Use ticks to hash dates in election descriptions (#192)

Author: rkorsak

src/electionguard/election.py

@@ -9,7 +9,7 @@
 from .hash import CryptoHashable, hash_elems
 from .logs import log_warning
 from .serializable import Serializable
-from .utils import get_optional
+from .utils import get_optional, to_ticks
 
 
 @unique
@@ -567,8 +567,8 @@ def crypto_hash(self) -> ElementModQ:
         return hash_elems(
             self.election_scope_id,
             str(self.type),
-            self.start_date.isoformat(),
-            self.end_date.isoformat(),
+            to_ticks(self.start_date),
+            to_ticks(self.end_date),
             self.name,
             self.contact_information,
             self.geopolitical_units,

tests/test_election.py

@@ -1,4 +1,5 @@
 import unittest
+from datetime import datetime
 
 from electionguard.election import (
     ContestDescriptionWithPlaceholders,
@@ -9,6 +10,7 @@
 )
 import electionguardtest.election_factory as ElectionFactory
 import electionguardtest.ballot_factory as BallotFactory
+from electionguard.serializable import read_json
 
 election_factory = ElectionFactory.ElectionFactory()
 ballot_factory = BallotFactory.BallotFactory()
@@ -46,6 +48,25 @@ def test_election_has_deterministic_hash(self):
         # Assert
         self.assertEqual(subject1.crypto_hash(), subject2.crypto_hash())
 
+    def test_election_hash_is_consistent_regardless_of_format(self):
+
+        # Act
+        subject1 = election_factory.get_simple_election_from_file()
+        subject1.start_date = read_json('"2020-03-01T08:00:00-05:00"', datetime)
+
+        subject2 = election_factory.get_simple_election_from_file()
+        subject2.start_date = read_json('"2020-03-01T13:00:00-00:00"', datetime)
+
+        subject3 = election_factory.get_simple_election_from_file()
+        subject3.start_date = read_json('"2020-03-01T13:00:00.000-00:00"', datetime)
+
+        subjects = [subject1, subject2, subject3]
+
+        # Assert
+        hashes = [subject.crypto_hash() for subject in subjects]
+        for other_hash in hashes[1:]:
+            self.assertEqual(hashes[0], other_hash)
+
     def test_election_from_file_generates_consistent_internal_description_contest_hashes(
         self,
     ):