  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.
