When A Small Leak Sinks A Great Ship: Deanonymizing Tor Hidden Service Users Through Bitcoin Transactions Analysis


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When A Small Leak Sinks A Great Ship: Deanonymizing Tor Hidden Service Users Through Bitcoin Transactions Analysis

ABSTRACT

With the rapid increase of threats on the Internet, people are continuously
seeking privacy and anonymity. Services such as Bitcoin and
Tor were introduced to provide anonymity for online transactions
and Web browsing. Due to its pseudonymity model, Bitcoin lacks
retroactive operational security, which means historical pieces of
information could be used to identify a certain user. We investigate
the feasibility of deanonymizing users of Tor hidden services who
rely on Bitcoin as a payment method by exploiting public information
leaked from online social networks, the Blockchain, and onion
websites. This, for example, allows an adversary to link a user with
@alice Twitter address to a Tor hidden service with private.onion
address by finding at least one past transaction in the Blockchain
that involves their publicly declared Bitcoin addresses.
To demonstrate the feasibility of this deanonymization attack,
we carried out a real-world experiment simulating a passive, limited
adversary. We crawled 1.5K hidden services and collected 88
unique Bitcoin addresses. We then crawled 5B tweets and 1M BitcoinTalk
forum pages and collected 4.2K and 41K unique Bitcoin
addresses, respectively. Each user address was associated with an
online identity along with its public profile information. By analyzing
the transactions in the Blockchain, we were able to link 125
unique users to 20 Tor hidden services, including sensitive ones,
such as The Pirate Bay and Silk Road. We also analyzed two case
studies in detail to demonstrate the implications of the resulting
information leakage on user anonymity. In particular, we confirm
that Bitcoin addresses should always be considered exploitable, as
they can be used to deanonymize users retroactively. This is especially
important for Tor hidden service users who actively seek and
expect privacy and anonymity.