, h, curve = SECP256k1 )
+
+        # check public key
         public_key.verify_digest( sig[1:], h, sigdecode = ecdsa.util.sigdecode_string)
+
         # check that we get the original signing address
         addr = public_key_to_bc_address( point_to_ser(public_key.pubkey.point, compressed) )
         if address != addr: