casey feedback

ch03.asciidoc

@@ -679,7 +679,7 @@ One subtle thing that we haven't talked about is that we have to incorporate the
 
 In signature/verification parlance, this is called the _signature hash_. This generally is the hash of the message that both parties agree to that reveal the intent of the shooter. We denote this with the letter `z`. This is incorporated into our uG+vP calculation this way:
 
-u = r/s, v = z/s
+u = z/s, v = r/s
 
 Since r is used in the calculation of u, we now have the tip of the arrow forged. We also have the intent of the shooter incorporated into v, so both the reason for shooting and the target that is being aimed at are now a part of the equation.
 
@@ -691,19 +691,19 @@ uG+veG=kG
 
 u+ve=k
 
-r/s+ze/s=k
+z/s+re/s=k
 
-(r+ze)/s=k
+(z+re)/s=k
 
-s=(r+ze)/k
+s=(z+re)/k
 
 This is indeed the basis of the signature algorithm and the two numbers actually communicated as part of the signature are r and s.
 
 Verification is simple:
 
 uG+vP where u,v≠0
 
-uG+vP=(r/s)G+(ze/s)G=((r+ze)/s)G=((r+ze)/((r+ze)/k))G=kG=(r,y)
+uG+vP=(z/s)G+(re/s)G=((z+re)/s)G=((z+re)/((z+re)/k))G=kG=(r,y)
 
 .Why We Don't Reveal `k`
 ****

code-ch03/ecc.py

@@ -136,7 +136,6 @@ def test_div(self):
 
 
 class Point:
-    zero = 0
 
     def __init__(self, x, y, a, b):
         self.a = a
@@ -166,7 +165,7 @@ def __repr__(self):
         if self.x is None:
             return 'Point(infinity)'
         else:
-            return 'Point({},{})_{}'.format(self.x.num, self.y.num, self.x.prime)
+            return 'Point({},{})_{}_{}'.format(self.x, self.y, self.a, self.b)
 
     def __add__(self, other):
         if self.a != other.a or self.b != other.b:
@@ -195,19 +194,20 @@ def __add__(self, other):
             return self.__class__(x, y, self.a, self.b)
 
         # Case 3: self.x == other.x, self.y == other.y
-        else:
-            # Formula (x3,y3)=(x1,y1)+(x1,y1)
-            # s=(3*x1**2+a)/(2*y1)
-            s = (3 * self.x**2 + self.a) / (2 * self.y)
-            # x3=s**2-2*x1
-            x = s**2 - 2 * self.x
-            # y3=s*(x1-x3)-y1
-            y = s * (self.x - x) - self.y
-            return self.__class__(x, y, self.a, self.b)
-
-        # Case 4: if we are tangent to the vertical line
-        if self == other and self.y == self.zero:
-            return self.__class__(None, None, self.a, self.b)
+        if self == other:
+            # Case 4: if we are tangent to the vertical line
+            # note instead of figuring out what 0 is for each type, we just use 0 * self.x
+            if self.y == 0 * self.x:
+                return self.__class__(None, None, self.a, self.b)
+            else:
+                # Formula (x3,y3)=(x1,y1)+(x1,y1)
+                # s=(3*x1**2+a)/(2*y1)
+                s = (3 * self.x**2 + self.a) / (2 * self.y)
+                # x3=s**2-2*x1
+                x = s**2 - 2 * self.x
+                # y3=s*(x1-x3)-y1
+                y = s * (self.x - x) - self.y
+                return self.__class__(x, y, self.a, self.b)
 
     def __rmul__(self, coefficient):
         coef = coefficient
@@ -354,7 +354,6 @@ def __repr__(self):
 
 
 class S256Point(Point):
-
     zero = S256Field(0)
 
     def __init__(self, x, y, a=None, b=None):

code-ch03/helper.py

@@ -1,8 +1,9 @@
-from unittest import TestSuite, TextTestRunner
+from unittest import SkipTest, TestSuite, TextTestRunner
 
 import hashlib
 
 
+@SkipTest
 def run_test(test):
     suite = TestSuite()
     suite.addTest(test)

code-ch05/ecc.py

@@ -570,22 +570,22 @@ def parse(cls, signature_bin):
         s = BytesIO(signature_bin)
         compound = s.read(1)[0]
         if compound != 0x30:
-            raise RuntimeError("Bad Signature")
+            raise IOError("Bad Signature")
         length = s.read(1)[0]
         if length + 2 != len(signature_bin):
-            raise RuntimeError("Bad Signature Length")
+            raise IOError("Bad Signature Length")
         marker = s.read(1)[0]
         if marker != 0x02:
-            raise RuntimeError("Bad Signature")
+            raise IOError("Bad Signature")
         rlength = s.read(1)[0]
         r = int(s.read(rlength).hex(), 16)
         marker = s.read(1)[0]
         if marker != 0x02:
-            raise RuntimeError("Bad Signature")
+            raise IOError("Bad Signature")
         slength = s.read(1)[0]
         s = int(s.read(slength).hex(), 16)
         if len(signature_bin) != 6 + rlength + slength:
-            raise RuntimeError("Signature too long")
+            raise IOError("Signature too long")
         return cls(r, s)