Replace `dem.ErrorInvalidTag` and `Capsule.NotValid` with `GenericError`.

docs/examples/umbral_simple_api.py

@@ -1,8 +1,7 @@
 import random
 from umbral import (
-    SecretKey, PublicKey,
+    SecretKey, PublicKey, GenericError,
     encrypt, generate_kfrags, reencrypt, decrypt_original, decrypt_reencrypted)
-from umbral.dem import ErrorInvalidTag
 
 # Generate an Umbral key pair
 # ---------------------------
@@ -46,7 +45,7 @@ bob_capsule = capsule
 # Attempt Bob's decryption (fail)
 try:
     fail_decrypted_data = decrypt_original(bobs_secret_key, bob_capsule, ciphertext)
-except ErrorInvalidTag:
+except GenericError:
     print("Decryption failed! Bob doesn't has access granted yet.")
 
 # Alice grants access to Bob by generating kfrags

docs/notebooks/pyUmbral Simple API.ipynb

@@ -140,13 +140,13 @@
     }
    ],
    "source": [
-    "from umbral.dem import ErrorInvalidTag\n",
+    "from umbral import GenericError\n",
     "\n",
     "try:\n",
     "    fail_decrypted_data = decrypt_original(sk=bobs_private_key,\n",
     "                                           capsule=capsule,\n",
     "                                           ciphertext=ciphertext)\n",
-    "except ErrorInvalidTag:\n",
+    "except GenericError:\n",
     "    print(\"Decryption failed! Bob doesn't has access granted yet.\")\n"
    ]
   },

docs/source/api.rst

@@ -52,6 +52,9 @@ Encryption, re-encryption and decryption
 Utilities
 ---------
 
+.. autoclass:: umbral.GenericError
+    :show-inheritance:
+
 .. autoclass:: umbral.serializable.Serializable
     :members: from_bytes
     :special-members: __bytes__

docs/source/using_pyumbral.rst

@@ -134,7 +134,7 @@ or re-encrypted for him by Ursula, he will not be able to open it.
     ...                         ciphertext=ciphertext)
     Traceback (most recent call last):
         ...
-    umbral.dem.ErrorInvalidTag
+    umbral.GenericError
 
 
 Ursulas perform re-encryption

tests/test_capsule.py

@@ -4,6 +4,7 @@ from umbral import (
     Capsule,
     SecretKey,
     PublicKey,
+    GenericError,
     encrypt,
     decrypt_original,
     reencrypt,
@@ -27,7 +28,7 @@ def test_capsule_serialization(alices_keys):
     capsule.point_e = CurvePoint.random()
     capsule_bytes = bytes(capsule)
 
-    with pytest.raises(Capsule.NotValid):
+    with pytest.raises(GenericError):
         Capsule.from_bytes(capsule_bytes)
 
 
@@ -84,7 +85,7 @@ def test_open_reencrypted(alices_keys, bobs_keys):
         capsule.open_reencrypted(receiving_sk, delegating_pk, [])
 
     # Not enough cfrags
-    with pytest.raises(ValueError, match="Internal validation failed"):
+    with pytest.raises(GenericError, match="Internal validation failed"):
         capsule.open_reencrypted(receiving_sk, delegating_pk, cfrags[:threshold-1])
 
     # Repeating cfrags

tests/test_dem.py

@@ -1,7 +1,8 @@
 import pytest
 import os
 
-from umbral.dem import DEM, ErrorInvalidTag
+from umbral import GenericError
+from umbral.dem import DEM
 
 
 def test_encrypt_decrypt():
@@ -47,7 +48,7 @@ def test_malformed_ciphertext():
         dem.decrypt(ciphertext[:DEM.NONCE_SIZE + DEM.TAG_SIZE - 1])
 
     # Too long
-    with pytest.raises(ErrorInvalidTag):
+    with pytest.raises(GenericError):
         dem.decrypt(ciphertext + b'abcd')
 
 
@@ -76,5 +77,5 @@ def test_encrypt_decrypt_associated_data():
     assert cleartext1 == plaintext
 
     # Attempt decryption with invalid associated data
-    with pytest.raises(ErrorInvalidTag):
+    with pytest.raises(GenericError):
         cleartext2 = dem.decrypt(ciphertext0, authenticated_data=b'wrong data')

tests/test_pre.py

@@ -3,13 +3,13 @@ import pytest
 from umbral import (
     SecretKey,
     PublicKey,
+    GenericError,
     encrypt,
     generate_kfrags,
     decrypt_original,
     reencrypt,
     decrypt_reencrypted,
     )
-from umbral.dem import ErrorInvalidTag
 
 
 def test_public_key_encryption(alices_keys):
@@ -22,7 +22,7 @@ def test_public_key_encryption(alices_keys):
 
     # Wrong secret key
     sk = SecretKey.random()
-    with pytest.raises(ErrorInvalidTag):
+    with pytest.raises(GenericError):
         decrypt_original(sk, capsule, ciphertext)
 
 

umbral/__init__.py

@@ -4,6 +4,7 @@ from .__about__ import (
 
 from .capsule import Capsule
 from .capsule_frag import CapsuleFrag
+from .errors import GenericError
 from .key_frag import KeyFrag, generate_kfrags
 from .keys import SecretKey, PublicKey, SecretKeyFactory
 from .pre import encrypt, decrypt_original, decrypt_reencrypted, reencrypt
@@ -23,6 +24,7 @@ __all__ = [
     "Capsule",
     "KeyFrag",
     "CapsuleFrag",
+    "GenericError",
     "encrypt",
     "decrypt_original",
     "generate_kfrags",

umbral/capsule.py

@@ -2,6 +2,7 @@ from typing import TYPE_CHECKING, Tuple, Sequence
 
 from .curve_point import CurvePoint
 from .curve_scalar import CurveScalar
+from .errors import GenericError
 from .hashing import hash_capsule_points, hash_to_polynomial_arg, hash_to_shared_secret
 from .keys import PublicKey, SecretKey
 from .params import PARAMETERS
@@ -24,11 +25,6 @@ class Capsule(Serializable):
     Encapsulated symmetric key.
     """
 
-    class NotValid(ValueError):
-        """
-        raised if the capsule does not pass verification.
-        """
-
     def __init__(self, point_e: CurvePoint, point_v: CurvePoint, signature: CurveScalar):
         self.point_e = point_e
         self.point_v = point_v
@@ -40,7 +36,7 @@ class Capsule(Serializable):
 
         capsule = cls(e, v, sig)
         if not capsule._verify():
-            raise cls.NotValid("Capsule verification failed.")
+            raise GenericError("Capsule self-verification failed. Serialized data may be damaged.")
 
         return capsule, data
 
@@ -111,7 +107,7 @@ class Capsule(Serializable):
         # TODO: check for d == 0? Or just let if fail?
         inv_d = d.invert()
         if orig_pub_key * (s * inv_d) != (e_prime * h) + v_prime:
-            raise ValueError("Internal validation failed")
+            raise GenericError("Internal validation failed")
 
         return (e_prime + v_prime) * d
 

umbral/dem.py

@@ -14,6 +14,7 @@ from nacl.bindings.crypto_aead import (
     )
 
 from . import openssl
+from .errors import GenericError
 
 
 def kdf(data: bytes,
@@ -30,10 +31,6 @@ def kdf(data: bytes,
     return hkdf.derive(data)
 
 
-class ErrorInvalidTag(Exception):
-    pass
-
-
 class DEM:
 
     KEY_SIZE = XCHACHA_KEY_SIZE
@@ -67,4 +64,6 @@ class DEM:
         try:
             return xchacha_decrypt(ciphertext, authenticated_data, nonce, self._key)
         except nacl.exceptions.CryptoError:
-            raise ErrorInvalidTag
+            raise GenericError("Decryption of ciphertext failed: "
+                               "either someone tampered with the ciphertext or "
+                               "you are using an incorrect decryption key.")

umbral/errors.py

@@ -0,0 +1,5 @@
+class GenericError(Exception):
+    """
+    An interal Umbral error, see the message for details.
+    """
+    pass