Add VerifiedKeyFrag.from_verified_bytes() for the purposes of Nucypher's datastore

docs/source/api.rst

@@ -40,6 +40,7 @@ Intermediate objects
     :show-inheritance:
 
 .. autoclass:: VerifiedKeyFrag()
+    :members:
     :special-members: __eq__, __hash__
 
 .. autoclass:: CapsuleFrag()

tests/test_key_frag.py

@@ -1,7 +1,7 @@
 import pytest
 
 from umbral import KeyFrag, PublicKey, Signer, VerificationError
-from umbral.key_frag import KeyFragID, KeyFragBase
+from umbral.key_frag import KeyFragID, KeyFragBase, VerifiedKeyFrag
 from umbral.curve_scalar import CurveScalar
 
 
@@ -124,3 +124,9 @@ def test_kfrag_str(kfrags):
     s = str(KeyFrag.from_bytes(bytes(kfrags[0])))
     assert "VerifiedKeyFrag" not in s
     assert "KeyFrag" in s
+
+
+def test_from_verified_bytes(kfrags):
+    kfrag_bytes = bytes(kfrags[0])
+    verified_kfrag = VerifiedKeyFrag.from_verified_bytes(kfrag_bytes)
+    assert verified_kfrag == kfrags[0]

umbral/key_frag.py

@@ -253,6 +253,18 @@ class VerifiedKeyFrag:
     def __bytes__(self):
         return bytes(self.kfrag)
 
+    @classmethod
+    def from_verified_bytes(cls, data) -> 'VerifiedKeyFrag':
+        """
+        Restores a verified keyfrag directly from serialized bytes,
+        skipping :py:meth:`KeyFrag.verify` call.
+
+        Intended for internal storage;
+        make sure that the bytes come from a trusted source.
+        """
+        kfrag = KeyFrag.from_bytes(data)
+        return cls(kfrag)
+
     def __eq__(self, other):
         return self.kfrag == other.kfrag