Provably Avoiding Geographic Regions for Tor's Onion Services

DeTorOS enables provable geographic avoidance for Tor onion services by running a TEE-backed Bento function as a trusted middlebox: both the client and the onion service upload their respective 3-hop circuit halves to this enclave, which computes the never-once or never-twice avoidance proof without revealing either party's circuit to the other.

§3 defense flow-correlationwebsite-fingerprint generic

Computing a never-once avoidance proof for a 6-hop onion-service circuit takes an average of 64.85 seconds — incurred once at connection setup — because the system must collect round-trip timing measurements across all six relays before running the geographic proof; SGX execution overhead is nominal, and the paper notes that lower-RTT circuits (more likely to be DeTorOS-compliant) reduce subsequent data-transfer latency.

§5.3 evaluation flow-correlation generic

Never-twice provable avoidance succeeds for 72.4% of sampled source-destination pairs on 6-hop onion-service circuits, compared to approximately 98% on the original 3-hop DeTor circuits; the degradation arises because the additional hops increase round-trip time, making it harder to rule out forbidden-region traversal via speed-of-light bounds.

§5.2 evaluation flow-correlation generic

DeTorOS's security relies on the honest-but-curious model: if the onion service refuses to participate or lies about its circuit, the client receives no avoidance guarantee. The paper explicitly flags this as an open limitation and notes it cannot be closed without either requiring a TEE on the onion service side or fundamental protocol changes.

§6 defense active-probing generic

Tor's built-in country-exclusion mechanism is unreliable: circuits configured to exclude US Tor nodes only actually bypassed the US 12% of the time, motivating provably-avoidant circuit construction.

§1 evaluation flow-correlation generic