Onion Routing Based On Universal Re--Encryption 
                Immune Against Repetitive Attack

      Marcin Gomulkiewicz, Marek Klonowski, Miroslaw Kutylowski

Onion-Routing  is  one  of  the  major  techniques  providing  anonymous
communication in computer networks. To some extent, it provides security
against traffic analysis by a passive adversary. However, it seems to be
highly vulnerable to attacks of an active adversary. For  instance,  the
adversary may perform a simple so--called repetitive attack: a malicious
server sends the same massage twice, then the  adversary  traces  places
where  the  same  message  appears  twice  -- revealing the route of the
original message. Repetitive  attack  was  examined  for  mix--networks,
however  no  countermeasure designed for them can be used in the case of
onion--routing.

In this paper we propose an ``onion-like''  design  based  on  universal
re-encryption.  The  onions  constructed  in  this  way can be used in a
protocol that achieves the same goals as the  classical  onion  routing.
However, at the same time we achieve immunity against repetitive attack.
Even if  a  malicious  server  may  disturb  communication  and  prevent
processing  of  a  message  somewhere  on  the onion path, it is easy to
identify the malicious server performing the attack and  to  provide  an
evidence of its illegal behaviour.