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Other AKMs (OWE, TDLS, PASN)

AKM suites outside the PSK, SAE, Enterprise, and FILS categories. These serve specialized roles: opportunistic encryption, direct peer links, pre-association security negotiation, and one deprecated suite.

OWE: AKM 18

Opportunistic Wireless Encryption, marketed as "Enhanced Open."

OWE provides encryption on open networks without requiring a password. The AP and STA perform an unauthenticated Diffie-Hellman key exchange during association, deriving a PMK from the shared secret.

Key Derivation

DH shared secret S = scalar-op(STA_priv, AP_pub)   -- ECDH
s = F(S)                                            -- x-coordinate extraction
prk = HKDF-Extract(STA_pub || AP_pub || group, s)   -- RFC 5869
PMK = HKDF-Expand(prk, "OWE Key Generation", n)     -- n = hash digest length
PMKID = Truncate-128(Hash(STA_pub || AP_pub))

Then the standard 4-way handshake proceeds using this PMK.

Security Properties

  • Protects against passive eavesdropping: each session uses a unique DH key pair, so captured frames are unreadable without the session private key.
  • Does NOT authenticate the AP: a rogue AP can complete the DH exchange and observe traffic. OWE offers no protection against active MITM.
  • No password: there is nothing to crack. The PMK is derived from fresh DH randomness, not from a static secret.

OWE is designed for public hotspots where some confidentiality is better than none, but where certificate-based authentication is impractical.

Spec References

  • OWE: 802.11-2024 §12.14
  • DH group negotiation: §12.14.2
  • RFC 8110 (OWE definition)

TDLS: AKM 7

Tunneled Direct-Link Setup allows two stations associated to the same AP to establish a direct encrypted link for peer-to-peer communication, without routing traffic through the AP.

Key Derivation

TDLS uses a separate handshake (the TDLS Setup Request/Response/Confirm exchange) to establish a Tunnel Peer Key (TPK). The derivation is two steps (§12.7.8.2):

TPK-Key-Input = Hash(min(SNonce, ANonce) || max(SNonce, ANonce))
TPK = KDF-Hash-Length(TPK-Key-Input,
                      "TDLS PMK",
                      min(MAC_I, MAC_R) || max(MAC_I, MAC_R) || BSSID)

Where Hash and KDF-Hash-Length use the hash algorithm negotiated via the AKM suite, MAC_I / MAC_R are the initiator and responder MAC addresses, and BSSID is the AP through which both stations are associated. The nonces and MACs are min/max sorted to ensure both sides compute the same value regardless of initiator role.

The TPK is then split into the TPK-KCK and TPK-TK. This handshake runs inside the existing 802.11 data channel (encapsulated in 802.11 data frames), so it is protected by the AP's PTK.

Usage

TDLS is negotiated between stations using TDLS Action frames. The AP is not involved in the key exchange. Primarily used for high-throughput peer-to-peer scenarios (media streaming, file transfer) to avoid the AP bottleneck.

Spec References

  • TDLS: 802.11-2024 §11.20, §12.7.8, §12.7.8.2

PASN: AKM 21

Pre-Association Security Negotiation, introduced in 802.11az-2022.

PASN enables a station and AP to establish a secure channel before the standard authentication/association procedure. This is required for:

  • Secure 802.11az ranging (Fine Timing Measurement with security)
  • Location services requiring pre-association encryption
  • Bootstrapping credentials before association

Key Derivation

PASN uses a 3-way authentication handshake (PASN Authentication frames 1, 2, 3) to establish a PTKSA. The PMK used as input depends on the base AKM: it comes from an existing PMKSA (SAE, FILS, 802.1X) or is derived via PASN's own mechanism when the base AKM is PASN itself.

PTK = KDF-Hash-NNN(PMK, "PASN PTK Derivation", SPA || BSSID || DHss)

Where DHss is the Diffie-Hellman shared secret from the ephemeral key exchange in the PASN Authentication frames, and Hash/NNN depend on the base AKM (SHA-256 with NNN=640 for PASN AKMP).

Usage

PASN is primarily a protocol primitive, not an end-user configuration option. It is invoked by services that need secure pre-association communication, particularly 802.11az ranging.

Spec References

  • PASN: 802.11-2024 §12.13, §12.13.8 (PTKSA derivation)

APPeerKey: AKM 10 (Deprecated)

AKM 10 was defined for direct AP-to-AP key exchange in mesh or infrastructure contexts. It was deprecated and has been removed from active use in the standard. AKM 10 should not appear in modern deployments.

No attack surface exists because the AKM is not deployed.