r15268@tombo: nickm | 2007-12-11 18:22:52 -0500

tweaks to bridge-disbursement document


svn:r12774

doc/spec/proposals/ideas/xxx-bridge-disbursement.txt

@@ -55,6 +55,13 @@ IP-based.
       approach would also resolve the "Make sure you can't construct a
       distinct address to match an existing one" note below. -RD]
 
+        [I think, if we get a replay, we need to sen back the same
+        answer as we did the first time, not say "try again."
+        Otherwise we need to worry that an attacker can keep people
+        from getting bridges by preemtively asking for them,
+        or that an attacker may force them to prove they haven't
+        gotten any bridges by asking. -NM]
+
      [While we're at it, if we do the replay cache thing and don't need
       repeatable answers, we could just pick K random answers from the
       pool. Is it beneficial that a bridge user who knows about a clump of
@@ -68,12 +75,20 @@ IP-based.
       the difference in clumps and estimate how quickly the bridge pool
       is growing. -RD]
 
+        [Random is one more darn thing to implement; rings are already
+         there. -NM]
+
      [If we make the period P be mailbox-specific, and make it a random
       value around some mean, then we make it harder for an attacker to
       know when to try using his small army of gmail addresses to gather
       another harvest. But we also make it harder for users to know when
       they can try again. -RD]
 
+        [Letting the users know about when they can try again seems
+         worthwhile.  Otherwise users and attackers will all probe and
+         probe and probe until they get an answer.  No additional
+         security will be achieved, but bandwidth will be lost. -NM]
+
   To normalize an email address:
      Start with the RFC822 address.  Consider only the mailbox {???}
      portion of the address (username@domain).  Put this into lowercase
@@ -140,8 +155,9 @@ IP-based.
      in the ring after X.
 
      [Don't we want to compute C = HMAC(key, area) to learn what cluster
-     to answer from, and then X = HMAC(key, PS|area) to pick a point in
-     that ring? -RD]
+      to answer from, and then X = HMAC(key, PS|area) to pick a point in
+      that ring? -RD]
+
 
   Need to clarify that some HMACs are for rings, and some are for
   partitions. How rings scale is clear. How do we grow the number of