1 research outputs found
Anomalous keys in Tor relays
In its more than ten years of existence, the Tor network has seen hundreds of
thousands of relays come and go. Each relay maintains several RSA keys,
amounting to millions of keys, all archived by The Tor Project. In this paper,
we analyze 3.7 million RSA public keys of Tor relays. We (i) check if any
relays share prime factors or moduli, (ii) identify relays that use
non-standard exponents, (iii) characterize malicious relays that we discovered
in the first two steps, and (iv) develop a tool that can determine what onion
services fell prey to said malicious relays. Our experiments revealed that ten
relays shared moduli and 3,557 relays -- almost all part of a research project
-- shared prime factors, allowing adversaries to reconstruct private keys. We
further discovered 122 relays that used non-standard RSA exponents, presumably
in an attempt to attack onion services. By simulating how onion services are
positioned in Tor's distributed hash table, we identified four onion services
that were targeted by these malicious relays. Our work provides both The Tor
Project and onion service operators with tools to identify misconfigured and
malicious Tor relays to stop attacks before they pose a threat to Tor users