Comment 94 for bug 339313

actually there is really no reliable method available. that it works for you is pure luck. depending on the AP manufacturer, another hash is used. So it can very well be that most of the APs sold in you town come from the same manufacturer have the same hash. But for others it won't work.
By the way, windows has the exact same problem. Their solution is to provide a hash anyway, but then it magicaly fails on certain wireless networks and you have no idea why.
Not sure whatthe best thing to do is, i think there will be less problems if there is no hash provided for 64bit wep (which is depreciated anyway).