Merge branch 'only-symmetric'

magic-wormhole now only uses the "SPAKE2_Symmetric" protocol, which does
not require the two participants to decide ahead of time which one is
which.

Previously, the blocking form used an asymmetric protocol, and the
non-blocking/Twisted form used a symmetric protocol (however it used an
earlier+slower version from SPAKE2-0.2.0, which is not compatible with
the current SPAKE2-0.3.0 one).

This breaks compatibility for the built-in "wormhole" script: a sender
using 0.3.0 will get errors when talking to a recipient running this
version or newer (including the upcoming 0.4.0 release).

README.md

@@ -113,14 +113,11 @@ All four commands accept:
 ## Library
 
 The `wormhole` module makes it possible for other applications to use these
-code-protected channels. This includes blocking/synchronous support (for an
+code-protected channels. This includes blocking/synchronous support and
-asymmetric pair of "initiator" and "receiver" endpoints), and async/Twisted
+async/Twisted support, both for a symmetric scheme. The main module is named
-support (for a symmetric scheme). The main module is named
 `wormhole.blocking.transcribe`, to reflect that it is for
 synchronous/blocking code, and uses a PAKE mode whereby one user transcribes
-their code to the other. (internal names may change in the future). The
+their code to the other. (internal names may change in the future).
-synchronous support uses distinctive sides: one `Initiator`, and one
-`Receiver`.
 
 The file-transfer tools use a second module named
 `wormhole.blocking.transit`, which provides an encrypted record-pipe. It

docs/api.md

@@ -12,26 +12,48 @@ server" that relays information from one machine to the other.
 
 ## Modes
 
-This library will eventually offer multiple modes.
+This library will eventually offer multiple modes. For now, only "transcribe
+mode" is available.
 
-The first mode provided is "transcribe" mode. In this mode, one machine goes
+Transcribe mode has two variants. In the "machine-generated" variant, the
-first, and is called the "initiator". The initiator contacts the rendezvous
+"initiator" machine creates the invitation code, displays it to the first
-server and allocates a "channel ID", which is a small integer. The initiator
+user, they convey it (somehow) to the second user, who transcribes it into
-then displays the "invitation code", which is the channel-ID plus a few
+the second ("receiver") machine. In the "human-generated" variant, the two
-secret words. The user copies the invitation code to the second machine,
+humans come up with the code (possibly without computers), then later
-called the "receiver". The receiver connects to the rendezvous server, and
+transcribe it into both machines.
-uses the invitation code to contact the initiator. They agree upon an
+
-encryption key, and exchange a small encrypted+authenticated data message.
+When the initator machine generates the invitation code, the initiator
+contacts the rendezvous server and allocates a "channel ID", which is a small
+integer. The initiator then displays the invitation code, which is the
+channel-ID plus a few secret words. The user copies the code to the second
+machine. The receiver machine connects to the rendezvous server, and uses the
+invitation code to contact the initiator. They agree upon an encryption key,
+and exchange a small encrypted+authenticated data message.
+
+When the humans create an invitation code out-of-band, they are responsible
+for choosing an unused channel-ID (simply picking a random 3-or-more digit
+number is probably enough), and some random words. The invitation code uses
+the same format in either variant: channel-ID, a hyphen, and an arbitrary
+string.
+
+The two machines participating in the wormhole setup are not distinguished:
+it doesn't matter which one goes first, and both use the same Wormhole class.
+In the first variant, one side calls `get_code()` while the other calls
+`set_code()`. In the second variant, both sides call `set_code()`. Note that
+this is not true for the "Transit" protocol used for bulk data-transfer: the
+Transit class currently distinguishes "Sender" from "Receiver", so the
+programs on each side must have some way to decide (ahead of time) which is
+which.
 
 ## Examples
 
 The synchronous+blocking flow looks like this:
 
 ```python
-from wormhole.transcribe import Initiator
+from wormhole.transcribe import Wormhole
 from wormhole.public_relay import RENDEZVOUS_RELAY
 mydata = b"initiator's data"
-i = Initiator("appid", RENDEZVOUS_RELAY)
+i = Wormhole("appid", RENDEZVOUS_RELAY)
 code = i.get_code()
 print("Invitation Code: %s" % code)
 theirdata = i.get_data(mydata)
@@ -40,11 +62,11 @@ print("Their data: %s" % theirdata.decode("ascii"))
 
 ```python
 import sys
-from wormhole.transcribe import Receiver
+from wormhole.transcribe import Wormhole
 from wormhole.public_relay import RENDEZVOUS_RELAY
 mydata = b"receiver's data"
 code = sys.argv[1]
-r = Receiver("appid", RENDEZVOUS_RELAY)
+r = Wormhole("appid", RENDEZVOUS_RELAY)
 r.set_code(code)
 theirdata = r.get_data(mydata)
 print("Their data: %s" % theirdata.decode("ascii"))
@@ -57,9 +79,9 @@ The Twisted-friendly flow looks like this:
 ```python
 from twisted.internet import reactor
 from wormhole.public_relay import RENDEZVOUS_RELAY
-from wormhole.twisted.transcribe import SymmetricWormhole
+from wormhole.twisted.transcribe import Wormhole
 outbound_message = b"outbound data"
-w1 = SymmetricWormhole("appid", RENDEZVOUS_RELAY)
+w1 = Wormhole("appid", RENDEZVOUS_RELAY)
 d = w1.get_code()
 def _got_code(code):
     print "Invitation Code:", code
@@ -75,9 +97,10 @@ reactor.run()
 On the other side, you call `set_code()` instead of waiting for `get_code()`:
 
 ```python
-w2 = SymmetricWormhole("appid", RENDEZVOUS_RELAY)
+w2 = Wormhole("appid", RENDEZVOUS_RELAY)
 w2.set_code(code)
 d = w2.get_data(my_message)
+...
 ```
 
 You can call `d=w.get_verifier()` before `get_data()`: this will perform the
@@ -90,14 +113,14 @@ pausing.
 
 ## Generating the Invitation Code
 
-In most situations, the Initiator will call `i.get_code()` to generate the
+In most situations, the "sending" or "initiating" side will call
-invitation code. This returns a string in the form `NNN-code-words`. The
+`i.get_code()` to generate the invitation code. This returns a string in the
-numeric "NNN" prefix is the "channel id", and is a short integer allocated by
+form `NNN-code-words`. The numeric "NNN" prefix is the "channel id", and is a
-talking to the rendezvous server. The rest is a randomly-generated selection
+short integer allocated by talking to the rendezvous server. The rest is a
-from the PGP wordlist, providing a default of 16 bits of entropy. The
+randomly-generated selection from the PGP wordlist, providing a default of 16
-initiating program should display this code to the user, who should
+bits of entropy. The initiating program should display this code to the user,
-transcribe it to the receiving user, who gives it to the Receiver object by
+who should transcribe it to the receiving user, who gives it to the Receiver
-calling `r.set_code()`. The receiving program can also use
+object by calling `r.set_code()`. The receiving program can also use
 `input_code_with_completion()` to use a readline-based input function: this
 offers tab completion of allocated channel-ids and known codewords.
 
@@ -168,12 +191,12 @@ Both have defaults suitable for face-to-face realtime setup environments.
 
 TODO: only the Twisted form supports serialization so far
 
-You may not be able to hold the Initiator/Receiver object in memory for the
+You may not be able to hold the Wormhole object in memory for the whole sync
-whole sync process: maybe you allow it to wait for several days, but the
+process: maybe you allow it to wait for several days, but the program will be
-program will be restarted during that time. To support this, you can persist
+restarted during that time. To support this, you can persist the state of the
-the state of the object by calling `data = w.serialize()`, which will return
+object by calling `data = w.serialize()`, which will return a printable
-a printable bytestring (the JSON-encoding of a small dictionary). To restore,
+bytestring (the JSON-encoding of a small dictionary). To restore, use the
-use the `from_serialized(data)` classmethod (e.g. `w =
+`from_serialized(data)` classmethod (e.g. `w =
 SymmetricWormhole.from_serialized(data)`).
 
 There is exactly one point at which you can serialize the wormhole: *after*

setup.py

@@ -20,7 +20,7 @@ setup(name="magic-wormhole",
       package_data={"wormhole": ["db-schemas/*.sql"]},
       entry_points={"console_scripts":
                     ["wormhole = wormhole.scripts.runner:entry"]},
-      install_requires=["spake2==0.2", "pynacl", "requests", "argparse"],
+      install_requires=["spake2==0.3", "pynacl", "requests", "argparse"],
       test_suite="wormhole.test",
       cmdclass=commands,
       )

src/wormhole/blocking/transcribe.py

@@ -1,45 +1,20 @@
 from __future__ import print_function
-import sys, time, re, requests, json, textwrap
+import os, sys, time, re, requests, json
 from binascii import hexlify, unhexlify
-from spake2 import SPAKE2_A, SPAKE2_B
+from spake2 import SPAKE2_Symmetric
 from nacl.secret import SecretBox
 from nacl.exceptions import CryptoError
 from nacl import utils
 from .eventsource import EventSourceFollower
 from .. import __version__
 from .. import codes
-from ..errors import ServerError
+from ..errors import (ServerError, Timeout, WrongPasswordError,
+                      ReflectionAttack, UsageError)
 from ..util.hkdf import HKDF
 
 SECOND = 1
 MINUTE = 60*SECOND
 
-class Timeout(Exception):
-    pass
-
-class WrongPasswordError(Exception):
-    """
-    Key confirmation failed.
-    """
-    # or the data blob was corrupted, and that's why decrypt failed
-    def explain(self):
-        return textwrap.dedent(self.__doc__)
-
-class InitiatorWrongPasswordError(WrongPasswordError):
-    """
-    Key confirmation failed. Either your correspondent typed the code wrong,
-    or a would-be man-in-the-middle attacker guessed incorrectly. You could
-    try again, giving both your correspondent and the attacker another
-    chance.
-    """
-
-class ReceiverWrongPasswordError(WrongPasswordError):
-    """
-    Key confirmation failed. Either you typed the code wrong, or a would-be
-    man-in-the-middle attacker guessed incorrectly. You could try again,
-    giving both you and the attacker another chance.
-    """
-
 # relay URLs are:
 # GET /list                                         -> {channel-ids: [INT..]}
 # POST /allocate/SIDE                               -> {channel-id: INT}
@@ -49,16 +24,28 @@ class ReceiverWrongPasswordError(WrongPasswordError):
 # GET  /CHANNEL-ID/SIDE/poll/MSGNUM (eventsource)   -> STR, STR, ..
 # POST /CHANNEL-ID/SIDE/deallocate                  -> waiting | deleted
 
-class Common:
+class Wormhole:
-    def url(self, verb, msgnum=None):
+    motd_displayed = False
+    version_warning_displayed = False
+
+    def __init__(self, appid, relay):
+        self.appid = appid
+        self.relay = relay
+        if not self.relay.endswith("/"): raise UsageError
+        self.started = time.time()
+        self.wait = 0.5*SECOND
+        self.timeout = 3*MINUTE
+        self.side = None
+        self.code = None
+        self.key = None
+        self.verifier = None
+
+    def _url(self, verb, msgnum=None):
         url = "%s%d/%s/%s" % (self.relay, self.channel_id, self.side, verb)
         if msgnum is not None:
             url += "/" + msgnum
         return url
 
-    motd_displayed = False
-    version_warning_displayed = False
-
     def handle_welcome(self, welcome):
         if ("motd" in welcome and
             not self.motd_displayed):
@@ -81,33 +68,17 @@ class Common:
         if "error" in welcome:
             raise ServerError(welcome["error"], self.relay)
 
-    def get(self, old_msgs, verb, msgnum):
+    def _post_json(self, url, post_json=None):
-        # For now, server errors cause the client to fail. TODO: don't. This
+        # POST to a URL, parsing the response as JSON. Optionally include a
-        # will require changing the client to re-post messages when the
+        # JSON request body.
-        # server comes back up.
+        data = None
+        if post_json:
+            data = json.dumps(post_json).encode("utf-8")
+        r = requests.post(url, data=data)
+        r.raise_for_status()
+        return r.json()
 
-        # note: while this passes around msgs (plural), our callers really
+    def _allocate_channel(self):
-        # only care about the first one. we use "WHICH" and "SIDE" so that we
-        # only expect to see a single message (not our own, where "SIDE" is
-        # our own, and not messages for earlier stages, where "WHICH" is
-        # different)
-        msgs = old_msgs
-        while not msgs:
-            remaining = self.started + self.timeout - time.time()
-            if remaining < 0:
-                raise Timeout
-            #time.sleep(self.wait)
-            f = EventSourceFollower(self.url(verb, msgnum), remaining)
-            for (eventtype, data) in f.iter_events():
-                if eventtype == "welcome":
-                    self.handle_welcome(json.loads(data))
-                if eventtype == "message":
-                    msgs = [json.loads(data)["message"]]
-                    break
-            f.close()
-        return msgs
-
-    def _allocate(self):
         r = requests.post(self.relay + "allocate/%s" % self.side)
         r.raise_for_status()
         data = r.json()
@@ -116,124 +87,15 @@ class Common:
         channel_id = data["channel-id"]
         return channel_id
 
-    def _post_pake(self):
-        msg = self.sp.start()
-        post_data = {"message": hexlify(msg).decode("ascii")}
-        r = requests.post(self.url("post", "pake"), data=json.dumps(post_data))
-        r.raise_for_status()
-        other_msgs = r.json()["messages"]
-        return other_msgs
-
-    def _get_pake(self, other_msgs):
-        msgs = self.get(other_msgs, "poll", "pake")
-        pake_msg = unhexlify(msgs[0].encode("ascii"))
-        key = self.sp.finish(pake_msg)
-        return key
-
-    def _encrypt_data(self, key, data):
-        assert len(key) == SecretBox.KEY_SIZE
-        box = SecretBox(key)
-        nonce = utils.random(SecretBox.NONCE_SIZE)
-        return box.encrypt(data, nonce)
-
-    def _post_data(self, data):
-        post_data = json.dumps({"message": hexlify(data).decode("ascii")})
-        r = requests.post(self.url("post", "data"), data=post_data)
-        r.raise_for_status()
-        other_msgs = r.json()["messages"]
-        return other_msgs
-
-    def _get_data(self, other_msgs):
-        msgs = self.get(other_msgs, "poll", "data")
-        data = unhexlify(msgs[0].encode("ascii"))
-        return data
-
-    def _decrypt_data(self, key, encrypted):
-        assert len(key) == SecretBox.KEY_SIZE
-        box = SecretBox(key)
-        data = box.decrypt(encrypted)
-        return data
-
-    def _deallocate(self):
-        r = requests.post(self.url("deallocate"))
-        r.raise_for_status()
-
-    def derive_key(self, purpose, length=SecretBox.KEY_SIZE):
-        assert type(purpose) == type(b"")
-        return HKDF(self.key, length, CTXinfo=purpose)
-
-class Initiator(Common):
-    def __init__(self, appid, relay):
-        self.appid = appid
-        self.relay = relay
-        assert self.relay.endswith("/")
-        self.started = time.time()
-        self.wait = 0.5*SECOND
-        self.timeout = 3*MINUTE
-        self.side = "initiator"
-        self.key = None
-        self.verifier = None
-
-    def set_code(self, code): # used for human-made pre-generated codes
-        mo = re.search(r'^(\d+)-', code)
-        if not mo:
-            raise ValueError("code (%s) must start with NN-" % code)
-        self.channel_id = int(mo.group(1))
-        self.code = code
-        self.sp = SPAKE2_A(self.code.encode("ascii"),
-                           idA=self.appid+":Initiator",
-                           idB=self.appid+":Receiver")
-        self._post_pake()
-
     def get_code(self, code_length=2):
-        channel_id = self._allocate() # allocate channel
+        if self.code is not None: raise UsageError
+        self.side = hexlify(os.urandom(5))
+        channel_id = self._allocate_channel() # allocate channel
         code = codes.make_code(channel_id, code_length)
-        self.set_code(code)
+        self._set_code_and_channel_id(code)
+        self._start()
         return code
 
-    def _wait_for_key(self):
-        if not self.key:
-            key = self._get_pake([])
-            self.key = key
-            self.verifier = self.derive_key(self.appid+b":Verifier")
-
-    def get_verifier(self):
-        self._wait_for_key()
-        return self.verifier
-
-    def get_data(self, outbound_data):
-        self._wait_for_key()
-        try:
-            outbound_key = self.derive_key(b"sender")
-            outbound_encrypted = self._encrypt_data(outbound_key, outbound_data)
-            other_msgs = self._post_data(outbound_encrypted)
-
-            inbound_encrypted = self._get_data(other_msgs)
-            inbound_key = self.derive_key(b"receiver")
-            try:
-                inbound_data = self._decrypt_data(inbound_key,
-                                                  inbound_encrypted)
-            except CryptoError:
-                raise InitiatorWrongPasswordError
-        finally:
-            self._deallocate()
-        return inbound_data
-
-
-class Receiver(Common):
-    def __init__(self, appid, relay):
-        self.appid = appid
-        self.relay = relay
-        assert self.relay.endswith("/")
-        self.started = time.time()
-        self.wait = 0.5*SECOND
-        self.timeout = 3*MINUTE
-        self.side = "receiver"
-        self.code = None
-        self.channel_id = None
-        self.key = None
-        self.verifier = None
-
     def list_channels(self):
         r = requests.get(self.relay + "list")
         r.raise_for_status()
@@ -245,43 +107,117 @@ class Receiver(Common):
                                                 code_length)
         return code
 
-    def set_code(self, code):
+    def set_code(self, code): # used for human-made pre-generated codes
-        assert self.code is None
+        if self.code is not None: raise UsageError
-        assert self.channel_id is None
+        if self.side is not None: raise UsageError
-        self.code = code
+        self._set_code_and_channel_id(code)
-        self.channel_id = codes.extract_channel_id(code)
+        self.side = hexlify(os.urandom(5))
-        self.sp = SPAKE2_B(code.encode("ascii"),
+        self._start()
-                           idA=self.appid+":Initiator",
-                           idB=self.appid+":Receiver")
 
-    def _wait_for_key(self):
+    def _set_code_and_channel_id(self, code):
+        if self.code is not None: raise UsageError
+        mo = re.search(r'^(\d+)-', code)
+        if not mo:
+            raise ValueError("code (%s) must start with NN-" % code)
+        self.channel_id = int(mo.group(1))
+        self.code = code
+
+    def _start(self):
+        # allocate the rest now too, so it can be serialized
+        self.sp = SPAKE2_Symmetric(self.code.encode("ascii"),
+                                   idSymmetric=self.appid)
+        self.msg1 = self.sp.start()
+
+    def _post_message(self, url, msg):
+        # TODO: retry on failure, with exponential backoff. We're guarding
+        # against the rendezvous server being temporarily offline.
+        if not isinstance(msg, type(b"")): raise UsageError(type(msg))
+        resp = self._post_json(url, {"message": hexlify(msg).decode("ascii")})
+        return resp["messages"] # other_msgs
+
+    def _get_message(self, old_msgs, verb, msgnum):
+        # For now, server errors cause the client to fail. TODO: don't. This
+        # will require changing the client to re-post messages when the
+        # server comes back up.
+
+        # fire with a bytestring of the first message that matches
+        # verb/msgnum, which either came from old_msgs, or from an
+        # EventSource that we attached to the corresponding URL
+        msgs = old_msgs
+        while not msgs:
+            remaining = self.started + self.timeout - time.time()
+            if remaining < 0:
+                raise Timeout
+            #time.sleep(self.wait)
+            f = EventSourceFollower(self._url(verb, msgnum), remaining)
+            for (eventtype, data) in f.iter_events():
+                if eventtype == "welcome":
+                    self.handle_welcome(json.loads(data))
+                if eventtype == "message":
+                    msgs = [json.loads(data)["message"]]
+                    break
+            f.close()
+        return unhexlify(msgs[0].encode("ascii"))
+
+    def derive_key(self, purpose, length=SecretBox.KEY_SIZE):
+        if not isinstance(purpose, type(b"")): raise UsageError
+        return HKDF(self.key, length, CTXinfo=purpose)
+
+    def _encrypt_data(self, key, data):
+        if len(key) != SecretBox.KEY_SIZE: raise UsageError
+        box = SecretBox(key)
+        nonce = utils.random(SecretBox.NONCE_SIZE)
+        return box.encrypt(data, nonce)
+
+    def _decrypt_data(self, key, encrypted):
+        if len(key) != SecretBox.KEY_SIZE: raise UsageError
+        box = SecretBox(key)
+        data = box.decrypt(encrypted)
+        return data
+
+
+    def _get_key(self):
         if not self.key:
-            other_msgs = self._post_pake()
+            old_msgs = self._post_message(self._url("post", "pake"), self.msg1)
-            key = self._get_pake(other_msgs)
+            pake_msg = self._get_message(old_msgs, "poll", "pake")
-            self.key = key
+            self.key = self.sp.finish(pake_msg)
             self.verifier = self.derive_key(self.appid+b":Verifier")
 
     def get_verifier(self):
-        self._wait_for_key()
+        if self.code is None: raise UsageError
+        if self.channel_id is None: raise UsageError
+        self._get_key()
         return self.verifier
 
     def get_data(self, outbound_data):
-        assert self.code is not None
+        # only call this once
-        assert self.channel_id is not None
+        if self.code is None: raise UsageError
-        self._wait_for_key()
+        if self.channel_id is None: raise UsageError
-
         try:
-            outbound_key = self.derive_key(b"receiver")
+            self._get_key()
-            outbound_encrypted = self._encrypt_data(outbound_key, outbound_data)
+            return self._get_data2(outbound_data)
-            other_msgs = self._post_data(outbound_encrypted)
-
-            inbound_encrypted = self._get_data(other_msgs)
-            inbound_key = self.derive_key(b"sender")
-            try:
-                inbound_data = self._decrypt_data(inbound_key,
-                                                  inbound_encrypted)
-            except CryptoError:
-                raise ReceiverWrongPasswordError
         finally:
             self._deallocate()
-        return inbound_data
+
+    def _get_data2(self, outbound_data):
+        # Without predefined roles, we can't derive predictably unique keys
+        # for each side, so we use the same key for both. We use random
+        # nonces to keep the messages distinct, and check for reflection.
+        data_key = self.derive_key(b"data-key")
+
+        outbound_encrypted = self._encrypt_data(data_key, outbound_data)
+        msgs = self._post_message(self._url("post", "data"), outbound_encrypted)
+
+        inbound_encrypted = self._get_message(msgs, "poll", "data")
+        if inbound_encrypted == outbound_encrypted:
+            raise ReflectionAttack
+        try:
+            inbound_data = self._decrypt_data(data_key, inbound_encrypted)
+            return inbound_data
+        except CryptoError:
+            raise WrongPasswordError
+
+    def _deallocate(self):
+        # only try once, no retries
+        requests.post(self._url("deallocate"))
+        # ignore POST failure, don't call r.raise_for_status()

src/wormhole/errors.py

@@ -1,4 +1,4 @@
-import functools
+import functools, textwrap
 
 class ServerError(Exception):
     def __init__(self, message, relay):
@@ -16,3 +16,23 @@ def handle_server_error(func):
             print("Server error (from %s):\n%s" % (e.relay, e.message))
             return 1
     return _wrap
+
+class Timeout(Exception):
+    pass
+
+class WrongPasswordError(Exception):
+    """
+    Key confirmation failed. Either you or your correspondent typed the code
+    wrong, or a would-be man-in-the-middle attacker guessed incorrectly. You
+    could try again, giving both your correspondent and the attacker another
+    chance.
+    """
+    # or the data blob was corrupted, and that's why decrypt failed
+    def explain(self):
+        return textwrap.dedent(self.__doc__)
+
+class ReflectionAttack(Exception):
+    """An attacker (or bug) reflected our outgoing message back to us."""
+
+class UsageError(Exception):
+    """The programmer did something wrong."""

src/wormhole/scripts/cmd_receive_file.py

@@ -7,24 +7,24 @@ APPID = "lothar.com/wormhole/file-xfer"
 @handle_server_error
 def receive_file(args):
     # we're receiving
-    from ..blocking.transcribe import Receiver, WrongPasswordError
+    from ..blocking.transcribe import Wormhole, WrongPasswordError
     from ..blocking.transit import TransitReceiver, TransitError
     from .progress import start_progress, update_progress, finish_progress
 
     transit_receiver = TransitReceiver(args.transit_helper)
 
-    r = Receiver(APPID, args.relay_url)
+    w = Wormhole(APPID, args.relay_url)
     if args.zeromode:
         assert not args.code
         args.code = "0-"
     code = args.code
     if not code:
-        code = r.input_code("Enter receive-file wormhole code: ",
+        code = w.input_code("Enter receive-file wormhole code: ",
                             args.code_length)
-    r.set_code(code)
+    w.set_code(code)
 
     if args.verify:
-        verifier = binascii.hexlify(r.get_verifier())
+        verifier = binascii.hexlify(w.get_verifier())
         print("Verifier %s." % verifier)
 
     mydata = json.dumps({
@@ -34,7 +34,7 @@ def receive_file(args):
             },
         }).encode("utf-8")
     try:
-        data = json.loads(r.get_data(mydata).decode("utf-8"))
+        data = json.loads(w.get_data(mydata).decode("utf-8"))
     except WrongPasswordError as e:
         print("ERROR: " + e.explain(), file=sys.stderr)
         return 1
@@ -50,7 +50,7 @@ def receive_file(args):
 
     # now receive the rest of the owl
     tdata = data["transit"]
-    transit_key = r.derive_key(APPID+"/transit-key")
+    transit_key = w.derive_key(APPID+"/transit-key")
     transit_receiver.set_transit_key(transit_key)
     transit_receiver.add_their_direct_hints(tdata["direct_connection_hints"])
     transit_receiver.add_their_relay_hints(tdata["relay_connection_hints"])

src/wormhole/scripts/cmd_receive_text.py

@@ -7,25 +7,25 @@ APPID = "lothar.com/wormhole/text-xfer"
 @handle_server_error
 def receive_text(args):
     # we're receiving
-    from ..blocking.transcribe import Receiver, WrongPasswordError
+    from ..blocking.transcribe import Wormhole, WrongPasswordError
 
-    r = Receiver(APPID, args.relay_url)
+    w = Wormhole(APPID, args.relay_url)
     if args.zeromode:
         assert not args.code
         args.code = "0-"
     code = args.code
     if not code:
-        code = r.input_code("Enter receive-text wormhole code: ",
+        code = w.input_code("Enter receive-text wormhole code: ",
                             args.code_length)
-    r.set_code(code)
+    w.set_code(code)
 
     if args.verify:
-        verifier = binascii.hexlify(r.get_verifier())
+        verifier = binascii.hexlify(w.get_verifier())
         print("Verifier %s." % verifier)
 
     data = json.dumps({"message": "ok"}).encode("utf-8")
     try:
-        them_bytes = r.get_data(data)
+        them_bytes = w.get_data(data)
     except WrongPasswordError as e:
         print("ERROR: " + e.explain(), file=sys.stderr)
         return 1

src/wormhole/scripts/cmd_send_file.py

@@ -7,7 +7,7 @@ APPID = "lothar.com/wormhole/file-xfer"
 @handle_server_error
 def send_file(args):
     # we're sending
-    from ..blocking.transcribe import Initiator, WrongPasswordError
+    from ..blocking.transcribe import Wormhole, WrongPasswordError
     from ..blocking.transit import TransitSender
     from .progress import start_progress, update_progress, finish_progress
 
@@ -15,15 +15,15 @@ def send_file(args):
     assert os.path.isfile(filename)
     transit_sender = TransitSender(args.transit_helper)
 
-    i = Initiator(APPID, args.relay_url)
+    w = Wormhole(APPID, args.relay_url)
     if args.zeromode:
         assert not args.code
         args.code = "0-"
     if args.code:
-        i.set_code(args.code)
+        w.set_code(args.code)
         code = args.code
     else:
-        code = i.get_code(args.code_length)
+        code = w.get_code(args.code_length)
     other_cmd = "wormhole receive-file"
     if args.verify:
         other_cmd = "wormhole --verify receive-file"
@@ -35,7 +35,7 @@ def send_file(args):
     print()
 
     if args.verify:
-        verifier = binascii.hexlify(i.get_verifier())
+        verifier = binascii.hexlify(w.get_verifier())
         while True:
             ok = raw_input("Verifier %s. ok? (yes/no): " % verifier)
             if ok.lower() == "yes":
@@ -45,7 +45,7 @@ def send_file(args):
                       file=sys.stderr)
                 reject_data = json.dumps({"error": "verification rejected",
                                           }).encode("utf-8")
-                i.get_data(reject_data)
+                w.get_data(reject_data)
                 return 1
 
     filesize = os.stat(filename).st_size
@@ -61,7 +61,7 @@ def send_file(args):
         }).encode("utf-8")
 
     try:
-        them_bytes = i.get_data(data)
+        them_bytes = w.get_data(data)
     except WrongPasswordError as e:
         print("ERROR: " + e.explain(), file=sys.stderr)
         return 1
@@ -70,7 +70,7 @@ def send_file(args):
 
 
     tdata = them_d["transit"]
-    transit_key = i.derive_key(APPID+"/transit-key")
+    transit_key = w.derive_key(APPID+"/transit-key")
     transit_sender.set_transit_key(transit_key)
     transit_sender.add_their_direct_hints(tdata["direct_connection_hints"])
     transit_sender.add_their_relay_hints(tdata["relay_connection_hints"])

src/wormhole/scripts/cmd_send_text.py

@@ -7,17 +7,17 @@ APPID = "lothar.com/wormhole/text-xfer"
 @handle_server_error
 def send_text(args):
     # we're sending
-    from ..blocking.transcribe import Initiator, WrongPasswordError
+    from ..blocking.transcribe import Wormhole, WrongPasswordError
 
-    i = Initiator(APPID, args.relay_url)
+    w = Wormhole(APPID, args.relay_url)
     if args.zeromode:
         assert not args.code
         args.code = "0-"
     if args.code:
-        i.set_code(args.code)
+        w.set_code(args.code)
         code = args.code
     else:
-        code = i.get_code(args.code_length)
+        code = w.get_code(args.code_length)
     other_cmd = "wormhole receive-text"
     if args.verify:
         other_cmd = "wormhole --verify receive-text"
@@ -29,7 +29,7 @@ def send_text(args):
     print("")
 
     if args.verify:
-        verifier = binascii.hexlify(i.get_verifier())
+        verifier = binascii.hexlify(w.get_verifier())
         while True:
             ok = raw_input("Verifier %s. ok? (yes/no): " % verifier)
             if ok.lower() == "yes":
@@ -39,14 +39,14 @@ def send_text(args):
                       file=sys.stderr)
                 reject_data = json.dumps({"error": "verification rejected",
                                           }).encode("utf-8")
-                i.get_data(reject_data)
+                w.get_data(reject_data)
                 return 1
 
     message = args.text
     data = json.dumps({"message": message,
                        }).encode("utf-8")
     try:
-        them_bytes = i.get_data(data)
+        them_bytes = w.get_data(data)
     except WrongPasswordError as e:
         print("ERROR: " + e.explain(), file=sys.stderr)
         return 1

src/wormhole/test/test_twisted.py

@@ -1,16 +1,18 @@
 import json
 from twisted.trial import unittest
 from twisted.internet import defer
+from twisted.internet.threads import deferToThread
 from twisted.application import service
 from ..servers.relay import RelayServer
-from ..twisted.transcribe import SymmetricWormhole, UsageError
+from ..twisted.transcribe import Wormhole, UsageError
 from ..twisted.util import allocate_ports
+from ..blocking.transcribe import Wormhole as BlockingWormhole
 from .. import __version__
 #from twisted.python import log
 #import sys
 #log.startLogging(sys.stdout)
 
-class Basic(unittest.TestCase):
+class ServerBase:
     def setUp(self):
         self.sp = service.MultiService()
         self.sp.startService()
@@ -29,10 +31,11 @@ class Basic(unittest.TestCase):
     def tearDown(self):
         return self.sp.stopService()
 
+class Basic(ServerBase, unittest.TestCase):
     def test_basic(self):
         appid = "appid"
-        w1 = SymmetricWormhole(appid, self.relayurl)
+        w1 = Wormhole(appid, self.relayurl)
-        w2 = SymmetricWormhole(appid, self.relayurl)
+        w2 = Wormhole(appid, self.relayurl)
         d = w1.get_code()
         def _got_code(code):
             w2.set_code(code)
@@ -43,8 +46,8 @@ class Basic(unittest.TestCase):
         def _done(dl):
             ((success1, dataX), (success2, dataY)) = dl
             r1,r2 = dl
-            self.assertTrue(success1)
+            self.assertTrue(success1, dataX)
-            self.assertTrue(success2)
+            self.assertTrue(success2, dataY)
             self.assertEqual(dataX, "data2")
             self.assertEqual(dataY, "data1")
         d.addCallback(_done)
@@ -52,8 +55,8 @@ class Basic(unittest.TestCase):
 
     def test_fixed_code(self):
         appid = "appid"
-        w1 = SymmetricWormhole(appid, self.relayurl)
+        w1 = Wormhole(appid, self.relayurl)
-        w2 = SymmetricWormhole(appid, self.relayurl)
+        w2 = Wormhole(appid, self.relayurl)
         w1.set_code("123-purple-elephant")
         w2.set_code("123-purple-elephant")
         d1 = w1.get_data("data1")
@@ -62,8 +65,8 @@ class Basic(unittest.TestCase):
         def _done(dl):
             ((success1, dataX), (success2, dataY)) = dl
             r1,r2 = dl
-            self.assertTrue(success1)
+            self.assertTrue(success1, dataX)
-            self.assertTrue(success2)
+            self.assertTrue(success2, dataY)
             self.assertEqual(dataX, "data2")
             self.assertEqual(dataY, "data1")
         d.addCallback(_done)
@@ -71,22 +74,22 @@ class Basic(unittest.TestCase):
 
     def test_errors(self):
         appid = "appid"
-        w1 = SymmetricWormhole(appid, self.relayurl)
+        w1 = Wormhole(appid, self.relayurl)
         self.assertRaises(UsageError, w1.get_verifier)
         self.assertRaises(UsageError, w1.get_data, "data")
         w1.set_code("123-purple-elephant")
         self.assertRaises(UsageError, w1.set_code, "123-nope")
         self.assertRaises(UsageError, w1.get_code)
-        w2 = SymmetricWormhole(appid, self.relayurl)
+        w2 = Wormhole(appid, self.relayurl)
         d = w2.get_code()
         self.assertRaises(UsageError, w2.get_code)
         return d
 
     def test_serialize(self):
         appid = "appid"
-        w1 = SymmetricWormhole(appid, self.relayurl)
+        w1 = Wormhole(appid, self.relayurl)
         self.assertRaises(UsageError, w1.serialize) # too early
-        w2 = SymmetricWormhole(appid, self.relayurl)
+        w2 = Wormhole(appid, self.relayurl)
         d = w1.get_code()
         def _got_code(code):
             self.assertRaises(UsageError, w2.serialize) # too early
@@ -96,7 +99,7 @@ class Basic(unittest.TestCase):
             self.assertEqual(type(s), type(""))
             unpacked = json.loads(s) # this is supposed to be JSON
             self.assertEqual(type(unpacked), dict)
-            new_w1 = SymmetricWormhole.from_serialized(s)
+            new_w1 = Wormhole.from_serialized(s)
             d1 = new_w1.get_data("data1")
             d2 = w2.get_data("data2")
             return defer.DeferredList([d1,d2], fireOnOneErrback=False)
@@ -104,10 +107,100 @@ class Basic(unittest.TestCase):
         def _done(dl):
             ((success1, dataX), (success2, dataY)) = dl
             r1,r2 = dl
-            self.assertTrue(success1)
+            self.assertTrue(success1, dataX)
-            self.assertTrue(success2)
+            self.assertTrue(success2, dataY)
             self.assertEqual(dataX, "data2")
             self.assertEqual(dataY, "data1")
             self.assertRaises(UsageError, w2.serialize) # too late
         d.addCallback(_done)
         return d
+
+class Blocking(ServerBase, unittest.TestCase):
+    # we need Twisted to run the server, but we run the sender and receiver
+    # with deferToThread()
+
+    def test_basic(self):
+        appid = "appid"
+        w1 = BlockingWormhole(appid, self.relayurl)
+        w2 = BlockingWormhole(appid, self.relayurl)
+        d = deferToThread(w1.get_code)
+        def _got_code(code):
+            w2.set_code(code)
+            d1 = deferToThread(w1.get_data, "data1")
+            d2 = deferToThread(w2.get_data, "data2")
+            return defer.DeferredList([d1,d2], fireOnOneErrback=False)
+        d.addCallback(_got_code)
+        def _done(dl):
+            ((success1, dataX), (success2, dataY)) = dl
+            r1,r2 = dl
+            self.assertTrue(success1, dataX)
+            self.assertTrue(success2, dataY)
+            self.assertEqual(dataX, "data2")
+            self.assertEqual(dataY, "data1")
+        d.addCallback(_done)
+        return d
+
+    def test_fixed_code(self):
+        appid = "appid"
+        w1 = BlockingWormhole(appid, self.relayurl)
+        w2 = BlockingWormhole(appid, self.relayurl)
+        w1.set_code("123-purple-elephant")
+        w2.set_code("123-purple-elephant")
+        d1 = deferToThread(w1.get_data, "data1")
+        d2 = deferToThread(w2.get_data, "data2")
+        d = defer.DeferredList([d1,d2], fireOnOneErrback=False)
+        def _done(dl):
+            ((success1, dataX), (success2, dataY)) = dl
+            r1,r2 = dl
+            self.assertTrue(success1, dataX)
+            self.assertTrue(success2, dataY)
+            self.assertEqual(dataX, "data2")
+            self.assertEqual(dataY, "data1")
+        d.addCallback(_done)
+        return d
+
+    def test_errors(self):
+        appid = "appid"
+        w1 = BlockingWormhole(appid, self.relayurl)
+        self.assertRaises(UsageError, w1.get_verifier)
+        self.assertRaises(UsageError, w1.get_data, "data")
+        w1.set_code("123-purple-elephant")
+        self.assertRaises(UsageError, w1.set_code, "123-nope")
+        self.assertRaises(UsageError, w1.get_code)
+        w2 = BlockingWormhole(appid, self.relayurl)
+        d = deferToThread(w2.get_code)
+        def _done(code):
+            self.assertRaises(UsageError, w2.get_code)
+        d.addCallback(_done)
+        return d
+
+    def test_serialize(self):
+        appid = "appid"
+        w1 = BlockingWormhole(appid, self.relayurl)
+        self.assertRaises(UsageError, w1.serialize) # too early
+        w2 = BlockingWormhole(appid, self.relayurl)
+        d = deferToThread(w1.get_code)
+        def _got_code(code):
+            self.assertRaises(UsageError, w2.serialize) # too early
+            w2.set_code(code)
+            w2.serialize() # ok
+            s = w1.serialize()
+            self.assertEqual(type(s), type(""))
+            unpacked = json.loads(s) # this is supposed to be JSON
+            self.assertEqual(type(unpacked), dict)
+            new_w1 = BlockingWormhole.from_serialized(s)
+            d1 = deferToThread(new_w1.get_data, "data1")
+            d2 = deferToThread(w2.get_data, "data2")
+            return defer.DeferredList([d1,d2], fireOnOneErrback=False)
+        d.addCallback(_got_code)
+        def _done(dl):
+            ((success1, dataX), (success2, dataY)) = dl
+            r1,r2 = dl
+            self.assertTrue(success1, dataX)
+            self.assertTrue(success2, dataY)
+            self.assertEqual(dataX, "data2")
+            self.assertEqual(dataY, "data1")
+            self.assertRaises(UsageError, w2.serialize) # too late
+        d.addCallback(_done)
+        return d
+    test_serialize.skip = "not yet implemented for the blocking flavor"

src/wormhole/twisted/demo.py

@@ -1,28 +1,38 @@
-import sys
+import sys, json
 from twisted.internet import reactor
-from .transcribe import SymmetricWormhole
+from .transcribe import Wormhole
 from .. import public_relay
 
 APPID = "lothar.com/wormhole/text-xfer"
 
-w = SymmetricWormhole(APPID, public_relay.RENDEZVOUS_RELAY)
+w = Wormhole(APPID, public_relay.RENDEZVOUS_RELAY)
 
 if sys.argv[1] == "send-text":
     message = sys.argv[2]
+    data = json.dumps({"message": message}).encode("utf-8")
     d = w.get_code()
     def _got_code(code):
         print "code is:", code
-        return w.get_data(message)
+        return w.get_data(data)
     d.addCallback(_got_code)
-    def _got_data(their_data):
+    def _got_data(them_bytes):
-        print "ack:", their_data
+        them_d = json.loads(them_bytes.decode("utf-8"))
+        if them_d["message"] == "ok":
+            print "text sent"
+        else:
+            print "error sending text: %r" % (them_d,)
     d.addCallback(_got_data)
 elif sys.argv[1] == "receive-text":
     code = sys.argv[2]
     w.set_code(code)
-    d = w.get_data("ok")
+    data = json.dumps({"message": "ok"}).encode("utf-8")
-    def _got_data(their_data):
+    d = w.get_data(data)
-        print their_data
+    def _got_data(them_bytes):
+        them_d = json.loads(them_bytes.decode("utf-8"))
+        if "error" in them_d:
+            print >>sys.stderr, "ERROR: " + them_d["error"]
+            return 1
+        print them_d["message"]
     d.addCallback(_got_data)
 else:
     raise ValueError("bad command")

src/wormhole/twisted/transcribe.py

@@ -10,23 +10,13 @@ from nacl.secret import SecretBox
 from nacl.exceptions import CryptoError
 from nacl import utils
 from spake2 import SPAKE2_Symmetric
-from .eventsource import ReconnectingEventSource
+from .eventsource_twisted import ReconnectingEventSource
 from .. import __version__
 from .. import codes
-from ..errors import ServerError
+from ..errors import (ServerError, WrongPasswordError,
+                      ReflectionAttack, UsageError)
 from ..util.hkdf import HKDF
 
-class WrongPasswordError(Exception):
-    """
-    Key confirmation failed.
-    """
-
-class ReflectionAttack(Exception):
-    """An attacker (or bug) reflected our outgoing message back to us."""
-
-class UsageError(Exception):
-    """The programmer did something wrong."""
-
 @implementer(IBodyProducer)
 class DataProducer:
     def __init__(self, data):
@@ -43,7 +33,10 @@ class DataProducer:
         pass
 
 
-class SymmetricWormhole:
+class Wormhole:
+    motd_displayed = False
+    version_warning_displayed = False
+
     def __init__(self, appid, relay):
         self.appid = appid
         self.relay = relay
@@ -53,6 +46,61 @@ class SymmetricWormhole:
         self.key = None
         self._started_get_code = False
 
+    def _url(self, verb, msgnum=None):
+        url = "%s%d/%s/%s" % (self.relay, self.channel_id, self.side, verb)
+        if msgnum is not None:
+            url += "/" + msgnum
+        return url
+
+    def handle_welcome(self, welcome):
+        if ("motd" in welcome and
+            not self.motd_displayed):
+            motd_lines = welcome["motd"].splitlines()
+            motd_formatted = "\n ".join(motd_lines)
+            print("Server (at %s) says:\n %s" % (self.relay, motd_formatted),
+                  file=sys.stderr)
+            self.motd_displayed = True
+
+        # Only warn if we're running a release version (e.g. 0.0.6, not
+        # 0.0.6-DISTANCE-gHASH). Only warn once.
+        if ("-" not in __version__ and
+            not self.version_warning_displayed and
+            welcome["current_version"] != __version__):
+            print("Warning: errors may occur unless both sides are running the same version", file=sys.stderr)
+            print("Server claims %s is current, but ours is %s"
+                  % (welcome["current_version"], __version__), file=sys.stderr)
+            self.version_warning_displayed = True
+
+        if "error" in welcome:
+            raise ServerError(welcome["error"], self.relay)
+
+    def _post_json(self, url, post_json=None):
+        # POST to a URL, parsing the response as JSON. Optionally include a
+        # JSON request body.
+        p = None
+        if post_json:
+            data = json.dumps(post_json).encode("utf-8")
+            p = DataProducer(data)
+        d = self.agent.request("POST", url, bodyProducer=p)
+        def _check_error(resp):
+            if resp.code != 200:
+                raise web_error.Error(resp.code, resp.phrase)
+            return resp
+        d.addCallback(_check_error)
+        d.addCallback(web_client.readBody)
+        d.addCallback(lambda data: json.loads(data))
+        return d
+
+    def _allocate_channel(self):
+        url = self.relay + "allocate/%s" % self.side
+        d = self._post_json(url)
+        def _got_channel(data):
+            if "welcome" in data:
+                self.handle_welcome(data["welcome"])
+            return data["channel-id"]
+        d.addCallback(_got_channel)
+        return d
+
     def get_code(self, code_length=2):
         if self.code is not None: raise UsageError
         if self._started_get_code: raise UsageError
@@ -67,16 +115,6 @@ class SymmetricWormhole:
         d.addCallback(_got_channel_id)
         return d
 
-    def _allocate_channel(self):
-        url = self.relay + "allocate/%s" % self.side
-        d = self.post(url)
-        def _got_channel(data):
-            if "welcome" in data:
-                self.handle_welcome(data["welcome"])
-            return data["channel-id"]
-        d.addCallback(_got_channel)
-        return d
-
     def set_code(self, code):
         if self.code is not None: raise UsageError
         if self.side is not None: raise UsageError
@@ -95,8 +133,7 @@ class SymmetricWormhole:
     def _start(self):
         # allocate the rest now too, so it can be serialized
         self.sp = SPAKE2_Symmetric(self.code.encode("ascii"),
-                                   idA=self.appid+":SymmetricA",
+                                   idSymmetric=self.appid)
-                                   idB=self.appid+":SymmetricB")
         self.msg1 = self.sp.start()
 
     def serialize(self):
@@ -124,60 +161,21 @@ class SymmetricWormhole:
         self.msg1 = d["msg1"].decode("hex")
         return self
 
-    motd_displayed = False
+    def _post_message(self, url, msg):
-    version_warning_displayed = False
-
-    def handle_welcome(self, welcome):
-        if ("motd" in welcome and
-            not self.motd_displayed):
-            motd_lines = welcome["motd"].splitlines()
-            motd_formatted = "\n ".join(motd_lines)
-            print("Server (at %s) says:\n %s" % (self.relay, motd_formatted),
-                  file=sys.stderr)
-            self.motd_displayed = True
-
-        # Only warn if we're running a release version (e.g. 0.0.6, not
-        # 0.0.6-DISTANCE-gHASH). Only warn once.
-        if ("-" not in __version__ and
-            not self.version_warning_displayed and
-            welcome["current_version"] != __version__):
-            print("Warning: errors may occur unless both sides are running the same version", file=sys.stderr)
-            print("Server claims %s is current, but ours is %s"
-                  % (welcome["current_version"], __version__), file=sys.stderr)
-            self.version_warning_displayed = True
-
-        if "error" in welcome:
-            raise ServerError(welcome["error"], self.relay)
-
-    def url(self, verb, msgnum=None):
-        url = "%s%d/%s/%s" % (self.relay, self.channel_id, self.side, verb)
-        if msgnum is not None:
-            url += "/" + msgnum
-        return url
-
-    def post(self, url, post_json=None):
         # TODO: retry on failure, with exponential backoff. We're guarding
         # against the rendezvous server being temporarily offline.
-        p = None
+        if not isinstance(msg, type(b"")): raise UsageError(type(msg))
-        if post_json:
+        d = self._post_json(url, {"message": hexlify(msg).decode("ascii")})
-            data = json.dumps(post_json).encode("utf-8")
+        d.addCallback(lambda resp: resp["messages"]) # other_msgs
-            p = DataProducer(data)
-        d = self.agent.request("POST", url, bodyProducer=p)
-        def _check_error(resp):
-            if resp.code != 200:
-                raise web_error.Error(resp.code, resp.phrase)
-            return resp
-        d.addCallback(_check_error)
-        d.addCallback(web_client.readBody)
-        d.addCallback(lambda data: json.loads(data))
         return d
 
-    def _get_msgs(self, old_msgs, verb, msgnum):
+    def _get_message(self, old_msgs, verb, msgnum):
-        # fire with a list of messages that match verb/msgnum, which either
+        # fire with a bytestring of the first message that matches
-        # came from old_msgs, or from an EventSource that we attached to the
+        # verb/msgnum, which either came from old_msgs, or from an
-        # corresponding URL
+        # EventSource that we attached to the corresponding URL
         if old_msgs:
-            return defer.succeed(old_msgs)
+            msg = unhexlify(old_msgs[0].encode("ascii"))
+            return defer.succeed(msg)
         d = defer.Deferred()
         msgs = []
         def _handle(name, data):
@@ -186,28 +184,30 @@ class SymmetricWormhole:
             if name == "message":
                 msgs.append(json.loads(data)["message"])
                 d.callback(None)
-        es = ReconnectingEventSource(None, lambda: self.url(verb, msgnum),
+        es = ReconnectingEventSource(None, lambda: self._url(verb, msgnum),
                                      _handle)#, agent=self.agent)
         es.startService() # TODO: .setServiceParent(self)
         es.activate()
         d.addCallback(lambda _: es.deactivate())
         d.addCallback(lambda _: es.stopService())
-        d.addCallback(lambda _: msgs)
+        d.addCallback(lambda _: unhexlify(msgs[0].encode("ascii")))
         return d
 
     def derive_key(self, purpose, length=SecretBox.KEY_SIZE):
-        assert self.key is not None # call after get_verifier() or get_data()
+        if self.key is None:
-        assert type(purpose) == type(b"")
+            # call after get_verifier() or get_data()
+            raise UsageError
+        if not isinstance(purpose, type(b"")): raise UsageError
         return HKDF(self.key, length, CTXinfo=purpose)
 
     def _encrypt_data(self, key, data):
-        assert len(key) == SecretBox.KEY_SIZE
+        if len(key) != SecretBox.KEY_SIZE: raise UsageError
         box = SecretBox(key)
         nonce = utils.random(SecretBox.NONCE_SIZE)
         return box.encrypt(data, nonce)
 
     def _decrypt_data(self, key, encrypted):
-        assert len(key) == SecretBox.KEY_SIZE
+        if len(key) != SecretBox.KEY_SIZE: raise UsageError
         box = SecretBox(key)
         data = box.decrypt(encrypted)
         return data
@@ -217,11 +217,9 @@ class SymmetricWormhole:
         # TODO: prevent multiple invocation
         if self.key:
             return defer.succeed(self.key)
-        data = {"message": hexlify(self.msg1).decode("ascii")}
+        d = self._post_message(self._url("post", "pake"), self.msg1)
-        d = self.post(self.url("post", "pake"), data)
+        d.addCallback(lambda msgs: self._get_message(msgs, "poll", "pake"))
-        d.addCallback(lambda j: self._get_msgs(j["messages"], "poll", "pake"))
+        def _got_pake(pake_msg):
-        def _got_pake(msgs):
-            pake_msg = unhexlify(msgs[0].encode("ascii"))
             key = self.sp.finish(pake_msg)
             self.key = key
             self.verifier = self.derive_key(self.appid+b":Verifier")
@@ -240,6 +238,7 @@ class SymmetricWormhole:
         if self.code is None: raise UsageError
         d = self._get_key()
         d.addCallback(self._get_data2, outbound_data)
+        d.addBoth(self._deallocate)
         return d
 
     def _get_data2(self, key, outbound_data):
@@ -247,12 +246,12 @@ class SymmetricWormhole:
         # for each side, so we use the same key for both. We use random
         # nonces to keep the messages distinct, and check for reflection.
         data_key = self.derive_key(b"data-key")
+
         outbound_encrypted = self._encrypt_data(data_key, outbound_data)
-        data = {"message": hexlify(outbound_encrypted).decode("ascii")}
+        d = self._post_message(self._url("post", "data"), outbound_encrypted)
-        d = self.post(self.url("post", "data"), data)
+
-        d.addCallback(lambda j: self._get_msgs(j["messages"], "poll", "data"))
+        d.addCallback(lambda msgs: self._get_message(msgs, "poll", "data"))
-        def _got_data(msgs):
+        def _got_data(inbound_encrypted):
-            inbound_encrypted = unhexlify(msgs[0].encode("ascii"))
             if inbound_encrypted == outbound_encrypted:
                 raise ReflectionAttack
             try:
@@ -261,11 +260,10 @@ class SymmetricWormhole:
             except CryptoError:
                 raise WrongPasswordError
         d.addCallback(_got_data)
-        d.addBoth(self._deallocate)
         return d
 
     def _deallocate(self, res):
         # only try once, no retries
-        d = self.agent.request("POST", self.url("deallocate"))
+        d = self.agent.request("POST", self._url("deallocate"))
         d.addBoth(lambda _: res) # ignore POST failure, pass-through result
         return d