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When Bad WEP Happens to Good Macs

July 6, 2004

I ran into a weird situation the other day with a Mac laptop (running OS X Panther) that couldn’t get on a local WEP-protected wireless network.  It would appear to see the network fine, with full signal strength, but would never get an address via DHCP, and (of course) you couldn’t go anywhere or do anything.

As I mentioned, the wi-fi network was WEP protected, so it should have asked for a “password” (the WEP key) when the network was selected.  Since it didn’t, the implication is that it was already entered, and added to the keychain.

But what if it was wrong?


Theoretically, you shouldn’t be able to enter a bad WEP key—if you enter the key incorrectly, OS X should re-prompt you for the key.  Even so, you can still end up with a bad WEP key, if the WEP key on the access point is changed.

I’m not sure whether that is what happened in this case, or whether somehow OS X managed to let a bad key get entered, but in any event, the result is the same—OS X will let you select the network, you’ll appear to be connected, but there’s no meaningful communication actually occuring, DHCP won’t operate, and you won’t be prompted for a new password.

It took me awhile to figure out how to actually view and change the WEP password.  I’d assumed that it’d be somewhere in the various network preferences dialogs, but it wasn’t—yes, I’m still an OS X newbie, and I didn’t find much help online (which is why I’m bothering to write this up, in case someone else runs into it.)

Where you need to go is to Keychain Access (Applications : Utility : Keychain Access).  Scroll for an entry named the same as the network name (the SSID).  Click on it, and click on “Show Password” (you’ll be prompted for your admin password).  Edit the password to be the proper WEP key, and click “Save Changes”.  Turn your Airport card off and back on from the Airport dropdown on the menu bar, and you should magically be good to go.

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