Facility for clearing CFrags.

tests/unit/test_capsule_operations.py

@@ -121,3 +121,15 @@ def test_capsule_length(prepared_capsule, kfrags):
         assert len(capsule) == counter
         cfrag = pre.reencrypt(kfrag, capsule)
         capsule.attach_cfrag(cfrag)
+
+
+def test_capsule_clear(prepared_capsule, kfrags):
+    capsule = prepared_capsule
+
+    for counter, kfrag in enumerate(kfrags):
+        assert len(capsule) == counter
+        cfrag = pre.reencrypt(kfrag, capsule)
+        capsule.attach_cfrag(cfrag)
+
+    capsule.clear_cfrags()
+    assert len(capsule) == 0

umbral/pre.py

@@ -176,6 +176,9 @@ class Capsule:
             error_msg = "CFrag is not correct and cannot be attached to the Capsule"
             raise UmbralCorrectnessError(error_msg, [cfrag])
 
+    def clear_cfrags(self):
+        self._attached_cfrags = set()
+
     def first_cfrag(self):
         try:
             return list(self._attached_cfrags)[0]