Initial commit

cell.py

@@ -0,0 +1,113 @@
+import nacl
+
+from msg import RelayNetMsg
+
+class RelayCell(RelayNetMsg):
+    """All cells (which are sent inside a CircuitCellMsg, and so do not
+    need their own circuitid) should be a subclass of this class."""
+
+
+class StringCell(RelayCell):
+    """Send an arbitrary string as a cell."""
+    def __init__(self, str):
+        self.data = str
+
+    def __str__(self):
+        return self.data.__str__()
+
+
+class CloseCell(RelayCell):
+    """Close the circuit this cell was sent on.  It should be sent
+    _unencrypted_ (not within an EncryptedCell), and relays that receive
+    one should forward it along the adjacent circuit, then close both
+    the circuit it was received on and the adjacent one."""
+
+
+class VanillaCreatedCircuitCell(RelayCell):
+    """The message for responding to circuit creation in Vanilla Onion
+    Routing."""
+
+    def __init__(self, ntor_reply):
+        self.ntor_reply = ntor_reply
+
+
+class VanillaExtendCircuitCell(RelayCell):
+    """The message for requesting circuit extension in Vanilla Onion
+    Routing."""
+
+    def __init__(self, hopaddr, ntor_request):
+        self.hopaddr = hopaddr
+        self.ntor_request = ntor_request
+
+
+class VanillaExtendedCircuitCell(RelayCell):
+    """The message for responding to circuit extension in Vanilla Onion
+    Routing."""
+
+    def __init__(self, ntor_reply):
+        self.ntor_reply = ntor_reply
+
+
+class TelescopingCreatedCircuitCell(RelayCell):
+    """The message for responding to circuit creation in Telescoping Walking
+    Onions."""
+
+    def __init__(self, ntor_reply):
+        self.ntor_reply = ntor_reply
+
+
+class TelescopingExtendCircuitCell(RelayCell):
+    """The message for requesting circuit extension in Telescoping Walking
+    Onions."""
+
+    def __init__(self, idx, ntor_request):
+        self.idx = idx
+        self.ntor_request = ntor_request
+
+
+class TelescopingExtendedCircuitCell(RelayCell):
+    """The message for responding to circuit extension in Telescoping Walking
+    Onions."""
+
+    def __init__(self, ntor_reply, snip):
+        self.ntor_reply = ntor_reply
+        self.snip = snip
+
+class SinglePassCreatedCircuitCell(RelayCell):
+    """The message for responding to circuit creation in Single-Pass Walking
+    Onions."""
+
+    def __init__(self, ntor_reply, encrypted_cell):
+        self.ntor_reply = ntor_reply
+        # The above field is sent in plaintext; the below is an
+        # SinglePassCreatedEnc, or None if this is the last layer
+        self.enc = encrypted_cell
+
+
+class EncryptedCell(RelayCell):
+    """Send a message encrypted with a symmetric key.  In this
+    implementation, the encryption is not really done.  A hash of the
+    key is stored with the message so that it can be checked at
+    decryption time."""
+
+    def __init__(self, key, msg):
+        self.keyhash = nacl.hash.sha256(key)
+        self.plaintext = msg
+
+    def decrypt(self, key):
+        keyhash = nacl.hash.sha256(key)
+        if keyhash != self.keyhash:
+            raise ValueError("EncryptedCell key mismatch")
+        return self.plaintext
+
+    def size(self):
+        # Current Tor actually has no overhead for encryption
+        return self.plaintext.size()
+
+
+class SinglePassCreatedEnc(EncryptedCell):
+    """The nested encrypted informaion inside a
+    SinglePassCreatedCircuitCell.  nextlayer is itself a
+    SinglePassCreatedCircuitCell."""
+    def __init__(self, key, snip, vrf_output, nextlayer):
+        super().__init__(key, (snip, vrf_output, nextlayer))