Add a tool for matching the node key in the announcement

And use it in the recently added test

src/allmydata/test/matchers.py

@@ -2,7 +2,10 @@
 Testtools-style matchers useful to the Tahoe-LAFS test suite.
 """
 
+import attr
+
 from testtools.matchers import (
+    Mismatch,
     AfterPreprocessing,
     MatchesStructure,
     MatchesDict,
@@ -17,9 +20,37 @@ from foolscap.furl import (
 from allmydata.util import (
     base32,
 )
+from allmydata.node import (
+    read_config,
+)
+from allmydata.crypto import (
+    ed25519,
+    error,
+)
+
+@attr.s
+class MatchesNodePublicKey(object):
+    """
+    Match an object representing the node's private key.
+
+    To verify, the private key is loaded from the node's private config
+    directory at the time the match is checked.
+    """
+    basedir = attr.ib()
+
+    def match(self, other):
+        config = read_config(self.basedir, u"tub.port")
+        privkey_bytes = config.get_private_config("node.privkey")
+        private_key = ed25519.signing_keypair_from_string(privkey_bytes)[0]
+        signature = ed25519.sign_data(private_key, b"")
+        other_public_key = ed25519.verifying_key_from_signing_key(other)
+        try:
+            ed25519.verify_signature(other_public_key, signature, b"")
+        except error.BadSignature:
+            return Mismatch("The signature did not verify.")
 
 
-def matches_anonymous_storage_announcement():
+def matches_anonymous_storage_announcement(basedir):
     """
     Match an anonymous storage announcement.
     """
@@ -30,8 +61,7 @@ def matches_anonymous_storage_announcement():
             "anonymous-storage-FURL": matches_furl(),
             "permutation-seed-base32": matches_base32(),
         }),
-        # Not sure what kind of assertion to make against the key
-        signing_key=Always(),
+        signing_key=MatchesNodePublicKey(basedir),
     )
 
 

src/allmydata/test/test_client.py

@@ -1122,7 +1122,7 @@ introducer.furl = pb://abcde@nowhere/fake
                 # Match the following list (of one element) ...
                 MatchesListwise([
                     # The only element in the list ...
-                    matches_anonymous_storage_announcement(),
+                    matches_anonymous_storage_announcement(self.basedir),
                 ]),
             )),
         )