Abstract. Encapsulating messages in onions 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 can be highly vulnerable to attacks by 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. A repetitive attack was examined for mix-networks. However, none of the countermeasures designed is suitable for onion-routing. In this paper we propose an "onion-like" encoding design based on universal reencryption. The onions constructed in this way can be used in a protocol that achieves the same goals as the classical onions, however, at the same time we achieve immunity against a repetitive attack. Even if an adversary disturbs communication and prevents processing a message somewhere on the onion path, it is easy to identify the malicious server performing the attack and provide an evidence of its illegal behavior.
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