Secure Verification of Location Claims

1
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.

2
Secure Verification of Location Claims

• Let be a set of Verifiers V, Prover p and Region
  R.
• location determination problem verifier
  actively seeks provers 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.

3
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.

4
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)

5
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)

6
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

7
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

8
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
9
Secure Verification of Location Claims

• Non-uniform Regionscontinue.
• Let ROA(?p) region where at least one verifier
  node can prove location claim.
• ROA(?p) ?ROA(v,?p)
• More than one verifier might be eligible.
• Prover does not gain any advantage by selecting a
  different verifier.
• Coverage ROA(?p) / R

10
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.

11
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.

12
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)

13
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