Add verify_ballot method and edit accompanying test (#457)

* add verify_ballot method and edit accompanying test

* change InternalManifest with Manifest in parameter

* rename election to manifest in test_verify_ballot

Co-authored-by: Keith Fung <keithrfung@users.noreply.github.com>

Author: PradyumnaKrishna

src/electionguard_verify/verify.py

@@ -4,6 +4,10 @@
 from electionguard.ballot import (
     CiphertextBallot,
 )
+from electionguard.election import CiphertextElectionContext
+from electionguard.manifest import (
+    Manifest,
+)
 
 
 @dataclass
@@ -17,13 +21,23 @@ class Verification:
     message: Optional[str]
 
 
-def verify_ballot(ballot: CiphertextBallot) -> Verification:
+def verify_ballot(
+    ballot: CiphertextBallot,
+    manifest: Manifest,
+    context: CiphertextElectionContext,
+) -> Verification:
     """
     Method to verify the validity of a ballot
-
-    TEMPORARY method that always returns True!!!
     """
 
-    print(f"Verifying ballot {ballot.object_id}")
+    if not ballot.is_valid_encryption(
+        manifest.crypto_hash(),
+        context.elgamal_public_key,
+        context.crypto_extended_base_hash,
+    ):
+        return Verification(
+            False,
+            message=f"verify_ballot: mismatching ballot encryption {ballot.object_id}",
+        )
 
     return Verification(True, message=None)

tests/property/test_verify.py

@@ -30,9 +30,9 @@ class TestVerify(BaseTestCase):
     @given(elgamal_keypairs())
     def test_verify_ballot(self, keypair: ElGamalKeyPair):
         # Arrange
-        election = election_factory.get_simple_manifest_from_file()
+        manifest = election_factory.get_simple_manifest_from_file()
         internal_manifest, context = election_factory.get_fake_ciphertext_election(
-            election, keypair.public_key
+            manifest, keypair.public_key
         )
 
         data = ballot_factory.get_simple_ballot_from_file()
@@ -43,8 +43,8 @@ def test_verify_ballot(self, keypair: ElGamalKeyPair):
         self.assertIsNotNone(encrypted_ballot)
 
         # Act
-        verification = verify_ballot(encrypted_ballot)
+        verification = verify_ballot(encrypted_ballot, manifest, context)
 
         # Assert
         self.assertIsNotNone(verification)
-        self.assertTrue(verification)
+        self.assertTrue(verification.verified)