added tests for ciphertext format

kyber/decrypt.py

@@ -11,6 +11,8 @@ def __init__(self, private_key, ciphertext) -> None:
         self._c = ciphertext
         if len(self._sk) != 32*12*k:
             raise ValueError()
+        if len(self._c) != du*k*n//8 + dv*n//8:
+            raise ValueError()
 
     def decrypt(self) -> bytes:
         """

tests/test_decryption.py

@@ -1,13 +1,29 @@
 import unittest
 from random import seed, randbytes
 from kyber.decrypt import Decrypt
-from kyber.constants import k
+from kyber.constants import k, n, du, dv
 
 class TestDecryption(unittest.TestCase):
-    def test_decryption_raises_with_invalid_input(self):
-        # this private key is one byte too long
+    def setUp(self):
         seed(42)
+
+    def test_decryption_outputs_valid_shared_secret(self):
+        private_key = randbytes(32*12*k)
+        ciphertext = randbytes(du*k*n//8 + dv*n//8)
+        shared_secret = Decrypt(private_key, ciphertext).decrypt()
+        self.assertEqual(type(shared_secret), bytes)
+        self.assertEqual(len(shared_secret), 32)
+
+    def test_decryption_raises_with_invalid_private_key(self):
+        # this private key is one byte too long
         invalid_private_key = randbytes(32*12*k + 1)
-        ciphertext_placeholder = ()
+        valid_ciphertext = randbytes(du*k*n//8 + dv*n//8)
+        with self.assertRaises(ValueError):
+            Decrypt(invalid_private_key, valid_ciphertext)
+
+    def test_decryption_raises_with_invalid_ciphertext(self):
+        # this ciphertext is one byte too short
+        valid_private_key = randbytes(32*12*k)
+        invalid_ciphertext = randbytes(du*k*n//8 + dv*n//8 - 1)
         with self.assertRaises(ValueError):
-            Decrypt(invalid_private_key, ciphertext_placeholder)
+            Decrypt(valid_private_key, invalid_ciphertext)

tests/test_encryption.py

@@ -1,7 +1,7 @@
 import unittest
 from random import seed, randbytes
 from kyber.encrypt import Encrypt
-from kyber.constants import k, n
+from kyber.constants import k, n, du, dv
 
 class TestEncryption(unittest.TestCase):
     def test_encryption_raises_with_invalid_input(self):
@@ -15,3 +15,9 @@ def test_encryption_generates_valid_shared_secret(self):
         seed(42)
         encrypter = Encrypt(randbytes(12 * k * n//8 + 32))
         self.assertEqual(len(encrypter.secret), 32)
+
+    def test_encryption_outputs_valid_ciphertext(self):
+        seed(42)
+        ciphertext = Encrypt(randbytes(12 * k * n//8 + 32)).encrypt()
+        self.assertEqual(type(ciphertext), bytes)
+        self.assertEqual(len(ciphertext), du*k*n//8 + dv*n//8)