Apply suggestions from code review

Co-authored-by: Jack Grigg <[email protected]>

Author: daira

zcash_test_vectors/zip_0032.py

@@ -50,25 +50,23 @@ def __init__(self, IKM, path, sk, chaincode, full_width=None):
         self.full_width = full_width  # the full-width cryptovalue at this path
 
     @classmethod
-    def master(cls, ContextString, S):
+    def master(cls, ContextString, S, ZipNumber):
         length_ContextString = len(ContextString)
         length_S = len(S)
 
         assert length_ContextString <= 252
         assert 32 <= length_S <= 252
 
         IKM = bytes([length_ContextString]) + ContextString + bytes([length_S]) + S
-        (sk, chaincode) = MKGh(cls.Registered, IKM)
-        return cls(IKM, [], sk, chaincode)
-
-    def child(self, i):
-        (sk_child, c_child) = CKDh(self.Registered, self.sk, self.chaincode, i, 0, b"")
-        return self.__class__(None, self.path + [i], sk_child, c_child)
+        (sk_m, c_m) = MKGh(cls.Registered, IKM)
+        i = hardened(ZipNumber)
+        (sk, chaincode) = CKDh(self.Registered, sk_m, c_m, i, 0, b"")
+        return cls(IKM, [i], sk, chaincode)
 
-    def child_with_tag(self, i, tag):
+    def child(self, i, tag):
         (sk_child, c_child) = CKDh(self.Registered, self.sk, self.chaincode, i, 0, tag)
-        (left, right) = CKDh(self.Registered, self.sk, self.chaincode, i, 1, tag)
-        return self.__class__(None, self.path + [(i, tag)], sk_child, c_child, left + right)
+        (I_L, I_R) = CKDh(self.Registered, self.sk, self.chaincode, i, 1, tag)
+        return self.__class__(None, self.path + [(i, tag)], sk_child, c_child, I_L + I_R)
 
 
 def registered_key_derivation_tvs():