Add --verify (display/check key-verifier). Not entirely usable yet.

To be useful, both sides must add -v. If the sender uses -v but the
receiver doesn't, the receiver won't show the verification string, so
the sender can't compare it to anything (and must either abort the
transfer or accept it blindly). Maybe the receiver should show the
verification string unconditionally. Maybe the sender should
indicate (in unprotected plaintext, along with the PAKE message) whether
the receiver should show it or not.

src/wormhole/blocking/transcribe.py

@@ -175,6 +175,8 @@ class Initiator(Common):
         self.wait = 0.5*SECOND
         self.timeout = 3*MINUTE
         self.side = "initiator"
+        self.key = None
+        self.verifier = None
 
     def get_code(self, code_length=2):
         self.channel_id = self._allocate() # allocate channel
@@ -185,9 +187,18 @@ class Initiator(Common):
         self._post_pake()
         return self.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):
-        key = self._get_pake([])
-        self.key = key
+        self._wait_for_key()
         try:
             outbound_key = self.derive_key(b"sender")
             outbound_encrypted = self._encrypt_data(outbound_key, outbound_data)
@@ -216,6 +227,8 @@ class Receiver(Common):
         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")
@@ -237,12 +250,21 @@ class Receiver(Common):
                            idA=self.appid+":Initiator",
                            idB=self.appid+":Receiver")
 
+    def _wait_for_key(self):
+        if not self.key:
+            other_msgs = self._post_pake()
+            key = self._get_pake(other_msgs)
+            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):
         assert self.code is not None
         assert self.channel_id is not None
-        other_msgs = self._post_pake()
-        key = self._get_pake(other_msgs)
-        self.key = key
+        self._wait_for_key()
 
         try:
             outbound_key = self.derive_key(b"receiver")

src/wormhole/scripts/cmd_receive_file.py

@@ -1,5 +1,5 @@
 from __future__ import print_function
-import sys, os, json
+import sys, os, json, binascii
 from wormhole.blocking.transcribe import Receiver, WrongPasswordError
 from wormhole.blocking.transit import TransitReceiver, TransitError
 from .progress import start_progress, update_progress, finish_progress
@@ -17,6 +17,10 @@ def receive_file(args):
                             args.code_length)
     r.set_code(code)
 
+    if args.verify:
+        verifier = binascii.hexlify(r.get_verifier())
+        print("Verifier %s." % verifier)
+
     mydata = json.dumps({
         "transit": {
             "direct_connection_hints": transit_receiver.get_direct_hints(),
@@ -30,6 +34,10 @@ def receive_file(args):
         return 1
     #print("their data: %r" % (data,))
 
+    if "error" in data:
+        print("ERROR: " + data["error"], file=sys.stderr)
+        return 1
+
     file_data = data["file"]
     filename = os.path.basename(file_data["filename"]) # unicode
     filesize = file_data["filesize"]

src/wormhole/scripts/cmd_receive_text.py

@@ -1,5 +1,5 @@
 from __future__ import print_function
-import sys, json
+import sys, json, binascii
 from wormhole.blocking.transcribe import Receiver, WrongPasswordError
 
 APPID = "lothar.com/wormhole/text-xfer"
@@ -12,6 +12,11 @@ def receive_text(args):
         code = r.input_code("Enter receive-text wormhole code: ",
                             args.code_length)
     r.set_code(code)
+
+    if args.verify:
+        verifier = binascii.hexlify(r.get_verifier())
+        print("Verifier %s." % verifier)
+
     data = json.dumps({"message": "ok"}).encode("utf-8")
     try:
         them_bytes = r.get_data(data)
@@ -19,4 +24,7 @@ def receive_text(args):
         print("ERROR: " + e.explain(), file=sys.stderr)
         return 1
     them_d = json.loads(them_bytes.decode("utf-8"))
+    if "error" in them_d:
+        print("ERROR: " + them_d["error"], file=sys.stderr)
+        return 1
     print(them_d["message"])

src/wormhole/scripts/cmd_send_file.py

@@ -1,5 +1,5 @@
 from __future__ import print_function
-import os, sys, json
+import os, sys, json, binascii
 from wormhole.blocking.transcribe import Initiator, WrongPasswordError
 from wormhole.blocking.transit import TransitSender
 from .progress import start_progress, update_progress, finish_progress
@@ -18,6 +18,20 @@ def send_file(args):
     print("Wormhole code is '%s'" % code)
     print()
 
+    if args.verify:
+        verifier = binascii.hexlify(i.get_verifier())
+        while True:
+            ok = raw_input("Verifier %s. ok? (yes/no): " % verifier)
+            if ok.lower() == "yes":
+                break
+            if ok.lower() == "no":
+                print("verification rejected, abandoning transfer",
+                      file=sys.stderr)
+                reject_data = json.dumps({"error": "verification rejected",
+                                          }).encode("utf-8")
+                i.get_data(reject_data)
+                return 1
+
     filesize = os.stat(filename).st_size
     data = json.dumps({
         "file": {

src/wormhole/scripts/cmd_send_text.py

@@ -1,19 +1,34 @@
 from __future__ import print_function
-import sys, json
+import sys, json, binascii
 from wormhole.blocking.transcribe import Initiator, WrongPasswordError
 
 APPID = "lothar.com/wormhole/text-xfer"
 
 def send_text(args):
     # we're sending
-    message = args.text
-    data = json.dumps({"message": message,
-                       }).encode("utf-8")
     i = Initiator(APPID, args.relay_url)
     code = i.get_code(args.code_length)
     print("On the other computer, please run: wormhole receive-text")
     print("Wormhole code is: %s" % code)
     print("")
+
+    if args.verify:
+        verifier = binascii.hexlify(i.get_verifier())
+        while True:
+            ok = raw_input("Verifier %s. ok? (yes/no): " % verifier)
+            if ok.lower() == "yes":
+                break
+            if ok.lower() == "no":
+                print("verification rejected, abandoning transfer",
+                      file=sys.stderr)
+                reject_data = json.dumps({"error": "verification rejected",
+                                          }).encode("utf-8")
+                i.get_data(reject_data)
+                return 1
+
+    message = args.text
+    data = json.dumps({"message": message,
+                       }).encode("utf-8")
     try:
         them_bytes = i.get_data(data)
     except WrongPasswordError as e:

src/wormhole/scripts/runner.py

@@ -20,6 +20,8 @@ g.add_argument("--transit-helper", default=public_relay.TRANSIT_RELAY,
                metavar="tcp:HOST:PORT", help="transit relay to use")
 g.add_argument("-c", "--code-length", type=int, default=2,
                metavar="WORDS", help="length of code (in bytes/words)")
+g.add_argument("-v", "--verify", action="store_true",
+               help="display (and wait for acceptance of) verification string")
 subparsers = parser.add_subparsers(title="subcommands",
                                    dest="subcommand")