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How can I connect to a WLAN with WPA-PSK using a 5 character pre-shared key?

Windows is trying to be too smart and refuses to set a password that is shorter than 8 characters.

But it is a public WLAN that I do not own, so cannot change the password in the router...

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The short answer is, you can't, becuase Windows (and other OS/devices) are trying to follow what was laid out by the IEEE society.

There is a quesiton about this over on ServerFault entitled "Can a WPA key be shorter than 8 characters?".

It seems technically you CAN, and it depends on how the WPA-PSK device's manufacturer interpreted the IEEE 802.11i-2004 document.

As the user who answered the linked question on SF points out, the document makes this 'assumption' when discussing security considerations in the "Suggested pass-phrase-to-PSK mapping" section:

A pass-phrase is a sequence of between 8 and 63 ASCII-encoded characters. The limit of 63 comes from the desire to distinguish between a pass-phrase and a PSK displayed as 64 hexadecimal characters.

So it seems you may be stuck until the WLAN is brought up to met that 'standard' of a min. 8 characters that Windows 7 (and apparently at least also Ubuntu) expects.

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I was thinking of using the netsh wlan command to export the profile, edit the passphrase and import it back. But if it's a limitation in the device drivers and/or the OS, and not the GUI then it will obviously not work... I was also hoping for a secret Registry key that used to be the solution in case of Windows problems for so long.... ;-) –  Gabor Kulcsar Jul 15 '11 at 18:16
    
Secret registry keys. . . Ah ha! You are the reason why Microsoft keeps all that appcompat in their files!! :) –  surfasb Jul 15 '11 at 18:29
    
@Gabor Kulcsar - That's a valid thing to try, as I'm not sure if it's (just) the GUI limiting you to 8 characters, or the Wireless 'stack'. I tried what you suggested with netsh here on a WPA-PSK network. After exporting to XML, changing the "<protected>" key to False, entering the PSK in plain text in the "<keymaterial>" key, and adding it back as a new profile it did connect to our wireless with that profile. But our key is over 8 chars, so it'd be interesting to see if you idea works for you and the 5-digit pass-phrase - try it and let us know. :) –  Ƭᴇcʜιᴇ007 Jul 15 '11 at 18:39
    
Nah, it still says the key is too short and that the profile file is damaged. So I accept your answer and then I'll go and complain in the pub that they should change their password... I doubt they will do that though. –  Gabor Kulcsar Jul 15 '11 at 18:46
    
@Gabor Kulcsar - Crappy, I was kind of hoping it WOULD work for that, in case I ever ran into it. :) –  Ƭᴇcʜιᴇ007 Jul 15 '11 at 20:13

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