1. PHY-Level Security Protection
Month Year
doc.: IEEE yy/xxxxr0
July 2017
PHY-Level Security Protection
Date:
Authors:
Li, Jiang, Segev, Abramovsky, et al, Intel
Abramovsky, Ghosh, Segev & Li, Intel

2. July 2017
Abstract
Previously in [1][2], we identified a threat model with two types of adversaries:
Type A 1ms response time
Type B 1us response time
In this submission, we present a scheme to detect and suppress Type B adversary attacks at PHY level
[1] Doc.: IEEE /0120r2 Intel Secured Location Threat Model
[2] Doc.: IEEE /0801r1 Intel Discussion on FTM Protection – follow up
Li, Jiang, Segev, Abramovsky, et al, Intel

3. Outline PHY-level technique to protect measurement symbols:
July 2017
Outline
PHY-level technique to protect measurement symbols:
Prevention of wrong sense of distance through detection of adversary attack:
Discarding contaminated measurements ensures security
Suppression of adversary attack:
Suppressing adversary attacks enhances robustness
Li, Jiang, Segev, Abramovsky, et al, Intel

4. Needs for High Security
July 2017
Needs for High Security
Some applications require high security
Door lock, PC lock, ATM
Spoofed measurement should be discarded to prevent property loss
Li, Jiang, Segev, Abramovsky, et al, Intel

5. HW Impersonation/Data Integrity – How to Spoof Legacy Sounding
Month Year
doc.: IEEE yy/xxxxr0
July 2017
HW Impersonation/Data Integrity – How to Spoof Legacy Sounding
L-STF & L-LTF give the timing reference to the VHT-LTF, which could be spoofed by the adversary
RSTA (AP) Transmission
NAV is set by 11a RTS CTS
Beamforming makes DATA not accessible to third parties
Add a backup slide for random sequence in 11mc
Note: Quotation of Slide 11 in [1]
Li, Jiang, Segev, Abramovsky, et al, Intel
Abramovsky, Ghosh, Segev & Li, Intel

6. MAC protection is insufficient
July 2017
MAC protection is insufficient
Although transmissions of time stamps i.e. t1, t2, t3, t4 can be encrypted, the measurements of t2 and t4 themselves are still vulnerable AP
Adversary
STA t1 t2
Spoofed 1st tap arrives before the true one t3
t4'
RTT is perceived smaller
because t4'-t1 < t4-t1 t4
Li, Jiang, Segev, Abramovsky, et al, Intel

7. Goals Detecting adversary attack ensures security
July 2017
Goals
Detecting adversary attack ensures security
Once adversary attack is detected, spoofed measurement can be discarded and further damage is prevented
Suppressing attack signals enhances resilience
Processing gain of random sounding sequence suppresses spoofing signal
Li, Jiang, Segev, Abramovsky, et al, Intel

8. July 2017
Adversary Detection
Conduct two sounding measurements within channel coherence time
Shift 2nd sounding symbols (i.e. HE-LTF or VHT-LTF) by a random CSD unknown to spoofer
Check consistency across two channel measurements
CSD e.g. 170 ns applied to HE-LTF
TF 1
UL NPD 1
NDP-A 1
DL NDP 1
TF 2
UL NPD 2
NDP-A 2
DL NDP 2
Channel measurement 1
Channel measurement 2
Li, Jiang, Segev, Abramovsky, et al, Intel

9. Procedures Transmitter: Receiver: July 2017
Transmit two sounding signals within channel coherence time e.g. 1ms
Apply CSD to 2nd sounding signal, where CSD value is known to the receiver over encrypted message so that spoofer can’t adapt to the CSD
Receiver:
Remove the CSD from each measurement, and compare the channel estimates of two adjacent measurements
Channel estimates should be consistent unless spoofing occurred
Channel estimates from 1st measurement
Channel estimates from 2nd measurement
Inconsistent
Due to spoofer
Due to user
Li, Jiang, Segev, Abramovsky, et al, Intel

10. July 2017
Discussions
Spoofing detection by CSD requires almost no implementation changes
CSD is currently used in legacy transmitter and receiver. For example, CSD is compensated before channel interpolation in 11n/ac/ax
Adversary attack can be detected but can’t be suppressed by random CSD
Li, Jiang, Segev, Abramovsky, et al, Intel

11. Suppression of Adversary Attack — Random sounding symbols
July 2017
Suppression of Adversary Attack — Random sounding symbols
Replace existing sounding signal (i.e. LTF binary sequence) by a random binary sequence unknown to spoofer
Sequence generation key is exchanged and encrypted before measurement
L-STF, L-LTF, L-SIG,
RL-SIG, HE-SIG-A
HE-STF
Random BPSK sequence
+1, -1,+1, +1, +1, -1, -1, …
Li, Jiang, Segev, Abramovsky, et al, Intel

12. Suppressed Spoofing Impact
July 2017
Suppressed Spoofing Impact
Spoofed 1st tap
True 1st tap
Noise level
With Legacy LTF symbols
With random sounding symbols
Concentrated, high power spoofed taps
Spread, low power spoofed taps
Li, Jiang, Segev, Abramovsky, et al, Intel

13. July 2017
20 dB Suppression
Suppress spoofed 1st tap by about 20 dB for 80 MHz sounding
True 1st tap
Spoofed 1st tap
Li, Jiang, Segev, Abramovsky, et al, Intel

14. Requirements for Random Sounding Signal
July 2017
Requirements for Random Sounding Signal
Strong security protection
A large amount of sounding signals to choose
Easy implementation
BPSK modulation and minimum storage
Support for long distance ranging
Low PAPR
Scalable protection
Nice tradeoff between security and overhead
Li, Jiang, Segev, Abramovsky, et al, Intel

15. Golay Sequences Golay sequences have low PAPR
July 2017
Golay Sequences
Golay sequences have low PAPR
About the same as 11ax LTF
Golay sequences can be easily generated
Duplication, shift, and sign change
512 sequences can be generated for 80MHz 1x sounding
The odd for the adversary is below 2 ×10-3 per sounding
Li, Jiang, Segev, Abramovsky, et al, Intel

16. Loading Golay Sequence to Subcarriers
July 2017
Loading Golay Sequence to Subcarriers
Slight puncturing is applied to Golay sequence for accommodating guard subcarriers
Golay sequence, a complementary pair
Li, Jiang, Segev, Abramovsky, et al, Intel

17. Easy Generation Using Concatenation
July 2017
Easy Generation Using Concatenation
Long Golay sequence can be generated by concatenating two short sequences
+1, +1
+1, -1 [ ] +
+1, +1
+1, -1 -
+1, +1
- [+1, -1]
[+1, +1, +1, -1], [+1, +1 -1, +1]
[+1, +1, +1, -1], [-1, -1, +1, -1]
Li, Jiang, Segev, Abramovsky, et al, Intel

18. Easy Generation Using Interleaving and Reversion
July 2017
Easy Generation Using Interleaving and Reversion
Generate new long sequence by interleaving two short ones
Generate new sequence by reversing the order of one
Two short sequences a b c d A B C D
Interleave a A b B c C d D a -A b -B c -C d -D
Reversion -D d -C c -B b -A a D d C c B b A a
Li, Jiang, Segev, Abramovsky, et al, Intel

19. Length 2K Golay Sequences
July 2017
Length 2K Golay Sequences
2K+1 sequences with length 2K
512 sequences with length 256
Large distances among generated sequences
Concatenation, interleaving, and reversion generate orthogonal sequences, respectively
Cross correlation among sequences is either 0 or 1/4
Li, Jiang, Segev, Abramovsky, et al, Intel

20. Higher Security by 4x LTF
July 2017
Higher Security by 4x LTF
4x LTF quadruples the number of sounding sequences
2048 for 80MHz at the cost of 10 us sounding time
4.0 μs
13.6 μs
1x LTF,
512 sequences
4x LTF,
2048 sequences
Li, Jiang, Segev, Abramovsky, et al, Intel

21. Higher Security by Multiple Measurements
July 2017
Higher Security by Multiple Measurements
Each measurement independently choose a sounding sequence
Sequence space increases exponentially with the number of measurements conducted within the channel coherence time
The chance left for the adversary is below 4 ×10-6 for passing three contiguous measurements
Independent sounding sequences
TF 1
UL NPD 1 …
TF 2
UL NPD 2 …
TF 3
UL NPD 3 …
Measurement 1
Measurement 2
Measurement 3
Li, Jiang, Segev, Abramovsky, et al, Intel

22. July 2017
PAPR for 80 MHz Sounding
0.5 dB better than 11ax LTF and 3.5 dB better than fully random BPSK sounding sequence
Li, Jiang, Segev, Abramovsky, et al, Intel

23. July 2017
PAPR for 40 MHz Sounding
0.3 dB worse than 11ax LTF and 2.8 dB better than fully random BPSK sounding sequence
Li, Jiang, Segev, Abramovsky, et al, Intel

24. July 2017
PAPR for 20 MHz Sounding
0.3 dB worse than 11ax LTF and 2.5 dB better than fully random binary sounding
Li, Jiang, Segev, Abramovsky, et al, Intel

25. July 2017
Summary
MAC protection is insufficient for preventing Type B spoofing and PHY protection is needed
Type B spoofing can be detected by using CSD unknown to spoofer
Type B spoofing can be suppressed by using randomized sounding signal
Sounding sequences, whose PAPRs are comparable to 11ax LTF, can be easily generated
Li, Jiang, Segev, Abramovsky, et al, Intel

26. July 2017
Backup
Li, Jiang, Segev, Abramovsky, et al, Intel

27. Random Sounding Sequence for 11mc
Month Year
doc.: IEEE yy/xxxxr0
July 2017
Random Sounding Sequence for 11mc
Replace VHT-LTF by a new VHTm-LTF
BPSK sounding sequence is replaced
Only 11mc devices can read VHT-SIG-B and DATA
Although legacy devices can’t read the VHT-SIG-B and DATA, it should be fine
NAV is usually set by legacy PPDU e.g. 11a RTS/CTS
Legacy devices don’t need to read the duration field in the DATA
L-STF
L-LTF
L-SIG
VHT-SIG-A
VHT-STF
VTHm-LTF
VHT-SIG-B
DATA
Li, Jiang, Segev, Abramovsky, et al, Intel
Abramovsky, Ghosh, Segev & Li, Intel

28. Additional Suppression to Adversary
July 2017
Additional Suppression to Adversary
Instead of 1x LTF symbol duration, 4x LTF symbol duration may be used
6 dB processing gain
Instead of 1 OFDM symbol, the random sounding signal may spread over 8 OFDM symbols
9 dB processing gain
Li, Jiang, Segev, Abramovsky, et al, Intel