Abstract
Tor is the de facto standard used for anonymous communication over the Internet. Despite its wide usage, Tor does not guarantee sender anonymity, even in a threat model in which the attacker passively observes the traffic at the first Tor router. In a more severe threat model, in which the adversary can perform traffic analysis on the first and last Tor routers, relationship anonymity is also broken. In this paper, we propose a new protocol extending Tor to achieve sender anonymity (and then relationship anonymity) in the most severe threat model, allowing a global passive adversary to monitor all of the traffic in the network. We compare our proposal with Tor through the lens of security in an incremental threat model. The experimental validation shows that the price we have to pay in terms of network performance is tolerable.
Highlights
V.; Idone, M.F.; Labrini, C.; Lazzaro, S.The Tor overlay network [1] is the most popular anonymous communication protocol used for low-latency network applications
The aim of Tor, as in general happens for an anonymous communication network, is to prevent the adversary from detecting that a given sender is communicating with a given recipient
As we focus on the part of the proposal that plays the role of add-on, with respect to the existing Tor system, we do not consider the Tor communication occurring outside the system, between the proxy node and the destination
Summary
V.; Idone, M.F.; Labrini, C.; Lazzaro, S.The Tor overlay network [1] is the most popular anonymous communication protocol used for low-latency network applications. Each relay node receives its message from the preceding one and forwards it to the until the destination is reached. The message is wrapped through layered encryption, which the sender can apply by knowing the cryptographic keys of all the relay nodes of the route. The message with only one layer of encryption reaches the destination According to this scheme, each node in the route only knows the address of the preceding node and the address of the node. Sender anonymity is not supported if we allow the adversary to control the first relay node. The Tor network is an overlay network, based on TCP/TLS connections, consisting of multiple relay routers called Onion routers (OR). The OP contacts periodically a trusted server called Directory
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