1. Functional Requirement for Secure Ranging
Month Year
file name: Broadcom -- Security Enhancement to FTM
Functional Requirement for Secure Ranging
Date:
Authors:
Qi Wang, et.al., Broadcom
Qi Wang, et.al., Broadcom

2. Abstract
This document proposes an additional function requirement for az.
Qi Wang, et.al., Broadcom

3. Security Limitation of Current FTM Ranging Protocol
Some uses cases require security for ranging
Proximity detection to point of sale (e.g.,Starbucks)
Unlock assistance to personal laptop or tablet
Unlock your car
Unlock a locker at sports facility
Serve as entry ticket, e.g., concert, sports event
Alternative access for building, e.g., in lieu of ID cards
The current FTM ranging protocol, as defined in IEEE REVmc D8.0 [1], lacks security protection of the RTT measurements and may be easily compromised.
Qi Wang, et.al., Broadcom

4. Security Issue of FTM
STA1
(Responding STA)
STA2
(Initiating STA)
FTM Request
According to [1], the FTM frames and Ack frames are not protected.
A malicious device can transmit fake Ack frames, which pretend to be the Ack frames from the Initiating STA, to the Responding STA.
Because an Ack is transmitted within an SIFS, the authentic Ack arrives in the middle of the fake Ack reception at the Responding STA. An implementation uses implementation specific criteria to decide whether to declare a collision (and abandon the t4_m capturing) or to decode either the Fake Ack or the Authentic Ack.
Using the implementation specific criteria, when the fake Ack is decoded successfully, the Responding STA obtains the wrong t4_m and includes it in the payload of the subsequent FTM frame, which causes the Initiating STA to derive the wrong RTT.
Ack
FTM_m payload contains [t1_(m-1), t4_(m-1)]
t1_m
t2_m
Fake Ack
t4_m’
t3_m
Authentic Ack
t4_m
FTM_(m+1) payload contains [t1_m, t4_m’]
t1_(m+1)
t2_(m+1)
Fake Ack
t4_(m+1)’
Authentic Ack
t3_(m+1)
t4_(m+1)
Fig. 1 Illustration of an FTM ranging security issue
Qi Wang, et.al., Broadcom

5. Feasibility of Secure Ranging
The methods proposed in IEEE az 2016/1020 [2] demonstrate the feasibility of improving ranging security in an associated mode.
Qi Wang, et.al., Broadcom

6. Proposed Functional Requirement
We propose to add the following requirement to the az Functional Requirement document [3] under the section of “Range measurement and coverage”
“TGaz Rx: The az protocol shall describe one or more mechanisms to provide secure range measurement in an associated mode.”
Qi Wang, et.al., Broadcom

7. Straw Poll
Do you support to add the following requirement to the az Functional Requirement document [3] under the section of “Range measurement and coverage”
“TGaz Rx: The az protocol shall describe one or more mechanisms to provide secure range measurement in an associated mode.”
Result: Yes: No: Abstain:
Qi Wang, et.al., Broadcom

8. References
[1] IEEE Std REVmc_D8.0, IEEE Standard for Information Technology – Telecommunications and information exchange between systems, local and metropolitan area networks – Specific requirements, Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications
[2] “Security enhancement to FTM”, IEEE /1020
[3] “Proposed az Functional Requirements”, IEEE /424r3
Qi Wang, et.al., Broadcom