Secure Verification of Location Claims

Secure Verification of Location Claims • In the physical world, identity is not the only thing that matters. • Physical location of the requester plays an important role in determining access rights. • Secure Verification of Location Claims comes natural in the physical world but not in information systems. • Location verification enables the Secure Verification of Location Claims. • Secure Verification of Location Claims benefits: • It is Natural . • No need to establish shared secrets in advance. By Alvaro E. Escobar

.p .v R Secure Verification of Location Claims • Let be a set of Verifiers V, Prover p and Region R. • location determination problem : verifier actively seeks prover’s exact location. • In-region verification problem : prover claims a location and verifier accepts or rejects it. • In-region verification problem is easier to tackle. • p claims to be in R and v ∈ V accepts or rejects. By Alvaro E. Escobar

Secure Verification of Location Claims • Model Assumptions: • No attempt to verify exact location of the prover. • Attempt t verify location claims for regions R near V. • Verifier and prover communicate using RF (radio frequency at the speed of light ) and sound (ultrasound at the speed of sound). • Prover must be able to bound its processing delay (time to digest signal). • Prover and verifier know region R a priori. By Alvaro E. Escobar

Secure Verification of Location Claims • Model Protocol • Does not require Cryptography • Does not require time synchronization • Does not require any prover – verifier agreement. • Suitable for low-cost sensor networks (low CPU and Memory reqs.). • Uses Time-of-Flight to estimate distance. • p ---RF--- v : p reports location l • v ---RF--- p : v sends nonce N (at light speed c) • p --Sound- v : p sends nonce N (at sound speed s) v accepts location claim iff: l≤ R AND elapsed time ≤ d( v , l ) . (c-1 + s-1) By Alvaro E. Escobar

Secure Verification of Location Claims • Possible Attacks • Prover tries to cheat by delaying response. • Not good. Will appear to be further away. • Prover tries to cheat by starting response transmission early. • Not possible. Nonce is randomly generated and must be known before response. • p ---RF--- v : p reports location l • v ---RF--- p : v sends nonce N (at light speed c) • p --Sound- v : p sends nonce N (at sound speed s) v accepts location claim iff: l≤ R AND elapsed time ≤ d( v , l ) . (c-1 + s-1) By Alvaro E. Escobar

Secure Verification of Location Claims • Processing Delay • Prover requires some time (∆p) to process nonce N. • Prover is aware of its ∆p and reports it to the verifier. • p ---RF--- v : p reports location l and ∆p • v ---RF--- p : v sends nonce N (at light speed c) • p --Sound- v : p sends nonce N (after ∆p seconds) v accepts location claim iff: l≤ R AND elapsed time ≤ d( v , l ) . (c-1 + s-1) + ∆p By Alvaro E. Escobar

.p l≤ R - s∆p .v R Secure Verification of Location Claims • Possible Attacks….again. • Prover tries to cheat by reporting location l at border of region R and overstating processing delay ∆p. • Verifier shrinks allowable region by s.∆p. • ROA(v,∆p) : Region Of Acceptance where location claims are permitted by v if the claimed processing delay is ∆p. • ROA(v,0) = R By Alvaro E. Escobar

Secure Verification of Location Claims • Non-uniform Regions • ROA must be a circle since signals travel at the same speed in all directions. • ROA must be wholly contained in region R so as to not accept a location claim outside of R. • ROA should be largest circle that fits within R. ROA(v,0) .p .v ROA(v,∆p) R By Alvaro E. Escobar

ROA(∆p) .v .p .v .v R Secure Verification of Location Claims • Non-uniform Regions…continue. • Let ROA(∆p) region where at least one verifier node can prove location claim. • ROA(∆p) = ỤROA(v,∆p) • More than one verifier might be eligible. • Prover does not gain any advantage by selecting a different verifier. • Coverage = ROA(∆p) / R By Alvaro E. Escobar

Secure Verification of Location Claims • Possible Attacks….once more. • “remote actuation” : complice inside R helps remote attacker. • Low-delay remote actuation of sonic signals is infeasible. By Alvaro E. Escobar

ROA(∆p) .v .p .v .v R Secure Verification of Location Claims • Rejected Variants: • (radio, sound)  (radio, radio) • Error term ∆p.c would be very large (may exceed R and verifier may not accept location claims at all. • (radio, sound)  (sound, radio) or (sound, sound) • May attack with laser-based “remote bugging” of sound. By Alvaro E. Escobar

ROA(∆p) .v .p .v .v R Secure Verification of Location Claims • Protocol Variant: • Keyed Echo Protocol • All verifiers and a prover share a key, therefore verifier can verify that a particular prover is inside R. • p ---RF--- v : p reports location l and ∆p • v ---RF--- p : v sends nonce N (at light speed c) • p --Sound- v : p sends nonce N (after ∆p seconds) By Alvaro E. Escobar

Secure Verification of Location Claims • Future Work: • More precise region verification. • Location-limited channels : Comm. Mechanism restricted to short range. • GPS (Global Positioning System) : Do not address security By Alvaro E. Escobar

Secure Verification of Location Claims