DUO--Onions and  Hydra--Onions 
          -- failure and adversary resistant onion protocols

        Jan Iwanik,  Marek Klonowski,  Miroslaw Kutylowski

A serious weakness of the onion protocol, one of  the  major  tools  for
anonymous  communication, is it vulnerability to network failures and/or
an adversary trying to break the communication. This is  facilitated  by
the  fact  that  each message is sent through a path of a certain length
and a failure in a single point of this path prohibits message delivery.
Since  the  path  cannot  be  too  short  in  order  to  offer anonymity
protection (at least  logarithmic  in  the  number  of  nodes),  failure
probability might be quite substantial.

The simplest solution to this problem would be to send many onions  with
the  same  message.  We  show  that  this approach can be optimized with
respect to communication overhead  and  resilience  to  failures  and/or
adversary  attacks.  We  propose  two  protocols: the first one mimics K
independent onions with a single onion. The second protocol is  designed
for the case where an adaptive adversary may destroy communication going
out of servers chosen according to the traffic observed by him. In  this
case a single message flows in a stream of K onions -- the main point is
that even when the adversary manages to kill some of these  onions,  the
stream quickly recovers to the original bandwidth -- again K onions with
this message would flow through the network.