Adapt to changes to CKDh in ZIP 32.

Signed-off-by: Daira-Emma Hopwood <daira@jacaranda.org>

zcash_test_vectors/zip_0032.py

@@ -26,14 +26,14 @@ def MKGh(Context, IKM):
     I_R = I[32:]
     return (I_L, I_R)
 
-def CKDh(Context, sk_par, c_par, i, tag, full_width_leaf):
+def CKDh(Context, sk_par, c_par, i, lead, tag):
     assert type(Context) == HardenedOnlyContext
     assert 0x80000000 <= i and i <= 0xFFFFFFFF
+    assert type(lead) == int
     assert type(tag) == bytes
-    assert type(full_width_leaf) == bool
 
-    leaf = b"" if tag == b"" and not full_width_leaf else int(full_width_leaf).to_bytes()
-    I = prf_expand(c_par, Context.CKDDomain + sk_par + i2leosp(32, i) + leaf + tag)
+    lead_enc = bytes([] if lead == 0 and tag == b"" else [lead])
+    I = prf_expand(c_par, Context.CKDDomain + sk_par + i2leosp(32, i) + lead_enc + tag)
     I_L = I[:32]
     I_R = I[32:]
     return (I_L, I_R)
@@ -62,12 +62,12 @@ def master(cls, ContextString, S):
         return cls(IKM, [], sk, chaincode)
 
     def child(self, i):
-        (sk_child, c_child) = CKDh(self.Context, self.sk, self.chaincode, i, b"", False)
+        (sk_child, c_child) = CKDh(self.Context, self.sk, self.chaincode, i, 0, b"")
         return self.__class__(None, self.path + [i], sk_child, c_child)
 
     def child_with_tag(self, i, tag):
-        (sk_child, c_child) = CKDh(self.Context, self.sk, self.chaincode, i, tag, False)
-        (left, right) = CKDh(self.Context, self.sk, self.chaincode, i, tag, True)
+        (sk_child, c_child) = CKDh(self.Context, self.sk, self.chaincode, i, 0, tag)
+        (left, right) = CKDh(self.Context, self.sk, self.chaincode, i, 1, tag)
         return self.__class__(None, self.path + [(i, tag)], sk_child, c_child, left + right)