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This discussion of WPA3 OWE seems to imply that WiFi at Starbucks/the airport/whatever can be secured against an evil twin attack if they use WPA3-Personal instead of OWE. But it seems like that wouldn't actually do anything.

If I'm at some place with public WiFi, that necessarily means the password is public. So what prevents me from setting up an evil twin using the same password? It seems to me that there's no real difference between OWE and WPA3-Personal if the password is public.

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  • Fixed my previous comment: "if they use PSK instead of OWE", I guess you mean SAE (which is what replaces PSK in WPA3).
    – ysdx
    May 2 at 6:32
  • @ysdx Saying SAE or WPA3-Personal is probably more correct, but isn't it true that "PSK" is accurate as a descriptive term, given that WPA3-Personal uses a pre-shared key? May 2 at 18:19
  • 1
    I updated the title and question to use "password" and "WPA3-Personal" instead of "PSK" May 2 at 18:21

2 Answers 2

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PSK-based authentication -- called Simultaneous Authentication of Equals (SAE) in WPA3 -- cannot prevent evil-twin attacks if the PSK is publicly known. As the name already suggests, the protocol does not even distinguish between a wi-fi user and an access point. Anybody who knows the PSK can complete the authentication procedure -- and pretend to be the AP. The goal of SAE is to protect PSKs which are not publicly shared.

If you want AP authentication, you need to use EAP-TLS (i.e., WPA3-Enterprise) and validate the AP certificate.

edit: As ysdx points out, this is only true for plain SAE without the SAE-PK extension.

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In theory, you can have a protection against evil twin attack when using WPA3 Personal (SAE) using the SAE-PK extension. It works by associating a public key to the Access Point.

This public key can be provisioned to the stations with the K: component of the Wifi QR code, which contains the SubjectPublicKeyInfo encoded in base64.

7.1 URI format

The URI is defined by [7] and formatted by the WIFI-qr ABNF rule:

WIFI-qr = “WIFI:” [type “;”] [trdisable “;”] ssid “;”
                  [hidden “;”] [id “;”] [password “;”]
                  [publickey “;”] “;”

[... (other keywords) ...]

public-key = “K:” *PKCHAR
  ;; DER of ASN.1 `SubjectPublicKeyInfo` in compressed form and
  ;;  encoded in “base64” as per [6], present when the network
  ;;  supports SAE-PK, else absent

I have yet to see support for any of this however.

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  • 3
    Excellent answer. To protect new users, you do need to make sure that the QR code can't just be covered up with a sticker from the attacker, though. Apr 25 at 13:24
  • @Michaelcomelately, yes indeed :)
    – ysdx
    Apr 25 at 16:26

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