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Security Related Modifications to 802.11e-D4.3 Direct Link Protocol

Security Related Modifications to 802.11e-D4.3 Direct Link Protocol. Carlos Rios RiosTek LLC. D4.3 DLP Summary. DLP per 802.11e-D4.3 is a simple protocol to allow non-AP QSTAs to communicate directly while actively maintaining a BSS association

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Security Related Modifications to 802.11e-D4.3 Direct Link Protocol

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  1. Security Related Modifications to 802.11e-D4.3 Direct Link Protocol • Carlos Rios • RiosTek LLC

  2. D4.3 DLP Summary • DLP per 802.11e-D4.3 is a simple protocol to allow non-AP QSTAs to communicate directly while actively maintaining a BSS association • Adds just three new Action Frames to 802.11-1999DLP-Request, relayed through AP, lets QSTA1 ask QSTA2 to dance DLP-Response, relayed through AP, provides QSTA1 with an answerDLP-Probe optionally allows QSTAs to gauge the direct link • The AP serves as a “Gatekeeper and Facilitator” in setting up the DLP • However, this protocol has a serious shortcoming • Essential security elements consistent with ongoing activities in TGi are not incorporated

  3. Proposed DLP Modifications DLP Request/Response AP 1b 1a • QSTA-1 sends DLP-Request to QSTA-2 via AP (1a) • DLP-Request contains STA-1 Capabilities, Supported Rates, RSN Information Element • AP forwards the DLP-Request to QSTA-2 (1b) • If QSTA-2 is in Power Save mode, then AP buffers the frame, and announces pending traffic to QSTA-2 in the TIM, so that QSTA-2 can retrieve it as desired • Else: If BSS policy disallows DLP, AP returns DLP-Response to QSTA-1 with status code “Not Allowed” • Else: If QSTA-2 not in the BSS, then AP returns DLP-Response to STA-1 with status code “Not Present” • QSTA-2, agreeing to DLP, transmits a DLP-Response to AP with Status Code “Success” (2a) • DLP-Response contains QSTA-2 Capabilities, Supported Rates, RSN IE • Else: If QSTA-2 refuses to DLP, returns DLP-Response with status code “Refused” • AP forwards the DLP-Response frame to QSTA-1 (2b) 2b 2a QSTA-1 QSTA-2

  4. DLP Protocol Security Modifications AP DLP-Request/Response 2b 1b 1a DLP-Key 2a • DLP enabled, but QSTAs don’t possess keys to establish a secure RSN/TSN session • The AP, knowing both QSTAs’ RSNIEs, selects highest-security-level common authentication and cipher suites • The AP calculates an appropriate QSTA-1/QSTA-2 DLP Pairwise Master Key • The AP distributes selected authentication and cipher suites and the DLP PMK to QSTA-1 (3a) and QSTA-2 (3b) in (encrypted Authentication frame) DLP-Key messages • The AP then promptly clears its DLP PMK register and “forgets” the key • QSTA-1 and QSTA-2 then immediately execute direct mutual authentication and encryption key derivation/management handshake, and establish a secure DLP link • QSTA-1/QSTA-2 “Link Quality” can be gauged during the authentication handshake, or by using the optional DLP-Probe frames • STAs shall stay awake for a “no-activity” timeout period following every reception. • If either STA times out further data exchange shall be routed through the AP until and if another DLP session is established • Stations maintain a cache with the side channel capabilities on a per destination STA basis (Optional) Probe, Mutual Authentication, Direct Traffic 3a 3b 4 STA-1 STA-2

  5. Why do this? • QSTAs associated with a common AP may nevertheless implement different security protocols (WEP, TKIP, CCMP)- So which should they implement with each other? • The AP can serve as a “security facilitator”, since it already knows the QSTAs’ security capabilities, thereby authorizing the DLP • It automatically determines the strongest security protocol common to both and “suggests” they implement it • As a nice incentive, the AP also generates and distributes appropriate key material so the QSTAs can derive necessary encryption keys • AP uses one encrypted Authentication frame for this purpose, sent independently to both stations • Otherwise the QSTAs need to “authorize” their session by manually exchanging encryption keys outside of 802.11 • The QSTAs, authorized to DLP via either mechanism, above, then begin a mutual authentication exchange • Mutual Authentication successful, QSTAs can immediately thereafter exchange secure traffic

  6. Proposed DLP Modifications Summary • The modified DLP remains a simple protocol, but now allows ready incorporation of TGi security. • DLP-Key Authentication frame, transmitted from the AP to each QSTA, provides the essential security elements • The AP still serves as a “Gatekeeper and Facilitator” in setting up the DLP, but now is also “Security Chief” • The herein modified DLP is a more comprehensive and robust solution • Candidate normative text revisions to 802.11e-D4.3, as it has been or may subsequently be modified per ongoing TGe direction, are contained in 03/050r3

  7. Motion • “Move to instruct the Technical Editor to work with the submitter to incorporate the security related DLP Modifications contained in document 03/50r3 into the successor document to 802.11e-D4.3”

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